Specification: Jakarta Standard Tag Library

Version: 3.0

Status: FINAL

Release: April 11, 2022

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Preface

This is the Jakarta Standard Tag Library 3.0 specification, developed by the Jakarta Standard Tag Library Team, https://projects.eclipse.org/projects/ee4j.jstl

Oracle, Java, and MySQL are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners.

Implementors of Jakarta Standard Tag Lbrary and authors of Jakarta Server Pages may find the following documents worth consulting for additional information:.

Jakarta Server Pages

Jakarta Server Pages Project
Jakarta Server Pages Specification

Jakarta Servlet

Jakarta Servlet Project
Jakarta Servlet Specification

Java™, Standard Edition, Version 8.0 API Specification

https://docs.oracle.com/javase/8/docs/api

Jakarta EE

https://jakarta.ee

JavaBeans

https://docs.oracle.com/javase/8/docs/technotes/guides/beans

JDBC

https://docs.oracle.com/javase/8/docs/technotes/guides/jdbc

Java Technology and XML

https://docs.oracle.com/javase/8/docs/technotes/guides/xml

XPath specification

http://www.w3.org/TR/xpath

XML home page at W3C

http://www.w3.org/XML

HTML home page at W3C

http://www.w3.org/MarkUp

XML.org home page

http://www.xml.org

Typographical Conventions

Font Style Uses

Italic

Emphasis, definition of term.

Monospace

Syntax, code examples, attribute names, Java language types, API, enumerated attribute values.

Acknowledgments

The Jakarta Standard Tag Library specification is the result of collaborative work involving many individuals, all driven by a common goal of designing the best libraries possible for the Jakarta Server Pages author community.

The current members of the Jakarta Standard Tag Library project in the Eclipse Foundation can be found at the following location: https://projects.eclipse.org/projects/ee4j.jstl/who.

We would like to thank all members of the JSR-52 expert group under the Java Community Process: Nathan Abramson, Shawn Bayern, Hans Bergsten, Paul Bonfanti, Vince Bonfanti, David Brown, Larry Cable, Tim Dawson, Morgan Delagrange, Bob Foster, David Geary, Scott Hasse, Hal Hildebrand, Jason Hunter, Serge Knystautas, Mark Kolb, Wellington Lacerda, Jan Luehe, Geir Magnusson Jr., Dan Malks, Craig McClanahan, Richard Morgan, Glenn Nielsen, Rickard Oberg, Joseph B. Ottinger, Eduardo Pelegri-Llopart, Sam Pullara, Tom Reilly, Brian Robinson, Russ Ryan, Pasi Salminen, Steven Sargent, Allan Scott, Virgil Sealy, Magnus Stenman, Gael Stevens, James Strachan, Christine Tomlinson, Norbert von Truchsess, Keyton Weissinger, Clement Wong, Alex Yiu.

This specification was first initiated by Eduardo Pelegri-Llopart. Eduardo’s leadership in making the Java platform the best technology available for the web layer has been key in shaping the vision behind the standard tag library.

Shawn Bayern and Hans Bergsten deserve special credit for being actively involved in all design issues of this specification. Their vast expertise and commitment to excellence has had a profound impact in every single aspect of this specification. Mille mercis Shawn et Hans! Don’t know how we would have done it without you two.

Many thanks to Jan Luehe for taking ownership of the internationalization and formatting chapters of this specification on short notice, and doing an incredible job.

Special mention to Nathan Abramson for being a driving force behind the expression language introduced in JSTL, to James Strachan for leading the group in our understanding of XML for page authors, and to Craig McClanahan for his help on servlet and J2EE platform related issues.

This specification has drawn a lot of its design ideas from pioneers in the field of tag libraries. We are grateful to the Jakarta project at Apache, as well as other efforts in the industry, where projects led by Craig McClanahan (Struts), James Strachan (XTags), Morgan Delagrange (DBTags), Tim Dawson (I18N), Glenn Nielsen (many utility taglibs), Scott Hasse (JPath), Dmitri Plotnikov (JXPath), Pasi Salminen (O&D Struts), have greatly influenced the design of the JSTL libraries.

The RI team composed of Shawn Bayern (lead), Nathan Abramson, Justyna Horwat, and Jan Luehe has done a wonderful job at turning code faster than the specification could be written.

Quality has been in the capable hands of Ryan Lubke, lead of the TCK team under the Java Community Process that also includes Lance Andersen. David Geary’s help in doing thorough reviews of the specification was also greatly appreciated.

We are also grateful to the product team at Sun Microsystems who helped us sail efficiently through this specification: Jim Driscoll, Karen Schaffer, George Grigoryev, Stephanie Bodoff, Vanitha Venkatraman, Prasad Subramanian, and Xiaotan He.

Finally, we’d like to thank the community at large for their ever increasing interest in this technology. We sure hope you’ll enjoy the Jakarta Standard Tag Library.

Comments

We are interested in improving this specification and welcome your comments and suggestions. You can email your comments to us at:

jstl-dev@eclipse.org

1. Introduction

The Jakarta Standard Tag Library provides a specification document, API and TCK that extends the Jakarta Server Pages specification by adding a tag library of Jakarta Server Pages tags for common tasks, such as XML data processing, conditional execution, database access, loops and internationalization.

1.1. Goals

The ultimate goal of the Jakarta Standard Tag Library is to help simplify Jakarta Server Pages authors' lives.

A page author is someone who is responsible for the design of a web application’s presentation layer using Jakarta Server Pages. Many page authors are not fluent in any programming language.

One of the main difficulties a page author is faced with is the need to use a scripting language (the default being the Java programming language) to manipulate the dynamic data within a Jakarta Server Pages page. Unfortunately, page authors often see scripting languages as complex and not very well adapted to their needs.

The Jakarta Standard Tag Library offers the following capabilities:

  • General-purpose actions
    These actions complement the expression language by allowing a page author to easily display expressions in the expression language, set and remove the value of Jakarta Server Pages scoped attributes, as well as catch exceptions.

  • Control flow actions
    Tag-based control flow structures (conditionals, iterators), which are more natural to page authors.

  • Tag library validators (TLVs)
    TLVs allow projects to only allow specific tag libraries, as well as enforce Jakarta Server Pages coding styles that are free of scripting elements.

The other key aspect of the Jakarta Standard Tag Library is that it provides standard actions and standard Expression Language functions for functionality most often needed by page authors. These cover the following topics:

  • Accessing URL-based resources

  • Internationalization (i18n) and text formatting

  • Relational database access (SQL)

  • XML processing

  • String manipulation

1.2. Multiple Tag Libraries

A tag library is a collection of actions that encapsulates functionality to be used from within a Jakarta Server Pages page. The Jakarta Standard Tag Library includes a wide variety of actions that naturally fit into discrete functional areas. This is why the Jakarta Standard Tag Library, although referred to as the standard tag library (singular), is exposed via multiple tag libraries to clearly identify the functional areas it covers, as well as to give each area its own namespace. The tables below lists these functional areas along with the URIs used to reference the libraries. The tables also show the prefixes used in this specification (although page authors are free to use any prefix they want).

Jakarta Standard Tag Library Tag Libraries

Functional Area URI Prefix

core

jakarta.tags.core

c

XML processing

jakarta.tags.xml

x

I18N capable formatting

jakarta.tags.fmt

fmt

relational db access (SQL)

jakarta.tags.sql

sql

Functions

jakarta.tags.functions

fn

1.3. Container Requirement

Jakarta Standard Tag Library requires a Jakarta Server Pages 3.0 web container. Please note that the expression language is an individual specification: Jakarta Expression Language 4.0.

2. Conventions

This chapter describes the conventions used in this specification.

2.1. How Actions are Documented

The Jakarta Standard Tag Library actions are grouped according to their functionality. These functional groups of actions are documented in their own chapter using the following structure:

  • Motivation
    Describes the motivation for standardizing the actions.

  • Overview
    Provides an overview of the capabilities provided by the actions. Sample code featuring these actions in their most common use cases is also provided.

  • One section per action, with the following structure:

    • Name
      Tag library prefixes are used in this specification for all references to Jakarta Standard Tag Library actions (e.g.: <c:if> instead of <if>).

    • Short Description

    • Syntax
      The syntax notation is described in Syntax Notation.

    • Body Content
      This section specifies which type of body content is supported by the action. As defined by the Jakarta Server Pages specification, the body content type can be one of empty, JSP, or tagdependent. The section also specifies if the body content is processed by the action or is simply ignored by the action and just written to the current JspWriter. If the body content is processed, information is given on whether or not the body content is trimmed before the action begins processing it.

    • Attributes
      Details in Attributes below.

    • Constraints
      List of additional constraints enforced by the action.

    • Null & Error Handling
      Details on how null and empty values are processed, as well as on exceptions thrown by the action.

    • Description
      This section provides more details on the action.

    • Other sections
      Other sections related to the group of actions described in the chapter may exist. These include sections on interfaces and classes exposed by these actions.

2.1.1. Attributes

For each attribute, the following information is given: name, dynamic behavior, type, and description.

The rtexprvalue element defined in a TLD is covered in this specification with the column titled "Dynamic" that captures the dynamic behavior of an attribute. The value can be either true or false. A false value in the dynamic column means that only a static string value can be specified for the attribute. A true value means that a request-time attribute value can be specified. As defined in the Jakarta Server Pages specification, a "request-time attribute value" can be either a Java expression, an Expression Language expression, or a value set by a <jsp:attribute>.

2.1.2. Syntax Notation

[…​]

What is inside the square brackets is optional

{option1|option2|option3|…​}

Only one of the given options can be selected

value

The default value

For example, in the syntax below:

<c:set var="varName" [scope="{page|request|session|application}"] value="value"/>

the attribute scope is optional. If it is specified, its value must be one of page, request, session, or application. The default value is page.

2.2. Scoped Variables

Actions usually collaborate with their environment in implicit or explicit ways, or both.

Implicit collaboration is often done via a well defined interface that allows nested tags to work seamlessly with the ancestor tag exposing that interface. The Jakarta Standard Tag Library iterator tags support this mode of collaboration.

Explicit collaboration happens when a tag explicitly exposes information to its environment. Traditionally, this has been done by exposing a scripting variable with a value assigned from a Jakarta Server Pages scoped attribute (which was saved by the tag handler). Because of the expression language, the need for scripting variables is significantly reduced. This is why all the Jakarta Standard Tag Library tags expose information only as Jakarta Server Pages scoped attributes (no scripting variable exposed). These exported Jakarta Server Pages scoped attributes are referred to as scoped variables in this specification; this helps in preventing too much overloading of the term "attribute".

2.2.1. var and scope

The convention is to use the name var for attributes that export information. For example, the <c:forEach> action exposes the current item of the customer collection it is iterating over in the following way:

<c:forEach var="customer" items="${customers}">
    Current customer is <c:out value="${customer}"/>
</c:forEach>

It is important to note that a name different than id was selected to stress the fact that only a scoped variable (Jakarta Server Pages scoped attribute) is exposed, without any scripting variable.

If the scoped variable has at-end visibility (see Visibility), the convention also establishes the attribute scope to set the scope of the scoped variable.

The scope attribute has the semantics defined in the Jakarta Server Pages specification, and takes the same values as the ones allowed in the <jsp:useBean> action; i.e. page, request, session, application. If no value is specified for scope, page scope is the default unless otherwise specified.

It is also important to note, as per the Jakarta Server Pages specification, that specifying "session" scope is only allowed if the page has sessions enabled.

If an action exposes more than one scoped variable, the main one uses attribute names var and scope, while secondary ones have a suffix added for unique identification. For example, in the <c:forEach> action, the var attribute exposes the current item of the iteration (main variable exposed by the action), while the varStatus attribute exposes the current status of the iteration (secondary variable).

2.2.2. Visibility

Scoped variables exported by Jakarta Standard Tag Library actions are categorized as either nested or at-end.

Nested scoped variables are only visible within the body of the action and are stored in "page" scope[1]. The action must create the variable according to the semantics of PageContext.setAttribute(varName,PAGE_SCOPE), and it must remove it at the end of the action according to the semantics of PageContext.removeAttribute(varName, PAGE_SCOPE) .[2]

At-end scoped variables are only visible at the end of the action. Their lifecycle is the one associated with their associated scope.

In this specification, scoped variables exposed by actions are considered at-end by default. If a scoped variable is nested, it will be explicitly stated.

2.3. Static vs Dynamic Attribute Values

Except for the two exceptions described below, attribute values of Jakarta Standard Tag Library actions can always be specified dynamically (see Attributes).

The first exception to this convention is for the select attribute of XML actions. This attribute is reserved in the Jakarta Standard Tag Library to specify a String literal that represents an expression in the XPath language.

The second exception is for attributes that define the name and scope of scoped variables (as introduced in Attributes) exported by Jakarta Standard Tag Library actions.

Restricting these attributes to static values should benefit development tools, without any impediment to page authors.

2.4. White Spaces

Following the Jakarta Server Pages specification (as well as the XML and XSLT specifications), whitespace characters are #x20, #x9, #xD, or #xA.

2.5. Body Content

If an action accepts a body content, an empty body is always valid, unless explicitly stated otherwise.

If the body content is used to set the value of an attribute, then an empty body content sets the attribute value to an empty string.

If a body content is trimmed prior to being processed by the action, it is trimmed as defined in method trim() of the class java.lang.String.

2.6. Naming

The Jakarta Standard Tag Library adopts capitalization conventions of Java variables for compound words in action and attribute names. Recommended tag prefixes are kept lowercase. Thus, we have <sql:transaction> and <c:forEach>, as well as attributes such as docSystemId and varDom.

In some cases, attribute names for Jakarta Standard Tag Library actions carry conventional meanings. For instance, var and scope discussed the var and scope attibutes. The select Attribute discusses the select attribute used in Jakarta Standard Tag Library’s XML-processing tag library.

2.7. Errors and Exceptions

All syntax errors (as defined in the syntax section of each action, as well as the syntax of Expression Language expressions) must be reported at translation time.

Constraints, as defined in the constraints section of each action, must also be reported at translation time unless they operate on a dynamic attribute value, in which case errors are reported at runtime.

The conversion from a String value to the expected type of an attribute is handled according to the rules defined in the Jakarta Server Pages specification.

Since it is hard for a page author to deal with exceptions, the Jakarta Standard Tag Library tries to avoid as many exception cases as possible, without causing other problems.

For instance, if <c:forEach> were to throw an exception when given a null value for the attribute items, it would be impossible to easily loop over a possibly missing string array that represents check-box selection in an HTML form (retrieved with an Expression Language expression like ${paramValues.selections}). A better choice is to do nothing in this case.

The conventions used in the Jakarta Standard Tag Library with respect to errors and exceptions are as follows:

  • scope

    • Invalid value – translation time validation error

  • var

    • Empty – translation time validation error

  • Dynamic attributes with a fixed set of valid String values:

    • null – use the default value
      A null value can therefore be used to dynamically (e.g. by request parameter), turn on or off special features without too much work.

    • Invalid value – throw an exception
      If a value is provided but is not valid, it’s likely a typo or another mistake.

  • Dynamic attributes without a fixed set of valid values:
    The rules below assume that if the type of the value does not match the expected type, the Expression Language will have applied coercion rules to try to accomodate the input value. Moreover, if the expected type is one of the types handled by the Expression Language coercion rules, the Expression Language will in most cases coerce null to an approriate value. For instance, if the expected type is a Number, the Expression Language will coerce a null value to 0, if it’s Boolean it will be coerced to false.

    • null – behavior specific to the action
      If this rule is applied, it’s because the Expression Language could not coerce the null into an appropriate default value. It is therefore up to the action to deal with the null value and is documented in the "Null & Error Handling" section of the action.

    • Invalid type – throw an exception

    • Invalid value – throw an exception

  • Exceptions caused by the body content:
    Always propagate, possibly after handling them (e.g. <sql:transaction>).

  • Exceptions caused by the action itself:
    Always propagate, possibly after handling them.

  • Exceptions caused by the Expression Language:
    Always propagate.

  • Exceptions caused by XPath:
    Always propagate.

Page authors may catch an exception using <c:catch>, which exposes the exception through its var attribute. var is removed if no exception has occurred.

When this specification requires an action to throw an exception, this exception must be an instance of jakarta.servlet.jsp.JspException or a subclass. If an action catches any exceptions that occur in its body, its tag handler must provide the caught exception as the root cause of the JspException it re-throws.

Also, by default, Jakarta Standard Tag Library actions do not catch or otherwise handle exceptions that occur during evaluation of their body content. If they do, it is documented in their "Null & Error Handling" or "Description" section.

2.8. Configuration Data

Context initialization parameters (see Servlet specification) are useful to configure the behavior of actions. For example, it is possible in the Jakarta Standard Tag Library to define the resource bundle used by I18N actions via the deployment descriptor (web.xml) as follows:

<web-app>
...
    <context-param>
        <param-name>jakarta.servlet.jsp.jstl.fmt.localizationContext</param-name>
        <param-value>com.acme.MyResources</param-value>
    </context-param>
...
</web-app>

In many cases, it is also useful to allow configuration data to be overridden dynamically for a particular Jakarta Server Pages scope (page, request, session, application) via a scoped variable. The Jakarta Standard Tag Library refers to scoped variables used for that purpose as configuration variables.

According to the Jakarta Server Pages specification (Jakarta Server Pages.2.8.2), a scoped variable name should refer to a unique object at all points in the execution. This means that all the different scopes (page, request, session, and application) that exist within a PageContext really should behave as a single name space; setting a scoped variable in any one scope overrides it in any of the other scopes.

Given this constraint imposed by the Jakarta Server Pages specification, and in order to allow a configuration variable to be set for a particular scope without affecting its settings in any of the other scopes, the Jakarta Standard Tag Library provides the jakarta.servlet.jsp.jstl.core.Config class. The Config class transparently manipulates the name of configuration variables so they behave as if scopes had their own private name space. Details on the name manipulations involved are voluntarily left unspecified and are handled transparently by the Config class. This ensures flexibility should the "scope name space" issue be addressed in the future by the Jakarta Server Pages specification.

When setting configuration data via the deployment descriptor, the name associated with the context initialization parameter (e.g. jakarta.servlet.jsp.jstl.fmt.localizationContext) must be used and only String values may be specified. Configuration data that can be set both through a context initialization parameter and configuration variables is referred to as a configuration setting in this specification.

As mentioned above, application developers may access configuration data through class jakarta.servlet.jsp.jstl.core.Config. As a convenience, constant String values have been defined in the Config class for each configuration setting supported by the Jakarta Standard Tag Library. The values of these constants are the names of the context intialization parameters.

Each configuration variable clearly specifies the Java data type(s) it supports. If the type of the object used as the value of a configuration variable does not match one of those supported by the configuration variable, conversion is performed according to the conversion rules defined in the expression language. Setting a configuration variable is therefore exactly the same as setting an attribute value of an action using the Expression Language. A failure of these conversion rules to determine an appropriate type coersion leads to a JspException at runtime.

2.9. Default Values

It is often desirable to display a default value if the output of an action yields a null value. This can be done in a generic way in the Jakarta Standard Tag Library by exporting the output of an action via attribute var, and then displaying the value of that scoped variable with action <c:out>.

For example:

<fmt:formatDate var="formattedDate" value="${reservationDate}"/>
Date: <c:out value="${formattedDate}" default="not specified"/>

3. Expression Language Overview

Jakarta Standard Tag Library makes use of the Jakarta Expression Language.

This chapter provides a simple overview of the key features of the expression language, it is therefore non-normative. Please refer to the Jakarta Expression Language specification for the formal definition of the Expression Language.

3.1. Expressions and Attribute Values

The Expression Language is invoked exclusively via the construct ${expr}. In the sample code below, an Expression Language expression is used to set the value of attribute test, while a second one is used to display the title of a book.

<c:if test="${book.price <= user.preferences.spendingLimit}">
    The book ${book.title} fits your budget!
</c:if>

It is also possible for an attribute to contain more than one Expression Language expression, mixed with static text. For example, the following would display "Price of productName is productPrice" for a list of products.

<c:forEach var="product" items="${products}">
    <c:out value="Price of ${product.name} is ${product.price}"/>
</c:forEach>

3.2. Accessing Application Data

An identifier in the Expression Language refers to the Jakarta Server Pages scoped variable returned by a call to PageContext.findAttribute(identifier). This variable can therefore reside in any of the four Jakarta Server Pages scopes: page, request, session, or application. A null value is returned if the variable does not exist in any of the scopes.

The Expression Language also defines implicit objects to support easy access to application data that is of interest to a page author. Implicit objects pageScope, requestScope, session Scope, and applicationScope provide access to the scoped variables in each one of these Jakarta Server Pages scopes. It is also possible to access HTTP request parameters via the implicit objects param and paramValues. The implicit object param is a Map object where param["foo"] returns the first string value associated with request parameter foo, while paramValues["foo"] returns an array of all string values associated with that request parameter.

The code below displays all request parameters along with all their associated values.

<c:forEach var="aParam"items="${paramValues}">
    param: ${aParam.key}
    values:
    <c:forEach var="aValue" items="${aParam.value}">
        ${aValue}
    </c:forEach>
    <br>
</c:forEach>

Request headers are also accessible in a similar fashion via implicit objects header and headerValues. initParam gives access to context initialization parameters, while cookie exposes cookies received in the request.

Implicit object pageContext is also provided for advanced usage, giving access to all properties associated with the PageContext of a Jakarta Server Pages page such as the HttpServletRequest, ServletContext, and HttpSession objects and their properties.

3.3. Nested Properties and Accessing Collections

The application data that a page author manipulates in a Jakarta Server Pages page usually consists of objects that comply with the JavaBeans specification, or that represent collections such as lists, maps, or arrays.

The Expression Language recognizes the importance of these data structures and provides two operators, "." and "[]", to make it easy to access the data encapsulated in these objects.

The "." operator can be used as a convenient shorthand for property access when the property name follows the conventions of Java identifiers. For example:

Dear ${user.firstName}
from ${user.address.city},
thanks for visiting our website!

The "[]" operator allows for more generalized access, as shown below:

<%-- "productDir" is a Map object containing the description of
products, "preferences" is a Map object containing the preferences of a user --%>
product:
${productDir[product.custId]}
shipping preference:
${user.preferences["shipping"]}

3.4. Operators

The operators supported in the Expression Language handle the most common data manipulations. The standard relational, arithmetic, and logical operators are provided in the Expression Language. A very useful "empty" operator is also provided.

The six standard relational operators are supported: == (or eq), != (or ne), < (or lt), > (or gt), (or le), >= (or ge). The second versions of the last 4 operators are made available to avoid having to use entity references in XML syntax.

Arithmetic operators consist of addition (+), subtraction (-), multiplication (*), division (/ or div), and remainder/modulo (% or mod).

Logical operators consist of && (or and), || (or or), and ! (or not).

The empty operator is a prefix operator that can used to determine if a value is null or empty. For example:

<c:if test="${empty param.name}">
    Please specify your name.
</c:if>

3.5. Automatic Type Conversion

The application data a page author has access to may not always exactly match the type expected by the attribute of an action or the type expected for an Expression Language operator. The Expression Language supports an exhaustive set of rules to coerce the type of the resulting value to the expected type.

For example, if request attributes beginValue and endValue are Integer objects, they will automatically be coerced to ints when used with the <c:forEach> action.

<c:forEach begin="${requestScope.beginValue}"
           end="${requestScope.endValue}">
    ...
</c:forEach>

In the example below, the parameter String value param.start is coerced to a number and is then added to 10 to yield an int value for attribute begin.

<c:forEach items="${products}" begin="${param.start + 10}">
    ...
</c:forEach>

3.6. Default Values

Jakarta Server Pages are mostly used in presentation. Experience suggests that it is important to be able to provide as good a presentation as possible, even when simple errors occur in the page. To satisfy this requirement, the Expression Language provides default values rather than errors when failure to evaluate an expression is deemed "recoverable". Default values are type-correct values that allow a page to easily recover from these error conditions.

In the following example, the expression "${user.address.city}" evaluates to null rather than throwing a NullPointerException if there is no address associated with the user object. This way, a sensible default value can be displayed without having to worry about exceptions being thrown by the Jakarta Server Pages page.

City: <c:out value="${user.address.city}" default="N/A"/>

In the following example, the addition operator considers the value of param.start to be 0 if it is not defined, therefore evaluating the expression to 10.

<c:forEach items="${products}" begin="${param.start + 10}">
    ...
</c:forEach>

4. General-Purpose Actions: core tag library

This chapter introduces general purpose actions to support the manipulation of scoped variables as well as to handle error conditions.

4.1. Overview

The <c:out> action provides a capability similar to Jakarta Server Pages expressions such as <%= scripting-language-expression %> or ${el-expression}. For example:

You have <c:out value="${sessionScope.user.itemCount}"/> items.

By default, <c:out> converts the characters <, >, ', ", & to their corresponding character entity codes (e.g. < is converted to <). If these characters are not converted, the page may not be rendered properly by the browser, and it could also open the door for cross-site scripting attacks (e.g. someone could post JavaScript code for closing the window to an online discussion forum). The conversion may be bypassed by specifying false to the escapeXml attribute.

The <c:out> action also supports the notion of default values for cases where the value of an Expression Language expression is null. In the example below, the value "unknown" will be displayed if the property city is not accessible.

<c:out value="${customer.address.city}" default="unknown"/>

The action <c:set> is used to set the value of a Jakarta Server Pages scoped attribute as follows:

<c:set var="foo" value="value"/>

It is also possible to set the value of a scoped variable (Jakarta Server Pages scoped attribute) from the body of the <c:set> action. This solves the problem associated with not being able to set an attribute value from another action. In the past, a tag developer would often implement extra "attributes as tags" so the value of these attributes could be set from other actions.

For example, the action <acme:att1> was created only to support setting the value of att1 of the parent tag <acme:atag> from other actions .

<acme:atag>

 <acme:att1>

 <acme:foo>mumbojumbo</acme:foo>

 </acme:att1>

</acme:atag>

With the <c:set> tag, this can be handled without requiring the extra <acme:att1> tag.

<c:set var="att1">

 <acme:foo>mumbojumbo</acme:foo>

</c:set>

<acme:atag att1="${att1}"/>

In the preceding example, the <c:set> action sets the value of the att1 scoped variable to the output of the <acme:foo> action. <c:set> – like all Jakarta Standard Tag Library actions that create scoped attributes – creates scoped attributes in "page" scope by default.

<c:set> may also be used to set the property of a JavaBeans object, or add or set a specific element in a java.util.Map object. For example:.

<!-- set property in JavaBeans object -->
<c:set target="${cust.address}" property="city" value="${city}"/>

<!-- set/add element in Map object -->
<c:set target="${preferences}" property="color" value="${param.color}"/>

Finally, <c:set> may also be used to set a deferred-value that can later be evaluated by a tag handler. In this case, no scope can be specified. For example:

<!-- set deferred value -->
<c:set var="d" value="#{handler.everythingDisabled}"/>
...

<h:inputText id="i1" disabled="#\{d}"/>
<h:inputText id="i2" disabled="#\{d}"/>

Action <c:remove> is the natural companion to <c:set>, allowing the explicit removal of scoped variables. For example:

<c:remove var="cachedResult" scope="application"/>

Finally, the <c:catch> action provides a complement to the Jakarta Server Pages error page mechanism. It is meant to allow page authors to recover gracefully from error conditions that they can control. For example:

<c:catch var="exception">
<!-- Execution we can recover from if exception occurs -->
...
</c:catch>
<c:if test="${exception != null}">
Sorry. Processing could not be performed because...
</c:if>

4.2. <c:out>

Evaluates an expression and outputs the result of the evaluation to the current JspWriter object.

Syntax

Without a body

<c:out value="value" [escapeXml="{true|false}"]
    [default="defaultValue"] />

With a body

<c:out value="value" [escapeXml="{true|false}"]>
    default value
</c:out>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

value

true

Object

Expression to be evaluated.

escapeXml

true

boolean

Determines whether characters <,>,&,'," in the resulting string should be converted to their corresponding character entity codes. Default value is true.

default

true

Object

Default value if the resulting value is null.

Null & Error Handling

If value is null, the default value takes over. If no default value is specified, it itself defaults to an empty string.

Description

The expression to be evaluated is specified via the value attribute.

If the result of the evaluation is not a java.io.Reader object, then it is coerced to a String and is subsequently emitted into the current JspWriter object.

If the result of the evaluation is a java.io.Reader object, data is first read from the Reader object and then written into the current JspWriter object. This special processing associated with Reader objects should help improve performance when large amount of data must be read and then displayed to the page.

If escapeXml is true, the following character conversions are applied:

Character Character Entity Code

<

&lt;

>

&gt;

&

&amp;

'

&#039;

"

&#034;

The default value can be specified either via the default attribute (using the syntax without a body), or within the body of the tag (using the syntax with a body). It defaults to an empty string.

4.3. <c:set>

Sets the value of a scoped variable or a property of a target object.

Syntax

Syntax 1: Set the value of a scoped variable using attribute value

<c:set value="value"
    var="varName" [scope="{page|request|session|application}"]/>

Syntax 2: Set the value of a scoped variable using body content

<c:set var="varName" [scope="{page|request|session|application}"]>
    body content
</c:set>

Syntax 3: Set a property of a target object using attribute value

<c:set value="value"
    target="target" property="propertyName"/>

Syntax 4: Set a property of a target object using body content

<c:set target="target" property="propertyName">
    body content
</c:set>

Syntax 5: Set a deferred value

<c:set var="varName" value="deferred-value"/>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

value

true

Object

Expression to be evaluated.

var

false

String

Name of the exported scoped variable to hold the value specified in the action. The type of the scoped variable is whatever type the value expression evaluates to.

scope

false

String

Scope for var.

target

true

Object

Target object whose property will be set. Must evaluate to a JavaBeans object with setter property property, or to a java.util.Map object.

property

true

String

Name of the property to be set in the target object.

Null & Error Handling
  • Syntax 3 and 4: Throw an exception under any of the following conditions:

    • target evaluates to null

    • target is not a java.util.Map object and is not a JavaBeans object that supports setting property property.

  • If value is null

    • Syntax 1: the scoped variable defined by var and scope is removed.

      • If attribute scope is specified, the scoped variable is removed according to the semantics of PageContext.removeAttribute(varName, scope).

      • Otherwise, there is no way to differentiate between syntax 1 and syntax 5. The scoped variable is removed according to the semantics of PageContext.removeAttribute(varName), and the variable is removed from the VariableMapper as well.

    • Syntax 3:

      • if target is a Map, remove the entry with the key identified by property.

      • if target is a JavaBean component, set the property to null.

    • Syntax 5:

      • There is no way to differentiate between syntax 1 (where scope is not specified) and syntax 5. The scoped variable is removed according to the semantics of PageContext.removeAttribute(varName), and the variable is removed from the VariableMapper as well.

Description

Syntax 1 and 2 set the value of a the scoped variable identified by var and scope.

Syntax 3 and 4:

  • If the target expression evaluates to a java.util.Map object, set the value of the element associated with the key identified by property. If the element does not exist, add it to the Map object.

  • Otherwise, set the value of the property property of the JavaBeans object target. If the type of the value to be set does not match the type of the bean property, conversion is performed according to the conversion rules defined in the expression language (see Section 1.23. Type Conversion of the Jakarta Expression Language specification). With the exception of a null value, setting a bean property with <c:set> is therefore exactly the same as setting an attribute value of an action using the Expression Language. A failure of these conversion rules to determine an appropriate type coersion leads to a JspException at runtime.

Syntax 5:

  • Map the deferred-value specified to the "var" attribute into the Expression Language VariableMapper.

  • Some implementation notes illustrating how the <c:set> tag handler may process a deferred-value specified for the "value" attribute.

doStartTag()
…​
// 'value' is a deferred-value
// Get the current Expression Language VariableMapper
VariableMapper vm = jspContext.getELContext().getVariableMapper();
// Assign the expression to the variable specified
// in the 'var' attribute, so any reference to that
// variable will be replaced by the expression is
// subsequent Expression Language evaluations.
vm.setVariable(getVar(), (ValueExpression)getValue());
…​

4.4. <c:remove>

Removes a scoped variable.

Syntax
<c:remove var="varName"
          [scope="{page|request|session|application}"]/>
Attributes
Name Dynamic Type Description

var

false

String

Name of the scoped variable to be removed.

scope

false

String

Scope for var.

Description

The <c:remove> action removes a scoped variable.

If attribute scope is not specified, the scoped variable is removed according to the semantics of PageContext.removeAttribute(varName). If attribute scope is specified, the scoped variable is removed according to the semantics of PageContext.removeAttribute(varName, scope).

4.5. <c:catch>

Catches a java.lang.Throwable thrown by any of its nested actions.

Syntax
<c:catch [var="varName"]>
    nested actions
</c:catch>
Body Content

Jakarta Server Pages content. The body content is processed by the Jakarta Server Pages container and the result is written to the current JspWriter.

Attributes
Name Dynamic Type Description

var

false

String

Name of the exported scoped variable for the exception thrown from a nested action. The type of the scoped variable is the type of the exception thrown.

Description

The <c:catch> action allows page authors to handle errors from any action in a uniform fashion, and allows for error handling for multiple actions at once.

<c:catch> provides page authors with granular error handling: Actions that are of central importance to a page should not be encapsulated in a <c:catch>, so their exceptions will propagate to an error page, whereas actions with secondary importance to the page should be wrapped in a <c:catch>, so they never cause the error page mechanism to be invoked.

The exception thrown is stored in the scoped variable identified by var, which always has page scope. If no exception occurred, the scoped variable identified by var is removed if it existed.

If var is missing, the exception is simply caught and not saved.

5. Conditional Actions: core tag library

The output of a Jakarta Server Pages page is often conditional on the value of dynamic application data. A simple scriptlet with an if statement can be used in such situations, but this forces a page author to use a scripting language whose syntax may be troublesome (e.g. one may forget the curly braces).

The Jakarta Standard Tag Library conditional actions make it easy to do conditional processing in a Jakarta Server Pages page.

5.1. Overview

The Jakarta Standard Tag Library conditional actions are designed to support the two most common usage patterns associated with conditional processing: simple conditional execution and mutually exclusive conditional execution.

A simple conditional execution action evaluates its body content only if the test condition associated with it is true. In the following example, a special greeting is displayed only if this is a user’s first visit to the site:

<c:if test="${user.visitCount == 1}">
    This is your first visit. Welcome to the site!
</c:if>

With mutually exclusive conditional execution, only one among a number of possible alternative actions gets its body content evaluated.

For example, the following sample code shows how the text rendered depends on a user’s membership category.

<c:choose>
    <c:when test="${user.category == 'trial'}">
        ...
    </c:when>
    <c:when test="${user.category == 'member'}">
        ...
    </c:when>
    <c:when test="${user.category == 'vip'}">
        ...
    </c:when>
    <c:otherwise>
        ...
    </c:otherwise>
</c:choose>

An if/then/else statement can be easily achieved as follows:

<c:choose>
    <c:when test="${count == 0}">
        No records matched your selection.
    </c:when>
    <c:otherwise>
        ${count} records matched your selection.
    </c:otherwise>
</c:choose>

5.2. Custom Logic Actions

It is important to note that the <c:if> and <c:when> actions have different semantics. A <c:if> action will always process its body content if its test condition evaluates to true. A <c:when> action will process its body content if it is the first one in a series of <c:when> actions whose test condition evaluates to true.

These semantic differences are enforced by the fact that only <c:when> actions can be used within the context of a mutually exclusive conditional execution (<c:choose> action). This clean separation of behavior also impacts the way custom logic actions (i.e. actions who render their bodies depending on the result of a test condition) should be designed. Ideally, the result associated with the evaluation of a custom logic action should be usable both in the context of a simple conditional execution, as well as in a mutually exclusive conditional execution.

The proper way to enable this is by simply having the custom logic action export the result of the test condition as a scoped variable. This boolean result can then be used as the test condition of a <c:when> action.

In the example below, the fictitious custom action <acme:fullMoon> tells whether or not a page is accessed during a full moon. The behavior of an if/then/else statement is made possible by having the result of the <acme:fullMoon> action exposed as a boolean scoped variable that is then used as the test condition in the <c:when> action.

<acme:fullMoon var="isFullMoon"/>
<c:choose>
    <c:when test="${isFullMoon}">
        ...
    </c:when>
    <c:otherwise>
        ...
    </c:otherwise>
</c:choose>

To facilitate the implementation of conditional actions where the boolean result is exposed as a Jakarta Server Pages scoped variable, class jakarta.servlet.jsp.jstl.core.ConditionalTagSupport has been defined in this specification.

5.3. <c:if>

Evaluates its body content if the expression specified with the test attribute is true.

Syntax

Syntax 1: Without body content

<c:if test="testCondition"
    var="varName" [scope="{page|request|session|application}"]/>

Syntax 2: With body content

<c:if test="testCondition"
        [var="varName"] [scope="{page|request|session|application}"]>
    body content
</c:if>
Body Content

Jakarta Server Pages content. If the test condition evaluates to true, the Jakarta Server Pages container processes the body content and then writes it to the current JspWriter.

Attributes
Name Dyn Type Description

test

true

boolean

The test condition that determines whether or not the body content should be processed.

var

false

String

Name of the exported scoped variable for the resulting value of the test condition. The type of the scoped variable is Boolean.

scope

false

String

Scope for var.

Constraints
  • If scope is specified, var must also be specified.

Description

If the test condition evaluates to true, the body content is evaluated by the Jakarta Server Pages container and the result is output to the current JspWriter.

5.4. <c:choose>

Provides the context for mutually exclusive conditional execution.

Syntax
<c:choose>
    body content (<when> and <otherwise> subtags)
</c:choose>
Body Content

Jakarta Server Pages content. The body content is processed by the Jakarta Server Pages container (at most one of the nested actions will be processed) and written to the current JspWriter.

Attributes

None.

Constraints
  • The body of the <c:choose> action can only contain:

    • White spaces
      May appear anywhere around the <c:when> and <c:otherwise> subtags.

    • 1 or more <c:when> actions
      Must all appear before <c:otherwise>

    • 0 or 1 <c:otherwise> action
      Must be the last action nested within <c:choose>

Description

The <c:choose> action processes the body of the first <c:when> action whose test condition evaluates to true. If none of the test conditions of nested <c:when> actions evaluates to true, then the body of an <c:otherwise> action is processed, if present.

5.5. <c:when>

Represents an alternative within a <c:choose> action.

Syntax
<c:when test="testCondition">
    body content
</c:when>
Body Content

Jakarta Server Pages content. If this is the first <c:when> action to evaluate to true within <c:choose>, the Jakarta Server Pages container processes the body content and then writes it to the current JspWriter.

Attributes
Name Dynamic Type Description

test

true

boolean

The test condition that determines whether or not the body content should be processed.

Constraints
  • Must have <c:choose> as an immediate parent.

  • Must appear before an <c:otherwise> action that has the same parent.

Description

Within a <c:choose> action, the body content of the first <c:when> action whose test condition evaluates to true is evaluated by the Jakarta Server Pages container, and the result is output to the current JspWriter.

5.6. <c:otherwise>

Represents the last alternative within a <c:choose> action.

Syntax
<c:otherwise>
    conditional block
</c:otherwise>
Body Content

Jakarta Server Pages content. If no <c:when> action nested within <c:choose> evaluates to true, the Jakarta Server Pages container processes the body content and then writes it to the current JspWriter.

Attributes

None.

Constraints
  • Must have <c:choose> as an immediate parent.

  • Must be the last nested action within <c:choose>.

Description

Within a <c:choose> action, if none of the nested <c:when> test conditions evaluates to true, then the body content of the <c:otherwise> action is evaluated by the Jakarta Server Pages container, and the result is output to the current JspWriter.

6. Iterator Actions: core tag library

Iterating over a collection of objects is a common occurrence in a Jakarta Server Pages page. Just as with conditional processing, a simple scriptlet can be used in such situations. However, this once again forces a page author to be knowledgeable in many aspects of the Java programming language (how to iterate on various collection types, having to cast the returned object into the proper type, proper use of the curly braces, etc.).

The Jakarta Standard Tag Library iterator actions simplify iterating over a wide variety of collections of objects.

6.1. Overview

The <c:forEach> action repeats its nested body content over the collection of objects specified by the items attribute. For example, the Jakarta Server Pages code below creates an HTML table with one column that shows the default display value of each item in the collection.

<table>
    <c:forEach var="customer" items="${customers}">
        <tr><td>${customer}</td></tr>
    </c:forEach>
</table>

The <c:forEach> action has the following features:

  • Supports all standard Java SE™ platform collection types.
    A page author therefore does not have to worry about the specific type of the collection of objects to iterate over (Collections of Objects to Iterate Over).

  • Exports an object that holds the current item of the iteration.
    Normally, each object exposed by <c:forEach> is an item of the underlying collection being iterated over. There are two exceptions to this to facilitate access to the information contained in arrays of primitive types, as well as in Map objects (see Map).

  • Exports an object that holds information about the status of the iteration (see Iteration Status).

  • Supports range attributes to iterate over a subset of the original collection (see Range Attributes).

  • Exposes an interface as well as a base implementation class.
    Developers can easily implement collaborating subtags as well as their own iteration tags (see Tag Collaboration).

<c:forEach> is the base iteration action in the Jakarta Standard Tag Library. It handles the most common iteration cases conveniently. Other iteration actions are also provided in the tag library to support specific, specialized functionality not handled by <c:forEach> (e.g. <c:forTokens> (<c:forTokens>) and <x:forEach> (<x:forEach>). Developers can also easily extend the behavior of this base iteration action to customize it according to an application’s specific needs.

6.1.1. Collections of Objects to Iterate Over

A large number of collection types are supported by <c:forEach>, including all implementations of java.util.Collection (includes List, LinkedList, ArrayList, Vector, Stack, Set), and java.util.Map (includes HashMap, Hashtable, Properties, Provider, Attributes).

Arrays of objects as well as arrays of primitive types (e.g. int) are also supported. For arrays of primitive types, the current item for the iteration is automatically wrapped with its standard wrapper class (e.g. Integer for int, Float for float, etc.).

Implementations of java.util.Iterator and java.util.Enumeration are supported as well but these must be used with caution. Iterator and Enumeration objects are not resettable so they should not be used within more than one iteration tag.

Deprecated: Finally, java.lang.String objects can be iterated over if the string represents a list of comma separated values (e.g. "Monday,Tuesday,Wednesday,Thursday,Friday").[3]

Absent from the list of supported types is java.sql.ResultSet (which includes javax.sql.RowSet). The reason for this is that the SQL actions described in Overview use the jakarta.servlet.jsp.jstl.sql.Result interface to access the data returned from an SQL query. Class jakarta.servlet.jsp.jstl.sql.ResultSupport allows business logic developers to easily convert a ResultSet object into a jakarta.servlet.jsp.jstl.sql.Result object, making life much easier for a page author that needs to manipulate the data returned from a SQL query.

6.1.2. Map

If the items attribute is of type java.util.Map, then the current item will be of type java.util.Map.Entry, which has the following two properties:

  • key - the key under which this item is stored in the underlying Map

  • value - the value that corresponds to this key

The following example uses <c:forEach> to iterate over the values of a Hashtable:

<c:forEach var="entry" items="${myHashtable}">
    Next element is ${entry.value}/>
</c:forEach>

6.1.3. Iteration Status

<c:forEach> also exposes information relative to the iteration taking place. The example below creates an HTML table with the first column containing the position of the item in the collection, and the second containing the name of the product.

<table>
    <c:forEach var="product" items="${products}"
            varStatus="status">
        <tr>
            <td>${status.count}</td>
            <td>${product.name}</td>
        </tr>
    </c:forEach>
</table>

See the Javadoc for details on the jakarta.servlet.jsp.jstl.core.LoopTagStatus interface exposed by the varStatus attribute.

6.1.4. Range Attributes

A set of range attributes is available to iterate over a subset of the collection of items. The begin and end indices can be specified, along with a step. If the items attribute is not specified, then the value of the current item is set to the integer value of the current index. In this example, i would take values from 100 to 110 (inclusive).

<c:forEach var="i" begin="100" end="110">
    ${i}
</c:forEach>

6.1.5. Tag Collaboration

Custom actions give developers the power to provide added functionality to a Jakarta Server Pages application without requiring the page author to use Java code. In this example, an item of the iteration is processed differently depending upon whether it is an odd or even element.

<c:forEach var="product" items="${products}" varStatus="status">
    <c:choose>
        <c:when test="${status.count % 2 == 0}">
            even item
        </c:when>
        <c:otherwise>
            odd item
        </c:otherwise>
    </c:choose>
</c:forEach>

If this type of processing is common, it could be worth providing custom actions that yield simpler code, as shown below.

<c:forEach var="product" items="${products}">
    <acme:even>
        even item
    </acme:even>
    <acme:odd>
        odd item
    </acme:odd>
</c:forEach>

In order to make this possible, custom actions like <acme:odd> and <acme:even> leverage the fact that <c:forEach> supports implicit collaboration via the interface jakarta.servlet.jsp.jstl.core.LoopTag.

The fact that <c:forEach> exposes an interface also means that other actions with iterative behavior can be developed using the same interface and will collaborate in the same manner with nested tags. Class jakarta.servlet.jsp.jstl.core.LoopTagSupport provides a solid base for doing this.

6.1.6. Deferred Values

The unified Expression Language supports the concept of deferred expressions (using the #{} syntax), i.e. expressions whose evaluation is deferred to application code (as opposed to immediate evaluation (using the ${} syntax) where the expression is evaluated immediately by the container). Deferred expressions are used mostly with Jakarta Server Faces, a component-based UI framework for the webtier.

In order for Jakarta Standard Tag Library iteration tags to support nested actions that access the iteration variable as a deferred-value, the items attribute must be specified as a deferred-value as well.

For example:

<c:forEach var="child" items="#{customer.children}">
    <h:inputText value="#{child.name}"/>
</c:forEach>

Because a deferred-value is specified for items, the iteration tag has access to the original expression and can make the iteration variable available as a deferred-value with the proper index into the items collection. This deferred value can then be evaluated properly by the code associated with the <h:inputText> component.

6.2. <c:forEach>

Repeats its nested body content over a collection of objects, or repeats it a fixed number of times.

Syntax

Syntax 1: Iterate over a collection of objects

<c:forEach  [var="varName"] items="collection"
            [varStatus="varStatusName"]
            [begin="begin"] [end="end"] [step="step"]>
    body content
</c:forEach>

Syntax 2: Iterate a fixed number of times

<c:forEach  [var="varName"]
            [varStatus="varStatusName"]
            begin="begin" end="end" [step="step"]>
    body content
</c:forEach>
Body Content

Jakarta Server Pages content. As long as there are items to iterate over, the body content is processed by the Jakarta Server Pages container and written to the current JspWriter.

Attributes
Name Dyn Type Description

var

false

String

Name of the exported scoped variable for the current item of the iteration. This scoped variable has nested visibility. Its type depends on the object of the underlying collection.

items

true

Any of the supported types described in Section "Description" below.

Collection of items to iterate over.

varStatus

false

String

Name of the exported scoped variable for the status of the iteration. Object exported is of type jakarta.servlet.jsp.jstl.core.LoopTagStatus. This scoped variable has nested visibility.

begin

true

int

If items specified:

Iteration begins at the item located at the specified index. First item of the collection has index 0.

If items not specified:

Iteration begins with index set at the value specified.

end

true

int

If items specified:

Iteration ends at the item located at the specified index (inclusive).

If items not specified:

Iteration ends when index reaches the value specified.

step

true

int

Iteration will only process every step items of the collection, starting with the first one.

Constraints
  • If specified, begin must be >= 0.

  • If end is specified and it is less than begin, the loop is simply not executed.

  • If specified, step must be >= 1

Null & Error Handling
  • If items is null, it is treated as an empty collection, i.e., no iteration is performed.

Description

If begin is greater than or equal to the size of items, no iteration is performed.

Collections Supported & Current Item

The data types listed below must be supported for items. With syntax 1, each object exposed via the var attribute is of the type of the object in the underlying collection, except for arrays of primitive types and maps (see below). With syntax 2, the object exported is of type Integer.

  • Arrays
    This includes arrays of objects as well as arrays of primitive types. For arrays of primitive types, the current item for the iteration is automatically wrapped with its standard wrapper class (e.g. Integer for int, Float for float, etc.)
    Elements are processed in their indexing order.

  • Implementation of java.util.Collection.
    An Iterator object is obtained from the collection via the iterator() method, and the items of the collection are processed in the order returned by that Iterator object.

  • Implementation of java.util.Iterator.
    Items of the collection are processed in the order returned by the Iterator object.

  • Implementation of java.util.Enumeration.
    Items of the collection are processed in the order returned by the Enumeration object.

  • Implementation of java.util.Map.
    The object exposed via the var attribute is of type Map.Entry.
    A Set view of the mappings is obtained from the Map via the entrySet() method, from which an Iterator object is obtained via the iterator() method. The items of the collection are processed in the order returned by that Iterator object.

  • String
    The string represents a list of comma separated values, where the comma character is the token delimiter. Tokens are processed in their sequential order in the string.

Deferred Values

When a deferred-value is specified for the items attribute, the tag handler now adds at each iteration a mapping for the var attribute into the Expression Language VariableMapper.

Below are some implementation notes illustrating how an iteration tag handler may process a deferred-value specified for the items attribute.

doStartTag()
    ...
    // 'items' is a deferred-value
    // Get the current Expression Language VariableMapper
    VariableMapper vm =
        jspContext.getELContext().getVariableMapper();
    // Create an expression to be assigned to the variable
    // specified in the 'var' attribute.
    // 'index' is an iteration counter kept by the tag handler.
    myimpl.IndexedExpression expr =
        new myimpl.IndexExpression(getItems(), index);
    // Assign the expression to the variable specified in
    // the 'var' attribute, so any reference to that variable
    // will be replaced by the expression in subsequent
    // Expression Language evaluations.
    oldMapping = vm.setVariable(getVar(), expr);
    ...

doEndTag()
    ...
    // restore the original state of the VariableMapper
    jspContext.getELContext().getVariableMapper().setVariable(
        getVar(), oldMapping);
    ...

The number of items referred to by the items attribute must be the same when Jakarta Server Faces creates the component tree and when Jakarta Server Pages executes the iteration tag. Undefined behavior will result if this is not the case.

6.3. <c:forTokens>

Iterates over tokens, separated by the supplied delimiters.

Syntax
<c:forTokens items="stringOfTokens" delims="delimiters"
        [var="varName"]
        [varStatus="varStatusName"]
        [begin="begin"] [end="end"] [step="step"]>
    body content
</c:forTokens>
Body Content

Jakarta Server Pages content. As long as there are items to iterate over, the body content is processed by the Jakarta Server Pages container and written to the current JspWriter.

Attributes
Name Dynamic Type Description

var

false

String

Name of the exported scoped variable for the current item of the iteration. This scoped variable has nested visibility.

items

true

String

String of tokens to iterate over.

delims

true

String

The set of delimiters (the characters that separate the tokens in the string).

varStatus

false

String

Name of the exported scoped variable for the status of the iteration. Object exported is of type jakarta.servlet.jsp.jstl.core.LoopTagStatus. This scoped variable has nested visibility.

begin

true

int

Iteration begins at the token located at the specified index. First token has index 0.

end

true

int

Iteration ends at the token located at the specified index (inclusive).

step

true

int

Iteration will only process every step tokens of the string, starting with the first one.

Constraints
  • If specified, begin must be >= 0.

  • If end is specified and it is less than begin, the loop is simply not executed.

  • If specified, step must be >= 1

Null & Error Handling
  • If items is null, it is treated as an empty collection, i.e., no iteration is performed.

  • If delims is null, items is treated as a single monolithic token. Thus, when delims is null, <c:forTokens> iterates exactly zero (if items is also null) or one time.

Description

The tokens of the string are retrieved using an instance of java.util.StringTokenizer with arguments items (the string to be tokenized) and delims (the delimiters).

Delimiter characters separate tokens. A token is a maximal sequence of consecutive characters that are not delimiters.

Deferred Values

See Section "Deferred Values" for <c:forEach>. Same comments apply here.

Linking, importing, and redirecting to URL resources are features often needed in Jakarta Server Pages. Since dealing with URLs can often be tricky, the Jakarta Standard Tag Library offers a comprehensive suite of URL-related actions to simplify these tasks.

By using the HTML <A> element, a page author can set a hypertext link as follows:

<a href="/register.jsp">Register</a>

If the link refers to a local resource and session tracking is enabled, it is necessary to rewrite the URL so session tracking can be used as a fallback, should cookies be disabled at the client.

Morevoer, if query string parameters are added to the URL, it is important that they be properly URL encoded. URL encoding refers to the process of encoding special characters in a string, according to the rules defined in RFC 2396. For example, a space must be encoded in a URL string as a '+':

http://acme.com/app/choose?country=Dominican+Republic

As shown in the following example, the combination of the <c:url> and <c:param> actions takes care of all issues related to URL rewriting and encoding: <c:url> rewrites a URL if necessary, and <c:param> transparently encodes query string parameters (both name and value).

<c:url value="http://acme.com/exec/register" var="myUrl">
    <c:param name="name" value="${param.name}"/>
    <c:param name="country" value="${param.country}"/>
</c:url>
<a href='<c:out value="${myUrl}"/>'>Register</a>

Another important feature of <c:url> is that it transparently prepends the context path to context-relative URLs. Assuming a context path of "/foo", the following example

<c:url value="/ads/logo.html"/>

yields the URL /foo/ads/logo.html.

7.2. Importing Resources

There is a wide variety of resources that a page author might be interested in including and/or processing within a Jakarta Server Pages page. For instance, the example below shows how the content of the README file at the FTP site of acme.com could be included within the page.

<c:import url="ftp://ftp.acme.com/README"/>

In the Jakarta Server Pages specification, a <jsp:include> action provides for the inclusion of static and dynamic resources located in the same context as the current page. This is a very convenient feature that is widely used by page authors.

However, <jsp:include> falls short in flexibility when page authors need to get access to resources that reside outside of the web application. In many situations, page authors have the need to import the content of Internet resources specified via an absolute URL. Moreover, as sites grow in size, they may have to be implemented as a set of web applications where importing resources across web applications is a requirement.

<jsp:include> also falls short in efficiency when the content of the imported resource is used as the source for a companion process/transformation action, because unnecessary buffering occurs. In the example below, the <acme:transform> action uses the content of the included resource as the input of its transformation. <jsp:include> reads the content of the response, writes it to the body content of the enclosing <acme:transform>, which then re-reads the exact same content. It would be more efficient if <acme:transform> could access the input source directly and avoid the buffering involved in the body content of <acme:transform>.

<acme:transform>
    <jsp:include page="/exec/employeesList"/>
</acme:transform>

The main motivation behind <c:import> is to address these shortcomings by providing a simple, straightforward mechanism to access resources that can be specified via a URL. If accessing a resource requires specifying more arguments, then a protocol specific action (e.g. an <http> action) should be used for that purpose. The Jakarta Standard Tag Library does not currently address these protocol-specific elements but may do so in future releases.

7.2.1. URL

The url attribute is used to specify the URL of the resource to import. It can either be an absolute URL (i.e. one that starts with a protocol followed by a colon), a relative URL used to access a resource within the same context, or a relative URL used to access a resource within a foreign context. The three different types of URL are shown in the sample code below.

<%-- import a resource with an absolute URL --%>
<c:import url="http://acme.com/exec/customers?country=Japan"/>

<%-- import a resource with a relative URL - same context --%>
<c:import url="/copyright.html"/>

<%-- import a resource with a relative URL - foreign context --%>
<c:import url="/logo.html" context="/master"/>

7.2.2. Exporting an object: String or Reader

By default, the content of an imported resource is included inline into the Jakarta Server Pages page.

It is also possible to make the content of the resource available in two different ways: as a String object (attribute var), or as a Reader object (attribute varReader). Process or Transform tags can then access the resource’s content through that exported object as shown in the following example.

<%-- Export the content of the URL resource as a String --%>
<c:import url="http://acme.com/exec/customers?country=USA"
          var="customers"/>
<acme:notify in="${customers}"/>

<%-- Export the content of the URL resource as a Reader --%>

<c:import url="http://acme.com/exec/customers?country=USA"
          varReader="customers">
    <acme:notify in="${customers}"/>
</c:import>

Exporting the resource as a String object caches its content and makes it reusable.

If the imported content is large, some performance benefits may be achieved by exporting it as a Reader object since the content can be accessed directly without any buffering. However, the performance benefits are not guaranteed since the reader’s support is implementation dependent. It is also important to note that the varReader scoped variable has nested visibility; it can only be accessed within the body content of <c:import>.

7.2.3. URL Encoding

Just as with <c:url>, <c:param> can be nested within <c:import> to encode query string parameters.

7.2.4. Networking Properties

If the web container executes behind a firewall, some absolute URL resources may be inaccessible when using <c:import>. To provide access to these resources, the JVM of the container should be started with the proper networking properties (e.g. proxyHost, proxyPort). More details can be found in the Java 2 SDK, Standard Edition Documentation (Networking Features — Networking Properties).

7.3. HTTP Redirect

<c:redirect> completes the arsenal of URL related actions to support an HTTP redirect to a specific URL. For example:

<c:redirect url="http://acme.com/register"/>

7.4. <c:import>

Imports the content of a URL-based resource.

Syntax

Syntax 1: Resource content inlined or exported as a String object

<c:import url="url" [context="context"]
        [var="varName"] [scope="{page|request|session|application}"]
        [charEncoding="charEncoding"]>
    optional body content for <c:param> subtags
</c:import>

Syntax 2: Resource content exported as a Reader object

<c:import url="url" [context="context"]
        varReader="varReaderName"
        [charEncoding="charEncoding"]>
    body content where varReader is consumed by another action
</c:import>
Body Content

Jakarta Server Pages content. The body content is processed by the Jakarta Server Pages container and the result is written to the current JspWriter.

Attributes
Name Dynamic Type Description

url

true

String

The URL of the resource to import.

context

true

String

Name of the context when accessing a relative URL resource that belongs to a foreign context.

var

false

String

Name of the exported scoped variable for the resource’s content. The type of the scoped variable is String.

scope

false

String

Scope for var.

charEncoding

true

String

Character encoding of the content at the input resource.

varReader

false

String

Name of the exported scoped variable for the resource’s content. The type of the scoped variable is Reader.

Null & Error Handling
  • If url is null, empty, or invalid, a JspException is thrown.

  • If charEncoding is null or empty, it is considered missing.

  • For internal resources:

    1. If a RequestDispatcher cannot be found for the resource, throw a JspException with the resource path included in the message.

    2. Otherwise, if the RequestDispatcher.include() method throws an IOException or RuntimeException, throw a JspException with the caught exception as the root cause.

    3. Otherwise, if the RequestDispatcher.include() method throws a ServletException, look for a root cause.

      1. If there’s a root cause, throw a JspException with the root cause message included in the message and the original root cause as the JspException root cause.

      2. Otherwise, same as 2).

    4. Otherwise, if the resource invoked through RequestDispatcher.include() method sets a response status code other than 2xx (i.e. 200-299, the range of success codes in the HTTP response codes), throw a JspException with the path and status code in the message.

  • For external resources

    • If the URLConnection class throws an IOException or a RuntimeException, throw a JspException with the message from the original exception included in the message and the original exception as the root cause.

    • For an HttpURLConnection, if the response status code is other than 2xx (i.e. 200-299, the range of success codes in the HTTP response codes), throw a JspException with the path and status code in the message.

Description

Using syntax 1, the content of the resource is by default written to the current JspWriter. If var is specified, the content of the resource is instead exposed as a String object.

Using syntax 2, the content of the resource is exported as a Reader object. The use of the varReader attribute comes with some restrictions.

It is the responsibility of the <c:import> tag handler to ensure that if it exports a Reader, this Reader is properly closed by the time the end of the page is reached[4]. Because of this requirement, the Jakarta Standard Tag Library defines the exported Reader as having nested visibility: it may not currently be accessed after the end-tag for the <c:import> action[5]. Implementations that use the tag-extension API will likely need to implement TryCatchFinally with their <c:import> tag handlers and close the exported Reader in doFinally().

It is also illegal to use nested <c:param> tags with syntax 2. Since the exposed Reader must be immediately available to the action’s body, the connection to the resource must be established within the start element of the action. It is therefore impossible for nested <c:param> actions to modify the URL of the resource to be accessed, thus their illegality with syntax 2. In such a situation, <c:url> may be used to build a URL with query string parameters[6]. <c:import> will remove any session id information if necessary (see <c:url>).

Character Encoding

<c:import> exposes a String or Reader object, both of which are sequences of text characters. It is possible to specify the character encoding of the input resource via the charEncoding attribute. The values supported for charEncoding are the same as the ones supported by the constructor of the Java class InputStreamReader.

If the character encoding is not specified, the following rules apply:

  • If URLConnection.getContentType() has a non-null result, the character set is retrieved from URLConnection.getContentType() by parsing this method’s result according to RFC 2045 (section 5.1).

  • If this method’s result does not include a character set, or if the character set causes InputStreamReader(InputStream in, String charsetName) to throw an UnsupportedEncodingException, then use ISO-8859-1 (which is the default value of charset for the contentType attribute of the Jakarta Server Pages page directive).

Note that the charEncoding attribute should normally only be required when accessing absolute URL resources where the protocol is not HTTP, and where the encoding is not ISO-8859-1.

Also, when dealing with relative URLs and the HTTP protocol, if the target resource declares a content encoding but proceeds to write a character invalid in that encoding, the treatment of that character is undefined.

Relative and Absolute URLs

The exact semantics of the <c:import> tag depends on what type of URL is being accessed.

Relative URL – same context

This is processed in the exact same way as the include action of the Jakarta Server Pages specification (<jsp:include>). The resource belongs to the same web application as the including page and it is specified as a relative URL.

As specified in the Jakarta Server Pages specification, a relative URL may either be a context-relative path, or a page-relative path. A context-relative path is a path that starts with a "/". It is to be interpreted as relative to the application to which the Jakarta Server Pages page belongs. A page-relative path is a path that does not start with a "/". It is to be interpreted as relative to the current Jakarta Server Pages page, as defined by the rules of inclusion of the <jsp:include> action in the Jakarta Server Pages specification.

The semantics of importing a resource specified with a relative URL in the same context are the same as an include performed by a RequestDispatcher as defined in the Servlet specification. This means that the whole environment of the importing page is available to the target resource (including request and session attributes, as well as request parameters of the importing page).

Relative URL – foreign context

The resource belongs to a foreign context (web application) hosted under the same container as the importing page. The context name for the resource is specified via attribute context.

The relative URL must be context-relative (i.e. must start with a "/") since the including page does not belong to the same context. Similarly, the context name must also start with a "/".

The semantics of importing a resource specified with a relative URL in a foreign context are the same as an include performed by a RequestDispatcher on a foreign context as defined in the Servlet specification. This means that only the request environment of the importing page is available to the target resource.

It is important to note that importing resources in foreign contexts may not work in all containers. A security conscious environment may not allow access to foreign contexts. As a workaround, a foreign context resource can also be accessed using an absolute URL. However, it is more efficient to use a relative URL because the resource is then accessed using RequestDispatcher defined by the Servlet API.

Relative URL – query parameter aggregation rules

The query parameter aggregation rules work the same way they do with <jsp:include>; the original parameters are augmented with the new parameters, with new values taking precedence over existing values when applicable. The scope of the new parameters is the import call; the new parameters (and values) will not apply after the import. The behavior is therefore the same as the one defined for the include() method of RequestDispatcher in the Servlet specification.

Absolute URL

Absolute URLs are retrieved as defined by the java.net.URL and java.net.URLConnection classes. The <c:import> action therefore supports at a minimum the protocols offered in the Java SE 1.2 platform for absolute URLs. More protocols can be available to a web application, but this will depend on the the class libraries made available to the web application by the platform the container runs on.

When using an absolute URL to import a resource, none of the current execution environment (e.g. request and session attributes) is made available to the target resource, even if that absolute URL resolves to the same host and context path. Therefore, the request parameters of the importing page are not propagated to the target absolute URL.

When importing an external resource using the HTTP protocol, <c:import> behaves according to the semantics of a GET request sent via the java.net.HttpURLConnection class, with setFollowRedirects set to true.

7.5. <c:url>

Builds a URL with the proper rewriting rules applied.

Syntax

Syntax 1: Without body content

<c:url value="value" [context="context"]
        [var="varName"] [scope="{page|request|session|application}"]/>

Syntax 2: With body content to specify query string parameters

<c:url value="value" [context="context"]
        [var="varName"] [scope="{page|request|session|application}"]>
    <c:param> subtags
</c:url>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dynamic Type Description

value

true

String

URL to be processed.

context

true

String

Name of the context when specifying a relative URL resource that belongs to a foreign context.

var

false

String

Name of the exported scoped variable for the processed url. The type of the scoped variable is String.

scope

false

String

Scope for var.

Description

<c:url> processes a URL and rewrites it if necessary. Only relative URLs are rewritten. Absolute URLs are not rewritten to prevent situations where an external URL could be rewritten and expose the session ID. A consequence is that if a page author wants session tracking, only relative URLs must be used with <c:url> to link to local resources.

The rewriting must be performed by calling method encodeURL() of the Servlet API.

If the URL contains characters that should be encoded (e.g. space), it is the user’s responsibility to encode them.

The URL must be either an absolute URL starting with a scheme (e.g. "http://server/context/page.jsp") or a relative URL as defined by Jakarta Server Pages in JSP.2.2.1 "Relative URL Specification". As a consequence, an implementation must prepend the context path to a URL that starts with a slash (e.g. "/page2.jsp") so that such URLs can be properly interpreted by a client browser.

Specifying a URL in a foreign context is possible through the context attribute. The URL specified must must start with a / (since this is a context-relative URL). The context name must also start with a / (since this is a standard way to identify a context).

Because the URL built by this action may include session information as a path parameter, it may fail if used with RequestDispatcher of the Servlet API. The consumer of the rewritten URL should therefore remove the session ID information prior to calling RequestDispatcher. This situation is properly handled in <c:import>.

By default, the result of the URL processing is written to the current JspWriter. It is also possible to export the result as a Jakarta Server Pages scoped variable defined via the var and scope attributes.

<c:param> subtags can also be specified within the body of <c:url> for adding to the URL query string parameters, which will be properly encoded if necessary.

7.6. <c:redirect>

Sends an HTTP redirect to the client.

Syntax

Syntax 1: Without body content

<c:redirect url="value" [context="context"]/>

Syntax 2: With body content to specify query string parameters

<c:redirect url="value" [context="context"]>
    <c:param> subtags
</c:redirect>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

url

true

String

The URL of the resource to redirect to.

context

true

String

Name of the context when redirecting to a relative URL resource that belongs to a foreign context.

Description

This action sends an HTTP redirect response to the client and aborts the processing of the page by returning SKIP_PAGE from doEndTag().

The URL must be either an absolute URL starting with a scheme (e.g. "http://server/context/page.jsp") or a relative URL as defined by Jakarta Server Pages in JSP.2.2.1 "Relative URL Specification". As a consequence, an implementation must prepend the context path to a URL that starts with a slash (e.g. "/page2.jsp") if the behavior is implemented using the HttpServletResponse.sendRedirect() method.

Redirecting to a resource in a foreign context is possible through the context attribute. The URL specified must must start with a "/" (since this is a context-relative URL). The context name must also start with a "/" (since this is a standard way to identify a context).

<c:redirect> follows the same rewriting rules as defined for <c:url>.

7.7. <c:param>

Adds request parameters to a URL. Nested action of <c:import>, <c:url>, <c:redirect>.

Syntax

Syntax 1: Parameter value specified in attribute "value"

<c:param name="name" value="value"/>

Syntax 2: Parameter value specified in the body content

<c:param name="name">
    parameter value
</c:param>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dynamic Type Description

name

true

String

Name of the query string parameter.

value

true

String

Value of the parameter.

Null & Error Handling
  • If name is null or empty, no action is performed. It is not an error.

  • If value is null, it is processed as an empty value.

Description

Nested action of <c:import>, <c:url>, <c:redirect> to add request parameters to a URL. <c:param> also URL encodes both name and value.

One might argue that this is redundant given that a URL can be constructed to directly specify the query string parameters. For example:

<c:import url="/exec/doIt">
    <c:param name="action" value="register"/>
</c:import>

is the same as:

<c:import url="/exec/doIt?action=register"/>

It is indeed redundant, but is consistent with <jsp:include>, which supports nested <jsp:param> sub-elements. Moreover, it has been designed such that the attributes name and value are automatically URL encoded.

8. Internationalization (i18n) Actions: I18n-capable formatting tag library

With the explosion of application development based on web technologies, and the deployment of such applications on the Internet, applications must be able to adapt to the languages and formatting conventions of their clients. This means that page authors must be able to tailor page content according to the client’s language and cultural formatting conventions. For example, the number 345987.246 should be formatted as 345 987,246 for France, 345.987,246 for Germany, and 345,987.246 for the U.S.

The process of designing an application (or page content) so that it can be adapted to various languages and regions without requiring any engineering changes is known as internationalization, or i18n for short. Once a web application has been internationalized, it can be adapted for a number of regions or languages by adding locale-specific components and text. This process is known as localization.

There are two approaches to internationalizing a web application:

  • Provide a version of the Jakarta Server Pages in each of the target locales and have a controller servlet dispatch the request to the appropriate page (depending on the requested locale). This approach is useful if large amounts of data on a page or an entire web application need to be internationalized.

  • Isolate any locale-sensitive data on a page (such as error messages, string literals, or button labels) into resource bundles, and access the data via i18n actions, so that the corresponding translated message is fetched automatically and inserted into the page.

The Jakarta Standard Tag Library i18n-capable formatting actions support either approach: They assist page authors with creating internationalized page content that can be localized into any locale available in the Jakarta Server Pages container (this addresses the second approach), and allow various data elements such as numbers, currencies, dates and times to be formatted and parsed in a locale-sensitive or customized manner (this may be used in either approach).

The Jakarta Standard Tag Library’s i18n actions are covered in this chapter. The formatting actions are covered in Formatting Actions: I18n-capable formatting tag library.

8.1. Overview

There are three key concepts associated with internationalization: locale, resource bundle, and basename.

A locale represents a specific geographical, political, or cultural region. A locale is identified by a language code, along with an optional country code[7].

Note that the semantics of locales in the Jakarta Standard Tag Library are the same as the ones defined by the class java.util.Locale. A consequence of this is that, as of Java SE 1.4, new language codes defined in ISO 639 (e.g. he, yi, id) will be returned as the old codes (e.g. iw, ji, in). See the documentation of the java.util.Locale class for more details.

A resource bundle contains locale-specific objects. Each message in a resource bundle is associated with a key. Since the set of messages contained in a resource bundle can be localized for many locales, the resource bundles that translate the same set of messages are identified by the same basename. A specific resource bundle is therefore uniquely identified by combining its basename with a locale.

For instance, a web application could define the registration resource bundles with basename Registration to contain the messages associated with the registration portion of the application. Assuming that French and English are the only languages supported by the application, there will be two resource bundles: Registration_fr (French language) and Registration_en (English language). Depending on the locale associated with the client request, the key "greeting" could be mapped to the message "Bonjour" (French) or "Hello" (English).

8.1.1. <fmt:message>

It is possible to internationalize the Jakarta Server Pages of a web application simply by using the <fmt:message> action as shown below:

<fmt:message key="greeting"/>

In this case, <fmt:message> leverages the default i18n localization context, making it extremely simple for a page author to internationalize Jakarta Server Pages.

<fmt:message> also supports compound messages, i.e. messages that contain one or more variables. Parameter values for these variables may be supplied via one or more <fmt:param> subtags (one for each parameter value). This procedure is referred to as parametric replacement.

<fmt:message key="athletesRegistered">
    <fmt:param>
        <fmt:formatNumber value="${athletesCount}"/>
    </fmt:param>
</fmt:message>

Depending on the locale, this example could print the following messages:

 french: Il y a 10 582 athletes enregistres.
english: There are 10,582 athletes registered.

8.2. I18n Localization Context

I18n actions use an i18n localization context to localize their data. An i18n localization context contains two pieces of information: a resource bundle and the locale for which the resource bundle was found.

An i18n action determine its i18n localization context in one of several ways, which are described in order of precedence:

  • <fmt:message> bundle attribute
    If attribute bundle is specified in <fmt:message>, the i18n localization context associated with it is used for localization.

  • <fmt:bundle> action
    If <fmt:message> actions are nested inside a <fmt:bundle> action, the i18n localization context of the enclosing <fmt:bundle> action is used for localization. The <fmt:bundle> action determines the resource bundle of its i18n localization context according to the resource bundle determination algorithm in Determinining the Resource Bundle for an i18n Localization Context, using the basename attribute as the resource bundle basename.

  • I18n default localization context
    The i18n localization context whose resource bundle is to be used for localization is specified via the jakarta.servlet.jsp.jstl.fmt.localizationContext configuration setting (see I18n Localization Context). If the configuration setting is of type jakarta.servlet.jsp.jstl.fmt.LocalizationContext its resource bundle component is used for localization. Otherwise, the configuration setting is of type String, and the action establishes its own i18n localization context whose resource bundle component is determined according to the resource bundle determination algorithm in Determinining the Resource Bundle for an i18n Localization Context, using the configuration setting as the resource bundle basename.

The example below shows how the various localization contexts can be established to define the resource bundle used for localization.

<%-- Use configuration setting --%>
<fmt:message key="Welcome" />

<fmt:setBundle basename="Errors" var="errorBundle" />
<fmt:bundle basename="Greetings">
    <%-- Localization context established by
         parent <fmt:bundle> tag --%>
    <fmt:message key="Welcome" />
    <%-- Localization context established by attribute bundle --%>
    <fmt:message key="WrongPassword" bundle="${errorBundle}" />
</fmt:bundle>

8.2.1. Preferred Locales

If the resource bundle of an i18n localization context needs to be determined, it is retrieved from the web application’s resources according to the algorithm described in Section Determinining the Resource Bundle for an i18n Localization Context. This algorithm requires two pieces of information: the basename of the resource bundle (as described in the previous section) and the preferred locales.

The method for setting the preferred locales is characterized as either application-based or browser-based.

Application-based locale setting has priority over browser-based locale setting. In this mode, the locale is set via the jakarta.servlet.jsp.jstl.fmt.locale configuration setting (see Locale). Setting the locale this way is useful in situations where an application lets its users pick their preferred locale and then sets the scoped variable accordingly. This may also be useful in the case where a client’s preferred locale is retrieved from a database and installed for the page using the <fmt:setLocale> action.

The <fmt:setLocale> action may be used to set the jakarta.servlet.jsp.jstl.fmt.locale configuration variable as follows:

<fmt:setLocale value="en_US" />

In the browser-based locale setting, the client determines via its browser settings which locale(s) should be used by the web application. The action retrieves the client’s locale preferences by calling ServletRequest.getLocales() on the incoming request. This returns a list of the locales (in order of preference) that the client wants to use.

Whether application- or browser-based locale setting is used, an ordered list of preferred locales is fed into the algorithm described in section Determinining the Resource Bundle for an i18n Localization Context to determine the resource bundle for an i18n localization context.

8.3. Determinining the Resource Bundle for an i18n Localization Context

Given a basename and an ordered set of preferred locales, the resource bundle for an i18n localization context is determined according to the algorithm described in this section.

Tthis algorithm is also exposed as a general convenience method in the jakarta.servlet.jsp.jstl.fmt.LocaleSupport class so that it may be used by any tag handler implementation that needs to produce localized messages. For example, this is useful for exception messages that are intended directly for user consumption on an error page.

8.3.1. Resource Bundle Lookup

Localization in the Jakarta Standard Tag Library is based on the same mechanisms offered in the Java SE platform. Resource bundles contain locale-specific objects, and when an i18n action requires a locale-specific resource, it simply loads it from the appropriate resource bundle.

The algorithm of Resource Bundle Determination Algorithm describes how the proper resource bundle is determined. This algorithm calls for a resource bundle lookup, where an attempt is made at fetching a resource bundle associated with a specific basename and locale.

The Jakarta Standard Tag Library leverages the semantics of the java.util.ResourceBundle method

getBundle(String basename, java.util.Locale locale)

for resource bundle lookup, with one important modification.

As stated in the documentation for ResourceBundle, a resource bundle lookup searches for classes and properties files with various suffixes on the basis of:

  1. The specified locale

  2. The current default locale as returned by Locale.getDefault()

  3. The root resource bundle (basename)

In the Jakarta Standard Tag Library, the search is limited to the first level; i.e. the specified locale. Steps 2 and 3 are removed so that other locales may be considered before applying the Jakarta Standard Tag Library fallback mechanism described in Resource Bundle Determination Algorithm. Only if no fallback mechanism exists, or the fallback mechanism fails to determine a resource bundle, is the root resource bundle considered.

Resource bundles are therefore searched in the following order:

basename + "" + language + "" + country + "" + variant
basename + "
" + language + "" + country
basename + "
" + language

8.3.2. Resource Bundle Determination Algorithm

Notes:

  • When there are multiple preferred locales, they are processed in the order they were returned by ServletRequest.getLocales().

  • The algorithm stops as soon as a resource bundle has been selected for the localization context.

Step 1: Find a match within the ordered set of preferred locales

A resource bundle lookup (see Resource Bundle Lookup) is performed for each one of the preferred locales until a match is found. If a match is found, the locale that led to the match and the matched resource bundle are stored in the i18n localization context.

Step 2: Find a match with the fallback locale

A resource bundle lookup (see Resource Bundle Lookup) is performed for the fallback locale specified in the jakarta.servlet.jsp.jstl.fmt.fallbackLocale configuration setting. If a match is found, the fallback locale and the matched resource bundle are stored in the i18n localization context.

If no match is found following the above two steps, an attempt is made to load the root resource bundle with the given basename. If such a resource bundle exists, it is used as the resource bundle of an i18n localization context that does not have any locale. Otherwise, the established i18n localization context contains neither a resource bundle nor a locale. It is then up to the i18n action relying on this i18n localization context for the localization of its data to take a proper corrective action.

It is important to note that this algorithm gives higher priority to a language match over an exact match that would have occurred further down the list of preferred locales. For example, if the browser-based locale settings are "en" and "fr_CA", with resource bundles "Messages_en" and "Messages_fr_CA", the Messages_en bundle will be selected as the resource bundle for the localization context.

The definition of a fallback locale along with its associated resource bundles is the only portable way a web application can ensure the proper localization of all its internationalized pages. The algorithm of this section never considers the default locale associated with the Java runtime of the container because this would result in a non-portable behavior.

The behavior is implementation-specific if the set of available resource bundles changes during execution of the page. Implementations may thus cache whatever information they deem necessary to improve the performance of the algorithm presented in this section.

8.3.3. Examples

The following examples demonstrate how the resource bundle is determined for an i18n localization context.

Example 1

Settings
Basename: Resources
Ordered preferred locales: en_GB, fr_CA
Fallback locale: fr_CA
Resource bundles: Resources_en, Resources_fr_CA

Algorithm Trace
Step 1: Find a match within the ordered set of preferred locales
     en_GB match with Resources_en

Result
Resource bundle selected: Resources_en
Locale: en_GB

Example 2

Settings
Basename: Resources
Ordered preferred locales: de, fr
Fallback locale: en
Resource bundles: Resources_en

Algorithm Trace
Step 1: Find a match within the ordered set of preferred locales
     de no match
     fr no match

Step 2: Find a match with the fallback locale
     en exact match with Resources_en

Result
Resource bundle selected: Resources_en
Locale: en

Example 3

Settings
Basename: Resources
Ordered preferred locales: ja, en_GB, en_US, en_CA, fr
Fallback locale: en
Resource bundles: Resources_en, Resources_fr, Resources_en_US

Algorithm Trace
Step 1: Find a match within the ordered set of preferred locales
     ja no match
     en_GB match with Resources_en

Result

Resource bundle selected: Resources_en
Locale: en_GB

Example 4

Settings Basename: Resources
Ordered preferred locales: fr, sv
Fallback locale: en
Resource bundles: Resources_fr_CA, Resources_sv, Resources_en

Algorithm Trace

Step 1: Find a match within the ordered set of preferred locales
     fr no match
     sv match with Resources_sv

Result
Resource bundle selected: Resources_sv
Locale: sv

This example shows that whenever possible, a resource bundle for a specific language and country ( Resources_fr_CA ) should be backed by a resource bundle covering just the language ( Resources_fr). If the country-specific differences of a language are too significant for there to be a language-only resource bundle, it is expected that clients will specify both a language and a country as their preferred language, in which case an exact resource bundle match will be found.

8.4. Response Encoding

Any i18n action that establishes a localization context is responsible for setting the response’s locale of its page, unless the localization context that was established does not have any locale. This is done by calling method ServletResponse.setLocale() with the locale of the localization context. Unless a response character encoding has been explicitly defined by other Jakarta Server Pages elements (or by direct calls to the Servlet API), calling setLocale() also sets the character encoding for the response (see the Jakarta Server Pages and Servlet specifications for details).

This assumes that the response is buffered with a big enough buffer size, since ServletResponse.setLocale() must be called before ServletResponse.getWriter() in order for the specified locale to affect the construction of the writer.

More specifically, the response’s setLocale() method is always called by the <fmt:setLocale> action (see <fmt:setLocale>). In addition, it is called by the following actions:

After an action has called ServletResponse.setLocale(), if a session exists and has not been invalidated, it must determine the character encoding associated with the response locale (by calling ServletResponse.getCharacterEncoding() ) and store it in the scoped variable jakarta.servlet.jsp.jstl.fmt.request.charset in session scope. This attribute may be used by the <fmt:requestEncoding> action (see <fmt:requestEncoding>) in a page invoked by a form included in the response to set the request charset to the same as the response charset. This makes it possible for the container to decode the form parameter values properly, since browsers typically encode form field values using the response’s charset.

The rules related to the setting of an HTTP response character encoding, Content-Language header, and Content-Type header are clearly defined in the Servlet specification. To avoid any ambiguity, the Jakarta Standard Tag Library and Jakarta Server Pages specifications define behavior related to a response’s locale and character encoding exclusively in terms of Servlet API calls.

It is therefore important to note that, as defined in the Servlet spec, a call to ServletResponse.setLocale() modifies the character encoding of the response only if it has not already been set explicitely by calls to ServletResponse.setContentType() (with CHARSET specified) or ServletResponse.setCharacterEncoding().

Page authors should consult the Jakarta Server Pages specification to understand how page directives related to locale and character encoding setting translate into Servlet API calls, and how they impact the final response settings.

8.5. <fmt:setLocale>

Stores the specified locale in the jakarta.servlet.jsp.jstl.fmt.locale configuration variable.

Syntax
<fmt:setLocale value="locale"
            [variant="variant"]
            [scope="{page|request|session|application}"]/>
Body Content

Empty.

Attributes
Name Dynamic Type Description

value

true

String or

java.util.Locale

A String value is interpreted as the printable representation of a locale, which must contain a two-letter (lower-case) language code (as defined by ISO-639), and may contain a two-letter (upper-case) country code (as defined by ISO-3166). Language and country codes must be separated by hyphen ('-') or underscore ('_').

variant

true

String

Vendor- or browser-specific variant.

See the java.util.Locale Javadocs for more information on variants.

scope

false

String

Scope of the locale configuration variable.

Null & Error Handling
  • If value is null or empty, use the runtime default locale.

Description

The <fmt:setLocale> action stores the locale specified by the value attribute in the jakarta.servlet.jsp.jstl.fmt.locale configuration variable in the scope given by the scope attribute. If value is of type java.util.Locale , variant is ignored.

As a result of using this action, browser-based locale setting capabilities are disabled. This means that if this action is used, it should be declared at the beginning of a page, before any other i18n-capable formatting actions.

8.6. <fmt:bundle>

Creates an i18n localization context to be used by its body content.

Syntax
<fmt:bundle basename="basename"
            [prefix="prefix"]>
    body content
</fmt:bundle>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content and then writes it to the current JspWriter. The action ignores the body content.

Attributes
Name Dynamic Type Description

basename

true

String

Resource bundle base name. This is the bundle’s fully-qualified resource name, which has the same form as a fully-qualified class name, that is, it uses "." as the package component separator and does not have any file type (such as ".class" or ".properties") suffix.

prefix

true

String

Prefix to be prepended to the value of the message key of any nested <fmt:message> action.

Null & Error Handling
  • If basename is null or empty, or a resource bundle cannot be found, the null resource bundle is stored in the i18n localization context.

Description

The <fmt:bundle> action creates an i18n localization context and loads its resource bundle into that context. The name of the resource bundle is specified with the basename attribute.

The specific resource bundle that is loaded is determined according to the algorithm presented in Resource Bundle Determination Algorithm.

The scope of the i18n localization context is limited to the action’s body content.

The prefix attribute is provided as a convenience for very long message key names. Its value is prepended to the value of the message key of any nested <fmt:message> actions.

For example, using the prefix attribute, the key names in:

<fmt:bundle basename="Labels">
    <fmt:message key="com.acme.labels.firstName"/>
    <fmt:message key="com.acme.labels.lastName"/>
</fmt:bundle>

may be abbreviated to:

<fmt:bundle basename="Labels" prefix="com.acme.labels.">
    <fmt:message key="firstName"/>
    <fmt:message key="lastName"/>
</fmt:bundle>

8.7. <fmt:setBundle>

Creates an i18n localization context and stores it in the scoped variable or the jakarta.servlet.jsp.jstl.fmt.localizationContext configuration variable.

Syntax
<fmt:setBundle basename="basename"
               [var="varName"]
               [scope="{page|request|session|application}"]/>
Body Content

Empty.

Attributes
Name Dynamic Type Description

basename

true

String

Resource bundle base name. This is the bundle’s fully-qualified resource name, which has the same form as a fully-qualified class name, that is, it uses "." as the package component separator and does not have any file type (such as ".class" or ".properties") suffix.

var

false

String

Name of the exported scoped variable which stores the i18n localization context of type jakarta.servlet.jsp.jstl.fmt.LocalizationContext.

scope

false

String

Scope of var or the localization context configuration variable.

Null & Error Handling
  • If basename is null or empty, or a resource bundle cannot be found, the null resource bundle is stored in the i18n localization context.

Description

The <fmt:setBundle> action creates an i18n localization context and loads its resource bundle into that context. The name of the resource bundle is specified with the basename attribute.

The specific resource bundle that is loaded is determined according to the algorithm presented in Resource Bundle Determination Algorithm.

The i18n localization context is stored in the scoped variable whose name is given by var. If var is not specified, it is stored in the jakarta.servlet.jsp.jstl.fmt.localizationContext configuration variable, thereby making it the new default i18n localization context in the given scope.

8.8. <fmt:message>

Looks up a localized message in a resource bundle.

Syntax

Syntax 1: without body content

<fmt:message key="messageKey"
             [bundle="resourceBundle"]
             [var="varName"]
             [scope="{page|request|session|application}"]/>

Syntax 2: with a body to specify message parameters

<fmt:message key="messageKey"
             [bundle="resourceBundle"]
             [var="varName"]
             [scope="{page|request|session|application}"]>
    <fmt:param> subtags
</fmt:message>

Syntax 3: with a body to specify key and optional message parameters

<fmt:message [bundle="resourceBundle"]
             [var="varName"]
             [scope="{page|request|session|application}"]>
    key
    optional <fmt:param> subtags
</fmt:message>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

key

true

String

Message key to be looked up.

bundle

true

LocalizationContext

Localization context in whose resource bundle the message key is looked up.

var

false

String

Name of the exported scoped variable which stores the localized message.

scope

false

String

Scope of var.

Constraints
  • If scope is specified, var must also be specified.

Null & Error Handling
  • If key is null or empty, the message is processed as if undefined; that is, an error message of the form "??????" is produced.

  • If the i18n localization context that this action determines does not have any resource bundle, an error message of the form "???<key>???" is produced

Description

The <fmt:message> action looks up the localized message corresponding to the given message key.

The message key may be specified via the key attribute or from the tag’s body content. If this action is nested inside a <fmt:bundle> action, and the parent <fmt:bundle> action contains a prefix attribute, the specified prefix is prepended to the message key.

<fmt:message> uses the resource bundle of the i18n localization context determined according to I18n Localization Context.

If the given key is not found in the resource bundle, or the i18n localization context does not contain any resource bundle, the result of the lookup is an error message of the form "???<key>???" (where <key> is the name of the undefined message key).

If the message corresponding to the given key is compound, that is, contains one or more variables, it may be supplied with parameter values for these variables via one or more <fmt:param> subtags (one for each parameter value). This procedure is referred to as parametric replacement. Parametric replacement takes place in the order of the <fmt:param> subtags.

In the presence of one or more <fmt:param> subtags, the message is supplied to the java.text.MessageFormat method applyPattern(), and the values of the <fmt:param> tags are collected in an Object[] and supplied to the java.text.MessageFormat method format(). The locale of the java.text.MessageFormat is set to the appropriate localization context locale before applyPattern() is called. If the localization context does not have any locale, the locale of the java.text.MessageFormat is set to the locale returned by the formatting locale lookup algorithm of Establishing a Formatting Locale, except that the available formatting locales are given as the intersection of the number- and date- formatting locales. If this algorithm does not yield any locale, the locale of the java.text.MessageFormat is set to the runtime’s default locale.

If the message is compound and no <fmt:param> subtags are specified, it is left unmodified (that is, java.text.MessageFormat is not used).

The <fmt:message> action outputs its result to the current JspWriter object, unless the var attribute is specified, in which case the result is stored in the named Jakarta Server Pages attribute.

8.9. <fmt:param>

Supplies a single parameter for parametric replacement to a containing <fmt:message> (see <fmt:message>) action.

Syntax

Syntax 1: value specified via attribute "value"

<fmt:param value="messageParameter"/>

Syntax 2: value specified via body content

<fmt:param>
    body content
</fmt:param>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dynamic Type Description

value

true

Object

Argument used for parametric replacement.

Constraints
  • Must be nested inside a <fmt:message> action.

Description

The <fmt:param> action supplies a single parameter for parametric replacement to the compound message given by its parent <fmt:message> action.

Parametric replacement takes place in the order of the <fmt:param> tags. The semantics of the replacement are defined as in the class java.text.MessageFormat:

the compound message given by the parent <fmt:message> action is used as the argument to the applyPattern() method of a java.text.MessageFormat instance, and the values of the <fmt:param> tags are collected in an Object[] and supplied to that instance’s format() method.

The argument value may be specified via the value attribute or inline via the tag’s body content.

8.10. <fmt:requestEncoding>

Sets the request’s character encoding.

Syntax
<fmt:requestEncoding [value="charsetName"]/>
Body Content

Empty.

Attributes
Name Dynamic Type Description

value

true

String

Name of character encoding to be applied when decoding request parameters.

Description

The <fmt:requestEncoding> action may be used to set the request’s character encoding, in order to be able to correctly decode request parameter values whose encoding is different from ISO-8859-1.

This action is needed because most browsers do not follow the HTTP specification and fail to include a Content-Type header in their requests.

More specifically, the purpose of the <fmt:requestEncoding> action is to set the request encoding to be the same as the encoding used for the response containing the form that invokes this page.

This action calls the setCharacterEncoding() method on the servlet request with the character encoding name specified in the value attribute. It must be used before any parameters are retrieved, either explicitly or through the use of an Expression Language expression.

If the character encoding of the request parameters is not known in advance (since the locale and thus character encoding of the page that generated the form collecting the parameter values was determined dynamically), the value attribute must not be specified. In this case, the <fmt:requestEncoding> action first checks if there is a charset defined in the request Content-Type header. If not, it uses the character encoding from the jakarta.servlet.jsp.jstl.fmt.request.charset scoped variable which is searched in session scope. If this scoped variable is not found, the default character encoding (ISO-8859-1) is used.

8.11. Configuration Settings

This section describes the i18n-related configuration settings. Refer to Configuration Data for more information on how the Jakarta Standard Tag Library processes configuration data.

8.11.1. Locale

Variable name

jakarta.servlet.jsp.jstl.fmt.locale

Java Constant

Config.FMT_LOCALE

Type

String or java.util.Locale

Set by

<fmt:setLocale>

Used by

<fmt:bundle>, <fmt:setBundle>, <fmt:message>, <fmt:formatNumber>, <fmt:parseNumber>, <fmt:formatDate>, <fmt:parseDate>

Specifies the locale to be used by the i18n-capable formatting actions, thereby disabling browser-based locales. A String value is interpreted as defined in action <fmt:setLocale> (see <fmt:setLocale>).

8.11.2. Fallback Locale

Variable name

jakarta.servlet.jsp.jstl.fmt.fallbackLocale

Java Constant

Config.FMT_FALLBACK_LOCALE

Type

String or java.util.Locale

Set by

Used by

<fmt:bundle>, <fmt:setBundle>, <fmt:message>, <fmt:formatNumber>, <fmt:parseNumber>, <fmt:formatDate>, <fmt:parseDate>

Specifies the fallback locale to be used by the i18n-capable formatting actions if none of the preferred match any of the available locales. A String value is interpreted as defined in action <fmt:setLocale> (see <fmt:setLocale>).

8.11.3. I18n Localization Context

Variable name

jakarta.servlet.jsp.jstl.fmt.localizationContext

Java Constant

Config.FMT_LOCALIZATION_CONTEXT

Type

String or jakarta.servlet.jsp.jstl.fmt.LocalizationContext

Set by

<fmt:setBundle>

Used by

<fmt:message>, <fmt:formatNumber>, <fmt:parseNumber>, <fmt:formatDate>, <fmt:parseDate>

Specifies the default i18n localization context to be used by the i18n-capable formatting actions. A String value is interpreted as a resource bundle basename.

9. Formatting Actions: I18n-capable formatting tag library

The Jakarta Standard Tag Library formatting actions allow various data elements in a Jakarta Server Pages page, such as numbers, dates and times, to be formatted and parsed in a locale-sensitive or customized manner.

9.1. Overview

9.1.1. Formatting Numbers, Currencies, and Percentages

The <fmt:formatNumber> action allows page authors to format numbers, currencies, and percentages according to the client’s cultural formatting conventions.

For example, the output of:

<fmt:formatNumber value="9876543.21" type="currency"/>

varies with the page’s locale (given in parentheses), as follows:

     SFr. 9'876'543.21 (fr_CH)
     $9,876,543.21 (en_US)

While the previous example uses the default formatting pattern (for currencies) of the page’s locale, it is also possible to specify a customized formatting pattern. For example, a pattern of ".000" will cause any numeric value formatted with it to be represented with 3 fraction digits, adding trailing zeros if necessary, so that:

<fmt:formatNumber value="12.3" pattern=".000"/>

will output "12.300".

Likewise, a pattern of '"#,#00.0#"' specifies that any numeric value formatted with it will be represented with a minimum of 2 integer digits, 1 fraction digit, and a maximum of 2 fraction digits, with every 3 integer digits grouped. Applied to "123456.7891", as in:

<fmt:formatNumber value="123456.7891" pattern="#,#00.0#"/>

the formatted output will be "123,456.79" (note that rounding is handled automatically).

The following example formats a numeric value as a currency, stores it in a scoped variable, parses it back in, and outputs the parsed result (which is the same as the original numeric value):

<fmt:formatNumber value="123456789" type="currency" var="cur"/>
<fmt:parseNumber value="${cur}" type="currency"/>

A similar sequence of actions could have been used to retrieve a currency-formatted value from a database, parse its numeric value, perform an arithmetic operation on it, reformat it as a currency, and store it back to the database.

9.1.2. Formatting Dates and Times

The <fmt:formatDate> action allows page authors to format dates and times according to the client’s cultural formatting conventions.

For example, assuming a current date of Oct 22, 2001 and a current time of 4:05:53PM, the following action:

<jsp:useBean id="now" class="java.util.Date"/>
<fmt:formatDate value="${now}" timeStyle="long" dateStyle="long"/>

will output

October 22, 2001 4:05:53 PM PDT

for the U.S. and

22 octobre 2001 16:05:53 GMT-07:0

for the French locale.

Page authors may also specify a customized formatting style for their dates and times. Assuming the same current date and time as in the above example, this action:

<fmt:formatDate value="${now}" pattern="dd.MM.yy"/>_

will output

22.10.01

for the U.S. locale.

Time information on a page may be tailored to the preferred time zone of a client. This is useful if the server hosting the page and its clients reside in different time zones. If time information is to be formatted or parsed in a time zone different from that of the Jakart Server Pages container, the <fmt:formatDate> and <fmt:parseDate> action may be nested inside a <fmt:timeZone> action or supplied with a timeZone attribute.

In the following example, the current date and time are formatted in the "GMT+1:00" time zone:

<fmt:timeZone value="GMT+1:00">
    <fmt:formatDate value="${now}" type="both" dateStyle="full"
        timeStyle="full"/>
</fmt:timeZone>

9.2. Formatting Locale

A formatting action[8] may leverage an i18n localization context to determine its formatting locale or establish a formatting locale on its own, by following these steps:

  • <fmt:bundle> action
    If a formatting action is nested inside a <fmt:bundle> action (see <fmt:bundle>), the locale of the i18n localization context of the enclosing <fmt:bundle> action is used as the formatting locale. The <fmt:bundle> action determines the resource bundle of its i18n localization context according to the resource bundle determination algorithm in Determinining the Resource Bundle for an i18n Localization Context, using the basename attribute as the resource bundle basename. If the i18n localization context of the enclosing <fmt:bundle> action does not contain any locale, go to the next step.

  • I18n default localization context
    The default i18n localization context may be specified via the jakarta.servlet.jsp.jstl.fmt.localizationContext configuration setting. If such a configuration setting exists, and its value is of type LocalizationContext, its locale is used as the formatting locale. Otherwise, if the configuration setting is of type String, the formatting action establishes its own i18n localization context and uses its locale as the formatting locale (in this case, the resource bundle component of the i18n localization context is determined according to the resource bundle determination algorithm in Determinining the Resource Bundle for an i18n Localization Context, using the configuration setting as the resource bundle basename). If the i18n localization context determined in this step does not contain any locale, go to the next step.

  • Formatting locale lookup
    The formatting action establishes a locale according to the algorithm described in Establishing a Formatting Locale. This algorithm requires the preferred locales. The way the preferred locales are set is exactly the same as with i18n actions and is described in Preferred Locales.

The following example shows how the various localization contexts can be established to define the formatting locale.

<jsp:useBean id="now" class="java.util.Date"/>

<%-- Formatting locale lookup --%>
<fmt:formatDate value="${now}" />

<fmt:bundle basename="Greetings">
    <%-- I18n localization context from parent <fmt:bundle> tag --%>
    <fmt:message key="Welcome" />
    <fmt:formatDate value="${now}" />
</fmt:bundle>

9.3. Establishing a Formatting Locale

If a formatting action fails to leverage an i18n localization context for its formatting locale – either because the formatting action has no way of referring to an i18n localization context, or the i18n localization context does not have any locale – it must establish the formatting locale on its own, given an ordered set of preferred locales, according to the formatting locale lookup algorithm described in this section.

9.3.1. Locales Available for Formatting Actions

The algorithm described in Formatting Locale Lookup Algorithm compares preferred locales against the set of locales that are available for a specific formatting action.

The locales available for actions <fmt:formatNumber> and <fmt:parseNumber> are determined by a call to java.text.NumberFormat.getAvailableLocales().

The locales available for <fmt:formatDate> and <fmt:parseDate> are determined by a call to java.text.DateFormat.getAvailableLocales().

9.3.2. Locale Lookup

The algorithm of Formatting Locale Lookup Algorithm describes how the proper locale is determined. This algorithm calls for a locale lookup: it attempts to find among the available locales, a locale that matches the specified one.

The locale lookup is similar to the resource bundle lookup described in Resource Bundle Lookup, except that instead of trying to match a resource bundle, the locale lookup tries to find a match in a list of available locales. A match of the specified locale against an available locale is therefore attempted in the following order:

  • Language, country, and variant are the same

  • Language and country are the same

  • Language is the same and the available locale does not have a country

9.3.3. Formatting Locale Lookup Algorithm

Notes:

  • When there are multiple preferred locales, they are processed in the order they were returned by a call to ServletRequest.getLocales().

  • The algorithm stops as soon as a locale has been selected for the localization context.

Step 1: Find a match within the ordered set of preferred locales

A locale lookup (see Locale Lookup) is performed for each one of the preferred locales until a match is found. The first match is used as the formatting locale.

Step 2: Find a match with the fallback locale

A locale lookup (see Locale Lookup) is performed for the fallback locale specified in the jakarta.servlet.jsp.jstl.fmt.fallbackLocale configuration setting. If a match exists, it is used as the formatting locale.

If no match is found after the above two steps, it is up to the formatting action to take a corrective action.

The result of the formatting locale lookup algorithm may be cached, so that subsequent formatting actions that need to establish the formatting locale on their own may leverage it.

9.4. Time Zone

Time information on a page may be tailored to the preferred time zone of a client. This is useful if the server hosting the page and its clients reside in different time zones (page authors could be advised to always use the "long" time format which includes the time zone, but that would still require clients to convert the formatted time into their own time zone).

When formatting time information using the <fmt:formatDate> action (see <fmt:formatDate>), or parsing time information that does not specify a time zone using the <fmt:parseDate> action (see <fmt:parseDate>), the time zone to use is determined as follows and in this order:

  • Use the time zone from the action’s timeZone attribute.

  • If attribute timeZone is not specified and the action is nested inside an <fmt:timeZone> action, use the time zone from the enclosing <fmt:timeZone> action.

  • Use the time zone given by the jakarta.servlet.jsp.jstl.fmt.timeZone configuration setting.

  • Use the Jakarta Server Pages container’s time zone.

9.5. <fmt:timeZone>

Specifies the time zone in which time information is to be formatted or parsed in its body content.

Syntax
<fmt:timeZone value="timeZone">
    body content
</fmt:timeZone>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content and then writes it to the current JspWriter. The action ignores the body content.

Attributes
Name Dyn Type Description

value

true

String or

java.util.TimeZone

The time zone. A String value is interpreted as a time zone ID. This may be one of the time zone IDs supported by the Java platform (such as "America/Los_Angeles") or a custom time zone ID (such as "GMT-8"). See java.util.TimeZone for more information on supported time zone formats.

Null & Error Handling
  • If value is null or empty, the GMT timezone is used.

Description

The <fmt:timeZone> action specifies the time zone in which to format or parse the time information of any nested time formatting (see <fmt:formatDate>) or parsing (see <fmt:parseDate>) actions.

If the time zone is given as a string, it is parsed using java.util.TimeZone.getTimeZone().

9.6. <fmt:setTimeZone>

Stores the specified time zone in a scoped variable or the time zone configuration variable.

Syntax
<fmt:setTimeZone value="timeZone"
                 [var="varName"]
                 [scope="{page|request|session|application}"]/>
Body Content

Empty.

Attributes
Name Dyn Type Description

value

true

String or

java.util.TimeZone

The time zone. A String value is interpreted as a time zone ID. This may be one of the time zone IDs supported by the Java platform (such as "America/Los_Angeles") or a custom time zone ID (such as "GMT-8"). See java.util.TimeZone for more information on supported time zone formats.

var

false

String

Name of the exported scoped variable which stores the time zone of type java.util.TimeZone.

scope

false

String

Scope of var or the time zone configuration variable.

Null & Error Handling
  • If value is null or empty, the GMT timezone is used.

Description

The <fmt:setTimeZone> action stores the given time zone in the scoped variable whose name is given by var. If var is not specified, the time zone is stored in the jakarta.servlet.jsp.jstl.fmt.timeZone configuration variable, thereby making it the new default time zone in the given scope.

If the time zone is given as a string, it is parsed using java.util.TimeZone.getTimeZone().

9.7. <fmt:formatNumber>

Formats a numeric value in a locale-sensitive or customized manner as a number, currency, or percentage.

Syntax

Syntax 1: without a body

<fmt:formatNumber value="numericValue"
                  [type="{number|currency|percent}"]
                  [pattern="customPattern"]
                  [currencyCode="currencyCode"]
                  [currencySymbol="currencySymbol"]
                  [groupingUsed="{true|false}"]
                  [maxIntegerDigits="maxIntegerDigits"]
                  [minIntegerDigits="minIntegerDigits"]
                  [maxFractionDigits="maxFractionDigits"]
                  [minFractionDigits="minFractionDigits"]
                  [var="varName"]
                  [scope="{page|request|session|application}"]/>

Syntax 2: with a body to specify the numeric value to be formatted

<fmt:formatNumber [type="{number|currency|percent}"]
                  [pattern="customPattern"]
                  [currencyCode="currencyCode"]
                  [currencySymbol="currencySymbol"]
                  [groupingUsed="{true|false}"]
                  [maxIntegerDigits="maxIntegerDigits"]
                  [minIntegerDigits="minIntegerDigits"]
                  [maxFractionDigits="maxFractionDigits"]
                  [minFractionDigits="minFractionDigits"]
                  [var="varName"]
                  [scope="{page|request|session|application}"]>
    numeric value to be formatted
</fmt:formatNumber>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

value

true

String or Number

Numeric value to be formatted.

type

true

String

Specifies whether the value is to be formatted as number, currency, or percentage.

pattern

true

String

Custom formatting pattern.

currencyCode

true

String

ISO 4217 currency code. Applied only when formatting currencies (i.e. if type is equal to "currency"); ignored otherwise.

currencySymbol

true

String

Currency symbol. Applied only when formatting currencies (i.e. if type is equal to "currency"); ignored otherwise.

groupingUsed

true

boolean

Specifies whether the formatted output will contain any grouping separators.

maxIntegerDigits

true

int

Maximum number of digits in the integer portion of the formatted output.

minIntegerDigits

true

int

Minimum number of digits in the integer portion of the formatted output.

maxFractionDigits

true

int

Maximum number of digits in the fractional portion of the formatted output.

minFractionDigits

true

int

Minimum number of digits in the fractional portion of the formatted output.

var

false

String

Name of the exported scoped variable which stores the formatted result as a String.

scope

false

String

Scope of var.

Constraints
  • If scope is specified, var must also be specified.

  • The value of the currencyCode attribute must be a valid ISO 4217 currency code.

Null & Error Handling
  • If value is null or empty, nothing is written to the current JspWriter object and the scoped variable is removed if it is specified (see attributes var and scope).

  • If this action fails to determine a formatting locale, it uses Number.toString() as the output format.

  • If the attribute pattern is null or empty, it is ignored.

  • If an exception occurs during the parsing of a string value, it must be caught and rethrown as a JspException. The message of the rethrown JspException must include the string value, and the caught exception must be provided as the root cause.

Description

The numeric value to be formatted may be specified via the value attribute; if missing, it is read from the tag’s body content.

The formatting pattern may be specified via the pattern attribute, or is looked up in a locale-dependent fashion.

A pattern string specified via the pattern attribute must follow the pattern syntax specified by the class java.text.DecimalFormat.

If looked up in a locale-dependent fashion, the formatting pattern is determined via a combination of the formatting locale, which is determined according to Formatting Locale, and the type attribute. Depending on the value of the type attribute, the given numeric value is formatted as a number, currency, or percentage. The locale’s default formatting pattern for numbers, currencies, or percentages is determined by calling the java.text.NumberFormat method getNumberInstance, getCurrencyInstance, or getPercentInstance, respectively, with the formatting locale.

The pattern attribute takes precedence over type. In either case, the formatting symbols (such as decimal separator and grouping separator) are given by the formatting locale.

The (specified or locale-dependent) formatting pattern may be further fine-tuned using the formatting options described below.

If the numeric value is given as a string literal, it is first parsed into a java.lang.Number. If the string does not contain any decimal point, it is parsed using java.lang.Long.valueOf(), or java.lang.Double.valueOf() otherwise.

The formatted result is output to the current JspWriter object, unless the var attribute is given, in which case it is stored in the named scoped variable.

Formatting Options

The groupingUsed attribute specifies whether the formatted ouput will contain any grouping separators. See the java.text.NumberFormat method setGroupingUsed() for more information.

The minimum and maximum number of digits in the integer and fractional portions of the formatted output may be given via the minIntegerDigits, maxIntegerDigits, minFractionDigits, and maxFractionDigits attributes, respectively. See the java.text.NumberFormat methods setMinimumIntegerDigits(), setMaximumIntegerDigits(), setMinimumFractionDigits(), and setMaximumFractionDigits() for more information.

Formatting Currencies

When formatting currencies using the specified or locale-dependent formatting pattern for currencies, the currency symbol of the formatting locale is used by default. It can be overridden by using the currencySymbol or currencyCode attributes, which specify the currency symbol or currency code, respectively, of the currency to use.

If both currencyCode and currencySymbol are present, currencyCode takes precedence over currencySymbol if the java.util.Currency class is defined in the container’s runtime (that is, if the container’s runtime is Java SE 1.4 or greater), and currencySymbol takes precendence otherwise. If only currencyCode is given, it is used as a currency symbol if java.util.Currency is not defined.

9.8. <fmt:parseNumber>

Parses the string representation of numbers, currencies, and percentages that were formatted in a locale-sensitive or customized manner.

Syntax

Syntax 1: without a body

<fmt:parseNumber value="numericValue"
                [type="{number|currency|percent}"]
                [pattern="customPattern"]
                [parseLocale="parseLocale"]
                [integerOnly="{true|false}"]
                [var="varName"]
                [scope="{page|request|session|application}"]/>

Syntax 2: with a body to specify the numeric value to be parsed

<fmt:parseNumber [type="{number|currency|percent}"]
                [pattern="customPattern"]
                [parseLocale="parseLocale"]
                [integerOnly="{true|false}"]
                [var="varName"]
                [scope="{page|request|session|application}"]>
    numeric value to be parsed
</fmt:parseNumber>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

value

true

String

String to be parsed.

type

true

String

Specifies whether the string in the value attribute should be parsed as a number, currency, or percentage.

pattern

true

String

Custom formatting pattern that determines how the string in the value attribute is to be parsed.

parseLocale

true

String or

java.util.Locale

Locale whose default formatting pattern (for numbers, currencies, or percentages, respectively) is to be used during the parse operation, or to which the pattern specified via the pattern attribute (if present) is applied.

integerOnly

true

boolean

Specifies whether just the integer portion of the given value should be parsed.

var

false

String

Name of the exported scoped variable which stores the parsed result (of type java.lang.Number).

scope

false

String

Scope of var.

Constraints
  • If scope is specified, var must also be specified.

Null & Error Handling
  • If the numeric string to be parsed is null or empty, the scoped variable defined by attributes var and scope is removed. This allows "empty" input to be distinguished from "invalid" input, which causes an exception.

  • If parseLocale is null or empty, it is treated as if it was missing.

  • If an exception occurs during the parsing of the value, it must be caught and rethrown as a JspException. The message of the rethrown JspException must include the value that was to be parsed, and the caught exception must be provided as the root cause.

  • If this action fails to determine a formatting locale, it must throw a JspException whose message must include the value that was to be parsed.

  • If the attribute pattern is null or empty, it is ignored.

Description

The numeric value to be parsed may be specified via the value attribute; if missing, it is read from the action’s body content.

The parse pattern may be specified via the pattern attribute, or is looked up in a locale-dependent fashion.

A pattern string specified via the pattern attribute must follow the pattern syntax specified by java.text.DecimalFormat.

If looked up in a locale-dependent fashion, the parse pattern is determined via a combination of the type and parseLocale attributes. Depending on the value of the type attribute, the given numeric value is parsed as a number, currency, or percentage. The parse pattern for numbers, currencies, or percentages is determined by calling the java.text.NumberFormat method getNumberInstance, getCurrencyInstance, or getPercentInstance, respectively, with the locale specified via parseLocale. If parseLocale is missing, the formatting locale, which is obtained according to Formatting Locale, is used as the parse locale.

The pattern attribute takes precedence over type. In either case, the formatting symbols in the pattern (such as decimal separator and grouping separator) are given by the parse locale.

The integerOnly attribute specifies whether just the integer portion of the given value should be parsed. See the java.text.NumberFormat method setParseIntegerOnly() for more information.

If the var attribute is given, the parse result (of type java.lang.Number) is stored in the named scoped variable. Otherwise, it is output to the current JspWriter object using java.lang.Number.toString().

9.9. <fmt:formatDate>

Allows the formatting of dates and times in a locale-sensitive or customized manner.

Syntax
<fmt:formatDate value="date"
                [type="{time|date|both}"]
                [dateStyle="{default|short|medium|long|full}"]
                [timeStyle="{default|short|medium|long|full}"]
                [pattern="customPattern"]
                [timeZone="timeZone"]
                [var="varName"]
                [scope="{page|request|session|application}"]/>
Body Content

Empty.

Attributes
Name Dynamic Type Description

value

true

java.util.

Date

Date and/or time to be formatted.

type

true

String

Specifies whether the time, the date, or both the time and date components of the given date are to be formatted.

dateStyle

true

String

Predefined formatting style for dates. Follows the semantics defined in class java.text.DateFormat. Applied only when formatting a date or both a date and time (i.e. if type is missing or is equal to "date" or "both"); ignored otherwise.

timeStyle

true

String

Predefined formatting style for times. Follows the semantics defined in class java.text.DateFormat. Applied only when formatting a time or both a date and time (i.e. if type is equal to "time" or "both"); ignored otherwise.

pattern

true

String

Custom formatting style for dates and times.

timeZone

true

String or java.util.

TimeZone

Time zone in which to represent the formatted time.

var

false

String

Name of the exported scoped variable which stores the formatted result as a String.

scope

false

String

Scope of var.

Constraints
  • If scope is specified, var must also be specified.

Null & Error Handling
  • If value is null or empty, nothing is written to the current JspWriter object and the scoped variable is removed if it is specified (see attributes var and scope).

  • If timeZone is null or empty, it is handled as if it was missing.

  • If this action fails to determine a formatting locale, it uses java.util.Date.toString() as the output format.

Description

Depending on the value of the type attribute, only the time, the date, or both the time and date components of the date specified via the value attribute or the body content are formatted, using one of the predefined formatting styles for dates (specified via the dateStyle attribute) and times (specified via the timeStyle attribute) of the formatting locale, which is determined according to Formatting Locale.

dateStyle and timeStyle support the semantics defined in java.text.DateFormat.

Page authors may also apply a customized formatting style to their times and dates by specifying the pattern attribute, in which case the type, dateStyle, and timeStyle attributes are ignored. The specified formatting pattern must use the pattern syntax specified by java.text.SimpleDateFormat.

In order to format the current date and time, a <jsp:useBean> action may be used as follows:

<jsp:useBean id="now" class="java.util.Date"/>
<fmt:formatDate value="${now}" />

If the string representation of a date or time needs to be formatted, the string must first be parsed into a java.util.Date using the <fmt:parseDate> action, whose parsing result may then be supplied to the <fmt:formatDate> action:

<fmt:parseDate value="4/13/02" pattern="M/d/yy" var="parsed"/>
<fmt:formatDate value="${parsed}" dateStyle="full"/>

The action’s result is output to the current JspWriter object, unless the var attribute is specified, in which case it is stored in the named scoped variable.

9.10. <fmt:parseDate>

Parses the string representation of dates and times that were formatted in a locale-sensitive or customized manner.

Syntax

Syntax 1: without a body

<fmt:parseDate value="dateString"
            [type="{time|date|both}"]
            [dateStyle="{default|short|medium|long|full}"]
            [timeStyle="{default|short|medium|long|full}"]
            [pattern="customPattern"]
            [timeZone="timeZone"]
            [parseLocale="parseLocale"]
            [var="varName"]
            [scope="{page|request|session|application}"]/>

Syntax 2: with a body to specify the date value to be parsed

<fmt:parseDate [type="{time|date|both}"]
            [dateStyle="{default|short|medium|long|full}"]
            [timeStyle="{default|short|medium|long|full}"]
            [pattern="customPattern"]
            [timeZone="timeZone"]
            [parseLocale="parseLocale"]
            [var="varName"]
            [scope="{page|request|session|application}"]>
    date value to be parsed
</fmt:parseDate>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

value

true

String

Date string to be parsed.

type

true

String

Specifies whether the date string in the value attribute is supposed to contain a time, a date, or both.

dateStyle

true

String

Predefined formatting style for days which determines how the date component of the date string is to be parsed. Applied only when formatting a date or both a date and time (i.e. if type is missing or is equal to "date" or "both"); ignored otherwise.

timeStyle

true

String

Predefined formatting styles for times which determines how the time component in the date string is to be parsed. Applied only when formatting a time or both a date and time (i.e. if type is equal to "time" or "both"); ignored otherwise.

pattern

true

String

Custom formatting pattern which determines how the date string is to be parsed.

timeZone

true

String or java.util.TimeZone

Time zone in which to interpret any time information in the date string.

parseLocale

true

String or

java.util.Locale

Locale whose predefined formatting styles for dates and times are to be used during the parse operation, or to which the pattern specified via the pattern attribute (if present) is applied.

var

false

String

Name of the exported scoped variable in which the parsing result (of type java.util.Date) is stored.

scope

false

String

Scope of var.

Constraints
  • If scope is specified, var must also be specified.

Null & Error Handling
  • If the date string to be parsed is null or empty, the scoped variable defined by var and scope is removed. This allows "empty" input to be distinguished from "invalid" input, which causes an exception.

  • If timeZone is null or empty, it is treated as if it was missing.

  • If parseLocale is null or empty, it is treated as if it was missing.

  • If an exception occurs during the parsing of the value, it must be caught and rethrown as a JspException. The message of the rethrown JspException must include the value that was to be parsed, and the caught exception must be provided as the root cause.

  • If this action fails to determine a formatting locale, it must throw a JspException whose message must include the value that was to be parsed.

Description

The date string to be parsed may be specified via the value attribute or via the tag’s body content.

Depending on the value of the type attribute, the given date string is supposed to contain only a time, only a date, or both. It is parsed according to one of the predefined formatting styles for dates (specified via the dateStyle attribute) and times (specified via the timeStyle attribute) of the locale specified by the parseLocale attribute. If the parseLocale attribute is missing, the formatting locale, which is determined according to Formatting Locale, is used as the parse locale.

If the given date string uses a different format, the pattern required to parse it must be specified via the pattern attribute, which must use the pattern syntax specified by java.text.SimpleDateFormat. In this case, the type, dateStyle, and timeStyle attributes are ignored. Parsing is non-lenient, i.e. the given date string must strictly adhere to the parsing format.

If the given time information does not specify a time zone, it is interpreted in the time zone determined according to Section Time Zone.

If the var attribute is given, the parsing result (of type java.util.Date ) is stored in the named scoped variable. Otherwise, it is output to the current JspWriter using the java.util.Date method toString().

9.11. Configuration Settings

This section describes the formatting-related configuration settings. Refer to Configuration Data for more information on how the Jakarta Standard Tag Library processes configuration data.

9.11.1. TimeZone

Variable name

jakarta.servlet.jsp.jstl.fmt.timeZone

Java Constant

Config.FMT_TIMEZONE

Type

String or java.util.TimeZone

Set by

<fmt:setTimeZone>

Used by

<fmt:formatDate>, <fmt:parseDate>

Specifies the application’s default time zone. A String value is interpreted as defined in action <fmt:timeZone> (see <fmt:timeZone>).

10. SQL Actions: sql tag library

Many web applications need to access relational databases as the source of dynamic data for their presentation layer. While it is generally preferred to have database operations handled within the business logic of a web application designed with an MVC architecture, there are situations where page authors require this capability within their Jakarta Server Pages (e.g. prototyping/testing, small scale/simple applications, lack of developer resources).

The Jakarta Standard Tag Library SQL actions provide the basic capabilities to easily interact with relational databases.

10.1. Overview

The Jakarta Standard Tag Library SQL actions allow page authors to:

  • Perform database queries (select)

  • Easily access query results

  • Perform database updates (insert, update, delete)

  • Group several database operations into a transaction

10.1.1. Data Source

SQL actions operate on a data source, as defined by the Java class javax.sql.DataSource. A DataSource object provides connections to the physical data source it represents. Within the context of a Connection retrieved from the DataSource, SQL statements are executed and results are returned.

A data source can be specified explicitly via the dataSource attribute in SQL actions, or it can be totally transparent to a page author by taking advantage of the data source configuration setting (jakarta.servlet.jsp.jstl.sql.dataSource).

There are two ways a data source can be specified as a string.

The first way is through a JNDI relative path, assuming a container supporting JNDI. For example, with the absolute JNDI resource path java:comp/env/jdbc/myDatabase, the JNDI relative path to the data source resource would simply be jdbc/myDatabase, given that java:comp/env is the standard JNDI root for a J2EE application.

The second way is by specifying the parameters needed by the JDBC DriverManager class, using the following syntax (see <sql:setDataSource> for details on the JDBC parameters)

     url[,[driver][,[user][,password]]]

For example,

     jdbc:mysql://localhost/,org.gjt.mm.mysql.Driver

where the database has been setup for access without any username or password. If the ',' character occurs in any of the JDBC parameters, it can be escaped by '\'. The character '\' itself can be escaped in the same way.

While the JDBC DriverManager class provides a low cost way to use SQL actions, it is not recommended to use it other than for prototyping purposes because it does not provide connection management features one can expect from a properly designed DataSource object.

10.1.2. Querying a Database

The most common use of the database actions is to query a database and display the results of the query.

The following sample code selects all customers from China from the customers table in the database, orders them by last name, and finally displays their last name, first name, and address in an HTML table.

<sql:query var="customers" dataSource="${dataSource}">
    SELECT * FROM customers
    WHERE country = 'China'
    ORDER BY lastname
</sql:query>

<table>
    <c:forEach var="row" items="${customers.rows}">
        <tr>
            <td><c:out value="${row.lastName}"/></td>
            <td><c:out value="${row.firstName}"/></td>
            <td><c:out value="${row.address}"/></td>
        </tr>
    </c:forEach>
</table>

This next example shows a generic way to display the results of a query with column names as headers:

<table>
    <!-- column headers -->
    <tr>
        <c:forEach var="columnName" items="${result.columnNames}">
            <th><c:out value="${columnName}"/></th>
        </c:forEach>
    </tr>
    <!-- column data -->
    <c:forEach var="row" items="${result.rowsByIndex}">
        <tr>
            <c:forEach var="column" items="${row}">
                <td><c:out value="${column}"/></td>
            </c:forEach>
        </tr>
    </c:forEach>
</table>

10.1.3. Updating a Database

The <sql:update> action updates a database. To ensure database integrity, several updates to a database may be grouped into a transaction by nesting the <sql:update> actions inside a <sql:transaction> action.

For example, the following code transfers money between two accounts in one transaction:

<sql:transaction dataSource="${dataSource}">
    <sql:update>
        UPDATE account
        SET Balance = Balance - ?
        WHERE accountNo = ?
        <sql:param value="${transferAmount}"/>
        <sql:param value="${accountFrom}"/>
    </sql:update>
    <sql:update>
        UPDATE account
        SET Balance = Balance + ?
        WHERE accountNo = ?
        <sql:param value="${transferAmount}"/>
        <sql:param value="${accountTo}"/>
    </sql:update>
</sql:transaction>

10.1.4. SQL Statement Parameters

The Jakarta Standard Tag Library database actions support substituting parameter values for parameter markers ("?") in SQL statements (as shown in the previous example). This form of parametric replacement is exposed by the jakarta.servlet.jsp.jstl.sql.SQLExecutionTag interface.

The SQLExecutionTag interface is implemented by the tag handlers for <sql:query> and <sql:update>. It is exposed in order to support custom parameter actions. These custom actions may retrieve their parameters from any source and process them before substituting them for a parameter marker in the SQL statement of the enclosing SQLExecutionTag action.

For example, a GUI front end may have a user enter a date as three separate fields (year, month, and day), and use this information in a database query. If the database table being accessed provides only a single column for the complete date, action <acme:dateParam> could assemble the three separate input parameters into one and pass it to the addSQLParameter() method of its enclosing SQLExecutionTag action:

<sql:update>
    UPDATE PersonalInfo
    SET BirthDate = ?
    WHERE clientId = ?
    <acme:dateParam year="${year}" month="${month}" day="${day}"/>
    <sql:param value="${clientId}"/>
</sql:update>

The Jakarta Standard Tag Library formatting tags may be used to parse the string representation of dates and numbers into instances of java.util.Date and java.lang.Number, respectively, before supplying them to an enclosing SQLExecutionTag for parametric replacement:

<sql:update sql="${sqlUpdateStmt}" dataSource="${dataSource}">
    <fmt:parseDate var="myDate" value="${someDate}"/>
    <sql:param value="${myDate}"/>
</sql:update>

10.2. Database Access

This section describes the algorithm used by the SQL actions (<sql:query>, <sql:update>, <sql:transaction>) to access a database.

  • Try to get a reference to a data source as follows:

    • If the attribute dataSource is specified, use the value specified for that attribute as the data source.

    • Otherwise, get the configuration setting associated with jakarta.servlet.jsp.jstl.sql.dataSource using Config.find() (see Configuration Data). Use the value found as the data source if it is not null.

  • If a data source is obtained from the previous step:

    • If it is a DataSource object, this is the data source used by the action to access the database.

    • Otherwise, if it is a String:

      • Assume this is a JNDI relative path and retrieve the data source from the container’s JNDI naming context by concatenating the specified relative path to the J2EE defined root (java:comp/env/).

      • If the previous step fails (data source not found), assume the string specifies JDBC parameters using the syntax described in Data Source and do as follows:

      • If driver is specified, ensure it is loaded

      • Access the named URL through the DriverManager class, using an empty string for user or password if they are not specified.

    • If the previous step fails, throw an exception.

  • Otherwise, throw an exception.

An implementation need not create new objects each time a SQL action is called and the algorithm above does not yield a DataSource object directly; i.e when a JNDI path or parameters for the JDBC DriverManager class are used. It may reuse objects that it previously created for identical arguments.

It is important to note that actions that open a connection to a database must close the connection as well as release any other associated resources (for example, Statement, PreparedStatement and ResultSet objects) by the time the action completes. This ensures that no connections are left open and that leaks are avoided when these actions are used with pooling mechanisms.

10.3. <sql:query>

Queries a database.

Syntax

Syntax 1: Without body content

<sql:query sql="sqlQuery"
        var="varName" [scope="{page|request|session|application}"]
        [dataSource="dataSource"]
        [maxRows="maxRows"]
        [startRow="startRow"]/>

Syntax 2: With a body to specify query arguments

<sql:query sql="sqlQuery"
        var="varName" [scope="{page|request|session|application}"]
        [dataSource="dataSource"]
        [maxRows="maxRows"]
        [startRow="startRow"]>
    <sql:param> actions
</sql:query>

Syntax 3: With a body to specify query and optional query parameters

<sql:query var="varName"
        [scope="{page|request|session|application}"]
        [dataSource="dataSource"]
        [maxRows="maxRows"]
        [startRow="startRow"]>
    query
    optional <sql:param> actions
</sql:query>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dynamic Type Description

sql

true

String

SQL query statement.

dataSource

true

javax.sql.DataSource or String

Data source associated with the database to query. A String value represents a relative path to a JNDI resource or the parameters for the DriverManager class.

maxRows

true

int

The maximum number of rows to be included in the query result. If not specified, or set to -1, no limit on the maximum number of rows is enforced.

startRow

true

int

The returned Result object includes the rows starting at the specified index. The first row of the original query result set is at index 0. If not specified, rows are included starting from the first row at index 0.

var

false

String

Name of the exported scoped variable for the query result. The type of the scoped variable is

jakarta.servlet.jsp.jstl.sql.Result.

scope

false

String

Scope of var.

Constraints
  • If dataSource is specified, this action must not be nested inside a <sql:transaction>.[9]

  • maxRows must be >= -1

Null & Error Handling
  • If dataSource is null, a JspException is thrown.

  • If an exception occurs during the execution of this action, it must be caught and rethrown as a JspException. The message of the rethrown JspException must include the SQL statement, and the caught exception must be provided as the root cause.

Description

The <sql:query> action queries a database and returns a single result set containing rows of data that it stores in the scoped variable identified by the var and scope attributes.

If the query produces no results, an empty Result object (of size zero) is returned.

The SQL query statement may be specified by the sql attribute or from the action’s body content.

The query statement may contain parameter markers ("?") identifying JDBC PreparedStatement parameters, whose values must be supplied by nested parameter actions (such as <sql:param>). The <sql:query> action implements the jakarta.servlet.jsp.jstl.sql.SQLExecutionTag interface, allowing parameter values to be supplied by custom parameter actions.

maxRows and startRow

The maximum number of rows to be included in the query result may be specified by the maxRows attribute (for a specific <sql:query> action) or by the configuration setting jakarta.servlet.jsp.jstl.sql.maxRows (see Configuration Data and Configuration Settings). Attribute maxRows has priority over the configuration setting. A value of -1 means that no limit is enforced on the maximum number of rows.

The startRow attribute may be used to specify the index of the first row to be included in the returned Result object. For example, if given a value of 10, the returned Result object will start with the row located at index 10 (i.e. rows 0 through 9 of the original query result set are skipped). All remaining rows of the original query result set are included.

If both startRow and maxRows are specified, a maximum of startRow + maxRows rows are retrieved from the database. All rows up to startRow are then discarded, and the remaining rows (from startRow through startRow + maxRows) are included in the result.

When using startRow, it is important to note that the order in which rows are returned is not guaranteed between RDBMS implementations unless an "order by" clause is specified in the query.

maxRows and startRow protect against so-called "runaway queries", allow efficient access to the top rows of large result sets, and also provide a "poor-man’s way" of paging through a large query result by increasing startRow by maxRows over a previous page.

Obtaining and Releasing a Connection

If <sql:query> is nested inside an <sql:transaction> action, the Connection object is obtained from that parent <sql:transaction> which is reponsible for managing access to the database.

Otherwise, access to the database is performed according to the algorithm described in Database Access. A Connection object is obtained and released before the action completes.

10.4. <sql:update>

Executes an SQL INSERT, UPDATE, or DELETE statement. In addition, SQL statements that return nothing, such as SQL DDL statements, can be executed.

Syntax

Syntax 1: Without body content

<sql:update sql="sqlUpdate"
        [dataSource="dataSource"]
        [var="varName"]
        [scope="{page|request|session|application}"]/>

Syntax 2: With a body to specify update parameters

<sql:update sql="sqlUpdate"
        [dataSource="dataSource"]
        [var="varName"]
        [scope="{page|request|session|application}"]>
    <sql:param> actions
</sql:update>

Syntax 3: With a body to specify update statement and optional update parameters

<sql:update [dataSource="dataSource"]
        [var="varName"] [scope="{page|request|session|application}"]>
    update statement
    optional <sql:param> actions
</sql:update>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

sql

true

String

SQL update statement.

dataSource

true

javax.sql.

DataSource or String

Data source associated with the database to update. A String value represents a relative path to a JNDI resource or the parameters for the JDBC DriverManager class.

var

false

String

Name of the exported scoped variable for the result of the database update. The type of the scoped variable is java.lang.Integer.

scope

false

String

Scope of var.

Constraints
  • If scope is specified, var must also be specified.

  • If dataSource is specified, this action must not be nested inside a <sql:transaction>.

Null & Error Handling
  • If dataSource is null, a JspException is thrown.

  • If an exception occurs during the execution of this action, it must be caught and rethrown as a JspException. The message of the rethrown JspException must include the SQL statement, and the caught exception must be provided as the root cause.

Description

The SQL update statement may be specified by the sql attribute or from the action’s body content.

The update statement may contain parameter markers ("?") identifying JDBC PreparedStatement parameters, whose values must be supplied by nested parameter actions (such as <sql:param>). The <sql:update> action implements the jakarta.servlet.jsp.jstl.sql.SQLExecutionTag interface, allowing the parameter values to be supplied by custom parameter tags.

The connection to the database is obtained in the same manner as described for <sql:query>.

The result of an <sql:update> action is stored in a scoped variable named by the var attribute, if that attribute was specified. That result represents the number of rows that were affected by the update. Zero is returned if no rows were affected by INSERT, DELETE, or UPDATE, and for any SQL statement that returns nothing (such as SQL DDL statements). This is consistent with method executeUpdate() of the JDBC class Statement.

10.5. <sql:transaction>

Establishes a transaction context for <sql:query> and <sql:update> subtags.

Syntax
<sql:transaction [dataSource="dataSource"]
        [isolation=isolationLevel]>
    <sql:query> and <sql:update> statements
</sql:transaction>

isolationLevel ::= "read_committed"
                | "read_uncommitted"
                | "repeatable_read"
                | "serializable"
Body Content

Jakarta Server Pages content. The Jakart Server Pages container processes the body content and then writes the result to the current JspWriter. The action ignores the body content.

Attributes
Name Dyn Type Description

dataSource

true

javax.sql.

DataSource

or String

DataSource associated with the database to access. A String value represents a relative path to a JNDI resource or the parameters for the JDBC DriverManager facility.

isolation

true

String

Transaction isolation level. If not specified, it is the isolation level the DataSource has been configured with.

Constraints
  • Any nested <sql:query> and <sql:update> actions must not specify a dataSource attribute.

Null & Error Handling
  • If dataSource is null, a JspException is thrown.

  • Any exception occurring during the execution of this action must be caught and rethrown after the transaction has been rolled back (see description below for details).

Description

The <sql:transaction> action groups nested <sql:query> and <sql:update> actions into a transaction.

The transaction isolation levels are defined by java.sql.Connection.

The tag handler of the <sql:transaction> action must perform the following steps in its lifecycle methods:

  • doStartTag():

    • Determines the transaction isolation level the DBMS is set to (using the Connection method getTransactionIsolation()).
      If transactions are not supported (that is, the transaction isolation level is equal to TRANSACTION_NONE), an exception is raised, causing the transaction to fail.
      For any other transaction isolation level, the auto-commit mode is is saved (so it can later be restored), and then disabled by calling setAutoCommit(false) on the Connection.

    • If the isolation attribute is specified and differs from the connection’s current isolation level, the current transaction isolation level is saved (so it can later be restored) and set to the specified level (using the Connection method setTransactionIsolation()).

  • doEndTag(): Calls the Connection method commit().

  • doCatch(): Calls the Connection method rollback().

  • doFinally():

    • If a transaction isolation level has been saved, it is restored using the Connection method setTransactionIsolation().

    • Restore auto-commit mode to its saved value by calling setAutoCommit() on the Connection.

    • Closes the connection.

The Connection object is obtained and managed in the same manner as described for <sql:query> (see <sql:query>), except that it is never obtained from a parent tag (<sql:transaction> tags can not be nested as a means to propagate a Connection).

Note that the <sql:transaction> tag handler commits or rollbacks the transaction (if it catches an exception) by calling the JDBC Connection commit() and rollback() methods respectively. Executing the corresponding SQL statements using <sql:update>, e.g. <sql:update sql="rollback" />, within the <sql:transaction> element body is not supported and the result of doing so is unpredictable.

Finally, the behavior of the <sql:transaction> action is undefined if it executes in the context of a larger JTA user transaction.

10.6. <sql:setDataSource>

Exports a data source either as a scoped variable or as the data source configuration variable (jakarta.servlet.jsp.jstl.sql.dataSource).

Syntax
<sql:setDataSource
        {dataSource="dataSource" |
            url="jdbcUrl"
            [driver="driverClassName"]
            [user="userName"]
            [password="password"]}
        [var="varName"]
        [scope="{page|request|session|application}"]/>
Body Content

Empty.

Attributes
Name Dyn Type Description

dataSource

true

String or javax.sql.DataSource

Data source. If specified as a string, it can either be a relative path to a JNDI resource, or a JDBC parameters string as defined in Data Source.

driver

true

String

JDBC parameter: driver class name.

url

true

String

JDBC parameter: URL associated with the database.

user

true

String

JDBC parameter: database user on whose behalf the connection to the database is being made.

password

true

String

JDBC parameter: user password

var

false

String

Name of the exported scoped variable for the data source specified. Type can be String or DataSource.

scope

false

String

If var is specified, scope of the exported variable. Otherwise, scope of the data source configuration variable.

Null & Error Handling
  • If dataSource is null, a JspException is thrown.

Description

If the var attribute is specified, the <sql:setDataSource> action exports the data source specified (either as a DataSource object or as a String) as a scoped variable. Otherwise, the data source is exported in the jakarta.servlet.jsp.jstl.sql.dataSource configuration variable.

The data source may be specified either via the dataSource attribute (as a DataSource object, JNDI relative path, or JDBC parameters string), or via the four JDBC parameters attributes. These four attributes are provided as a simpler alternative to the JDBC parameters string syntax defined in Data Source that would have to be used with the dataSource attribute.

As mentioned in Data Source, using JDBC’s DriverManager class to access a database is intended for prototyping purposes only because it does not provide connection management features one can expect from a properly designed DataSource object.

10.7. <sql:param>

Sets the values of parameter markers ("?") in a SQL statement. Subtag of SQLExecutionTag actions such as <sql:query> and <sql:update>.

Syntax

Syntax 1: Parameter value specified in attribute "value"

<sql:param value="value"/>

Syntax 2: Parameter value specified in the body content

<sql:param>
    parameter value
</sql:param>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

value

true

Object

Parameter value.

Constraints
  • Must be nested inside an action whose tag handler is an instance of jakarta.servlet.jsp.jstl.sql.SQLExecutionTag.

Null & Error Handling
  • If value is null, the parameter is set to the SQL value NULL.

Description

The <sql:param> action substitutes the given parameter value for a parameter marker("?") in the SQL statement of its enclosing SQLExecutionTag action.

Parameters are substituted in the order in which they are specified.

The <sql:param> action locates its nearest ancestor that is an instance of SQLExecutionTag and calls its addSQLParameter() method, supplying it with the given parameter value.

It is important to note that the semantics of SQLExecutionTag.addSQLParameter() are such that supplying a parameter with a String value (e.g. when using syntax 2) only works for columns of text type (CHAR, VARCHAR or LONGVARCHAR).

10.8. <sql:dateParam>

Sets the values of parameter markers ("?") in a SQL statement for values of type java.util.Date. Subtag of SQLExecutionTag actions, such as <sql:query> and <sql:update>.

Syntax
<sql:dateParam value="value" [type="{timestamp|time|date}"]/>
Body Content

Empty.

Attributes
Name Dyn Type Description

value

true

java.util.Date

Parameter value for DATE, TIME, or TIMESTAMP column in a database table.

type

true

String

One of "date", "time" or "timestamp".

Constraints
  • Must be nested inside an action whose tag handler is an instance of jakarta.servlet.jsp.jstl.sql.SQLExecutionTag.

Null & Error Handling
  • If value is null, the parameter is set to the SQL value NULL.

Description

This action converts the provided java.util.Date instance to one of java.sql.Date, java.sql.Time or java.sql.Timestamp as defined by the type attribute as follows:

  • If the java.util.Date object provided by the value attribute is an instance of java.sql.Time, java.sql.Date, or java.sql.Timestamp, and the type attribute matches this object’s type, then it is passed as is to the database.

  • Otherwise, the object is converted to the appropriate type by calling that type’s constructor with a parameter of date.getTime(), where date is the value of the value attribute.

The <sql:dateParam> action substitutes the given parameter value for a parameter marker("?") in the SQL statement of its enclosing SQLExecutionTag action.

Parameters are substituted in the order in which they are specified.

The <sql:dateParam> action locates its nearest ancestor that is an instance of SQLExecutionTag and calls its addSQLParameter() method, supplying it with the given parameter value.

10.9. Configuration Settings

This section describes the configuration settings used by the SQL actions. Refer to Configuration Data for more information on how the Jakarta Standard Tag Library processes configuration data.

10.9.1. DataSource

Variable name

jakarta.servlet.jsp.jstl.sql.dataSource

Java Constant

Config.SQL_DATA_SOURCE

Type

String or javax.sql.DataSource

Set by

<sql:setDataSource>, Deployment Descriptor, Config class

Used by

<sql:query>, <sql:update>, <sql:transaction>

The data source to be accessed by the SQL actions. It can be specified as a string representing either a JNDI relative path or a JDBC parameters string (as defined in Data Source), or as a javax.sql.DataSource object.

10.9.2. MaxRows

Variable name

jakarta.servlet.jsp.jstl.sql.maxRows

Java Constant

Config.SQL_MAX_ROWS

Type

Integer

Set by

Deployment Descriptor, Config class

Used by

<sql:query>

The maximum number of rows to be included in a query result. If the maximum number of rows is not specified, or is -1, it means that no limit is enforced on the maximum number of rows. Value must be >= -1.

11. XML Core Actions: xml tag library

Enterprise data used in the web tier is increasingly XML these days — when companies cooperate over the web, XML is the data format of choice for exchanging information.

XML is therefore becoming more and more important in a page author’s life. The set of XML actions specified in the Jakarta Standard Tag Library is meant to address the basic XML needs a page author is likely to encounter.

The XML actions are divided in three categories: XML core actions (this chapter), XML flow control actions (XML Flow Control Actions: xml tag library), and XML transform actions (XML Transform Actions: xml tag library).

11.1. Overview

A key aspect of dealing with XML documents is to be able to easily access their content. XPath, a W3C recommendation since 1999, provides a concise notation for specifying and selecting parts of an XML document. The XML set of actions in the Jakarta Standard Tag Library is therefore based on XPath.

The introduction of XPath for the XML tagset expands the notion of expression language. XPath is an expression language that is used locally for the XML actions. Below are the rules of integration that XPath follows as a local expression language. These rules ensure that XPath integrates nicely within the Jakarta Standard Tag Library environment.

11.1.1. XPath Context

In XPath, the context for evaluating an expression consists of:

  • A node or nodeset

  • Variable bindings (see below)

  • Function library
    The default function library comes with the XPath engine. Some engines provide extension functions or allow customization to add new functions. The XPath function library in the Jakarta Standard Tag Library is limited to the core function library of the XPath specification.

  • Namespace prefix definitions which allow namespace prefixes to be used within an XPath expression.

11.1.2. XPath Variable Bindings

The XPath engine supports the following scopes to easily access web application data within an XPath expression. These scopes are defined in exactly the same way as their implicit object counterparts in the Jakarta Standard Tag Library expression language (see Section 2.4 Implicit Objects in the Jakarta Server Pages specification).

Expression Mapping

$foo

pageContext.findAttribute("foo")

$param:foo

request.getParameter("foo")

$header:foo

request.getHeader("foo")

$cookie:foo

maps to the cookie’s value for name foo

$initParam:foo

application.getInitParameter("foo")

$pageScope:foo

pageContext.getAttribute(
     "foo", PageContext.PAGE_SCOPE)

$requestScope:foo

pageContext.getAttribute(
     "foo", PageContext.REQUEST_SCOPE)

$sessionScope:foo

pageContext.getAttribute(
     "foo", PageContext.SESSION_SCOPE)

$applicationScope:foo

pageContext.getAttribute(
     "foo", PageContext.APPLICATION_SCOPE)

Through these mappings, Jakarta Server Pages scoped variables, request parameters, headers, and cookies, as well as context init parameters can all be used inside XPath expressions easily. For example:

/foo/bar[@x=$param:name]

would find the "bar" element with an attribute "x" equal to the value of the http request parameter "name".

11.1.3. Java to XPath Type Mappings

An XPath variable must reference a java.lang.Object instance in one of the supported scopes, identified by namespace prefix. The following mappings must be supported:

Java Type XPath Type

java.lang.Boolean

boolean

java.lang.Number

number

java.lang.String

string

Object exported by <x:parse>

node-set

A compliant implementation must allow an XPath variable to address objects exposed by that implementation’s handlers for <x:set> and <x:forEach>. For example, while an implementation of <x:set> may expose, for a node-set S, an object of any valid Java type, subsequent XPath evaluations must interpret this object as the node-set S.

An XPath expression must also treat variables that resolve to implementations of standard DOM interfaces as representing nodes of the type bound to that interface by the DOM specification.

XPath variable references that address objects of other types result in implementation-defined behavior. (An implementation may throw an exception if it encounters an unrecognized type.) Following the XPath specification (section 3.1), a variable name that is not bound to any value results in an exception.

11.1.4. XPath to Java Type Mappings

Evaluation of XPath expressions evaluate to XPath types. Their mapping to Java objects is defined as follows:

XPath Type Java Type
_boolean_

true or false

java.lang.Boolean

_number_

a floating-point number

java.lang.Number

_string_

a sequence of UCS characters

java.lang.String

_node-set_

an unordered collection of nodes without duplicates

Type usable by Jakarta Standard Tag Library XML-manipulation tags in the same Jakarta Standard Tag Library implementation. The specific Java type representing node-sets may thus vary by implementation.

11.1.5. The select Attribute

In all the XML actions of the Jakarta Standard Tag Library, XPath expressions are always specified using the select attribute. select is therefore always specified as a string literal that is evaluated by the XPath engine.

This clear separation, where only the select attribute of XML actions evaluates XPath expressions, helps avoid confusion between XPath (expression language that is local to the XML actions) and the Jakarta Standard Tag Library expression language (global to all actions with dynamic attributes in the Expression Language version of the tag library).

11.1.6. Default Context Node

The context node for every XPath expression evaluation in the Jakarta Standard Tag Library that does not appear in the body of an <x:forEach> tag is the root of an empty document. Page authors wishing to work with documents must therefore suply their own node(s) using an XPath variable (see XPath Variable Bindings).

Action <x:forEach> establishes for its nested actions a specific context for XPath expressions evaluation. See <x:forEach> for details.

11.1.7. Resources Access

XML actions such as <x:parse> and <x:transform> allow the specification of XML and/or XSLT documents as String or Reader objects. Accessing a resource through a URL is therefore handled through the <c:import> action that works seamlessly with the XML tags as shown below:

<c:import url="http://acme.com/productInfo" var="doc">
    <c:param name="productName" value="${product.name}"/>
</c:import>
<x:parse doc="${doc}" var="parsedDoc"/>

To resolve references to external entities, the systemId (<x:parse>) and docSystemId / xsltSystemId (<x:transform>) attributes can be used. For these attributes:

  • Absolute URLs are passed to the parser directly

  • Relative URLs are treated as references to resources (e.g., loaded via ServletContext.getResource()) and loaded using an EntityResolver and URIResolver as necessary

11.1.8. Core Actions

The XML core actions provide "expression language support" for XPath. These actions are therefore similar to the Expression Language support actions <c:out> and <c:set> covered in General-Purpose Actions: core tag library, except that they apply to XPath expressions.

The core XML actions feature one additional action, <x:parse>, to parse an XML document into a data structure that can then be processed by the XPath engine. For example:

<!-- parse an XML document -->
<c:import url="http://acme.com/customer?id=76567" var="doc"/>
<x:parse doc="${doc}" var="parsedDoc"/>

<!-- access XML data via XPath expressions -->
<x:out select="$parsedDoc/name"/>
<x:out select="$parsedDoc/address"/>

<!-- set a scoped variable -->
<x:set var="custName" scope="request" select="$parsedDoc/name"/>

The context for the evaluation of an XPath Expression can be set either directly within the XPath expression (as shown in the example above), or via an ancestor tag that sets a context that can be used by nested tags. An example of this is with action <x:forEach> (see <x:forEach>).

<!-- context set by ancestor tag <x:forEach> -->
<x:forEach select="$parsedDoc//customer">
    <x:out select="name"/>
</x:forEach>

11.2. <x:parse>

Parses an XML document.

Syntax

Syntax 1: XML document specified via a String or Reader object

<x:parse {doc="XMLDocument"|xml[10]="XMLDocument"}
    {var="var" [scope="scope"]|varDom="var" [scopeDom="scope"]}
    [systemId="systemId"]
    [filter="filter"]/>

Syntax 2: XML document specified via the body content

<x:parse
    {var="var" [scope="scope"]|varDom="var" [scopeDom="scope"]}
    [systemId="systemId"]
    [filter="filter"]>
        XML Document to parse
</x:parse>

where scope is {page|request|session|application}

Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

doc

true

String, Reader

Source XML document to be parsed.

xml

true

String, Reader

Deprecated [11]. Use attribute doc instead.

systemId

true

String

The system identifier (URI) for parsing the XML document.

filter

true

org.xml.sax.XMLFilter

Filter to be applied to the source document.

var

false

String

Name of the exported scoped variable for the parsed XML document. The type of the scoped variable is implementation dependent.

scope

false

String

Scope for var.

varDom

false

String

Name of the exported scoped variable for the parsed XML document. The type of the scoped variable is org.w3c.dom.Document.

scopeDom

false

String

Scope for varDom.

Null & Error Handling
  • If the source XML document is null or empty, a JspException is thrown.

  • If filter is null, filtering is not performed.

Description

The <x:parse> action parses an XML document and saves the resulting object in the scoped variable specified by attribute var or varDom. It does not perform any validation against DTDs or Schemas.

The XML document can be specified either with the doc attribute, or inline via the action’s body content.

var and varDom

If var is used, the type of the resulting object is not defined by this specification. This allows implementations to use whatever they deem best for an efficient implementation of the XML tagset. varDom exposes a DOM document, allowing collaboration with custom actions. Objects exposed by var and varDom can both be used to set the context of an XPath expression.

Filtering for Performance Benefits

If an implementation of the XML tagset is based on DOM-like structures, there will be a significant performance impact when dealing with large XML documents. To help with this, attribute filter can be used to allow filtering of the input data prior to having it parsed by the implementation into a DOM-like structure.

For example, if one is interested in processing only the "European" customers which represent only 10% of the original XML document received as input, it will greatly reduce the size and complexity of the resulting DOM structure if all non-European customers are pruned from the XML document prior to parsing.

<c:import url="http://acme.com/customers" var="doc"/>
    <x:parse doc="${doc}" filter="${filterEuropeanCust}"
            var="parsedDoc"/>

The filter attribute accepts an object of type org.xml.sax.XMLFilter.

If configuration of the filter is desirable, it is suggested that the developer of the filter provides a custom tag for easy configuration by a page author.

11.3. <x:out>

Evaluates an XPath expression and outputs the result of the evaluation to the current JspWriter object.

Syntax
<x:out select="XPathExpression" [escapeXml="{true|false}"]/>
Body Content

Empty.

Attributes
Name Dynamic Type Description

select

false

String

XPath expression to be evaluated.

escapeXml

true

boolean

Determines whether characters <,>,&,'," in the resulting string should be converted to their corresponding character entity codes. Default value is true.

Description

The expression to be evaluated is specified via attribute select and must be in XPath syntax. The result of the evaluation is converted to a String as if the XPath string() function were applied, and is subsequently written to the current JspWriter object.

This action is the equivalent of <%=…​%> (display the result of an expression in the Jakarta Server Pages syntax) and <c:out> (display the result of an expression in the expression language syntax).

If escapeXml is true, the following character conversions are applied:

Character Character Entity Code

<

&lt;

>

&gt;

&

&amp;

'

&#039;

"

&#034;

11.4. <x:set>

Evaluates an XPath expression and stores the result into a scoped variable.

Syntax
<x:set select="XPathExpression"
    var="varName" [scope="{page|request|session|application}"]/>
Body Content

Empty.

Attributes
Name Dynamic Type Description

select

false

String

XPath expression to be evaluated.

var

false

String

Name of the exported scoped variable to hold the value specified in the action. The type of the scoped variable is whatever type the select expression evaluates to.

scope

false

String

Scope for var.

Description

Evaluates an XPath expression (specified via attribute select) and stores the result into a scoped variable (specified via attributes var and scope).

The mapping of XPath types to Java types is described in XPath to Java Type Mappings.

12. XML Flow Control Actions: xml tag library

The core set of XML actions provides the basic functionality to easily parse and access XML data. Another important piece of functionality is the ability to iterate over elements in an XML document, as well as conditionally process Jakarta Server Pages code fragments depending on the result of an XPath expression. The XML flow control actions provide these capabilities.

12.1. Overview

The XML flow control actions provide flow control based on the value of XPath expressions. These actions are therefore similar to the Expression Language flow control actions (<c:if>, <c:choose>, and <`c:forEach>`), except that they apply to XPath expressions.

The <x:if> action has a select attribute that specifies an XPath expression. The expression is evaluated and the resulting object is converted to a boolean according to the semantics of the XPath boolean() function:

  • A number is true if an only if it is neither positive or negative zero nor NaN

  • A node-set is true if and only if it is non-empty

  • A string is true if and only if its length is non-zero

<x:if> renders its body if the result is true. For example:

<x:if select="$customer/[location='UK']">
    UK based customer
</x:if>

The <x:choose> action selects one among a number of possible alternatives. It consists of a sequence of <x:when> elements followed by an optional <x:otherwise>. Each <x:when> element has a single attribute, select, which specifies an XPath expression. When a <x:choose> element is processed, each of the <x:when> elements has its expression evaluated in turn, and the resulting object is converted to a boolean according to the semantics of the XPath boolean function. The body of the first, and only the first, <x:when> whose result is true is rendered.

If none of the test conditions of nested <x:when> tags evaluates to true, then the body of an <x:otherwise> tag is evaluated, if present.

<x:choose>
    <x:when select="$customer/firstName">
        Hello <x:out select="$customer/firstName"/>
    </x:when>
    <x:otherwise>
        Hello my friend
    </x:otherwise>
</x:choose>

The <x:forEach> action evaluates the given XPath expression and iterates over the result, setting the context node to each element in the iteration. For example:

<x:forEach select="$doc//author">
    <x:out select="@name"/>
</x:forEach>

12.2. <x:if>

Evaluates the XPath expression specified in the select attribute and renders its body content if the expression evaluates to true.

Syntax

Syntax 1: Without body content

<x:if select="XPathExpression"
        var="varName" [scope="{page|request|session|application}"]/>

Syntax 2: With body content

<x:if select="XPathExpression"
        [var="varName"] [scope="{page|request|session|application}"]>
    body content
</x:if>
Body Content

Jakarta Server Pages content. If the test condition evaluates to true, the Jakarta Server Pages container processes the body content and then writes it to the current JspWriter.

Attributes
Name Dynamic Type Description

select

false

String

The test condition that tells whether or not the body content should be processed.

var

false

String

Name of the exported scoped variable for the resulting value of the test condition. The type of the scoped variable is Boolean.

scope

false

String

Scope for var.

Constraints
  • If scope is specified, var must also be specified.

Description

The XPath expression specified via attribute select is evaluated, and the resulting object is converted to a boolean according to the semantics of the XPath boolean() function. If true, the body content is evaluated by the Jakarta Server Pages container and the result is written to the current JspWriter.

12.3. <x:choose>

Provides the context for mutually exclusive conditional execution.

Syntax
<x:choose>
    body content (<x:when> and <x:otherwise> subtags)
</x:choose>
Body Content

Jakarta Server Pages content. The body content is processed by the Jakarta Server Pages container (at most one of the nested elements will be processed) and written to the current JspWriter.

Constraints
  • The body of the <x:choose> action can only contain:

    • White spaces
      May appear anywhere around the <x:when> and <x:otherwise> subtags.

    • 1 or more <x:when> actions

    • Must all appear before <x:otherwise>

    • 0 or 1 <x:otherwise> action
      Must be the last action nested within <x:choose>

Description

The <x:choose> action processes the body of the first <x:when> action whose test condition evaluates to true. If none of the test conditions of nested <x:when> actions evaluates to true, then the body of an <x:otherwise> action is processed, if present.

12.4. <x:when>

Represents an alternative within an <x:choose> action.

Syntax
<x:when select="XPathExpression">
    body content
</x:when>
Body Content

Jakarta Server Pages content. If this is the first <x:when> action to evaluate to true within <x:choose>, the Jakarta Server Pages container processes the body content and then writes it to the current JspWriter.

Attributes
Name Dynamic Type Description

select

false

String

The test condition that tells whether or not the body content should be processed

Constraints
  • Must have <x:choose> as an immediate parent.

  • Must appear before an <x:otherwise> action that has the same parent.

Description

The XPath expression specified via attribute select is evaluated, and the resulting object is converted to a boolean according to the semantics of the XPath boolean() function. If this is the first <x:when> action to evaluate to true within <x:choose>, the Jakarta Server Pages container processes the body content and then writes it to the current JspWriter.

12.5. <x:otherwise>

Represents the last alternative within a <x:choose> action.

Syntax
<x:otherwise>
    conditional block
</x:otherwise>
Body Content

Jakarta Server Pages content. If no <x:when> action nested within <x:choose> evaluates to true, the Jakarta Server Pages container processes the body content and then writes it to the current JspWriter.

Attributes

None.

Constraints
  • Must have <x:choose> as an immediate parent.

  • Must be the last nested action within <x:choose>.

Description

Within a <x:choose> action, if none of the nested <x:when> test conditions evaluates to true, then the body content of the <x:otherwise> action is evaluated by the Jakarta Server Pages container, and the result is written to the current JspWriter.

12.6. <x:forEach>

Evaluates the given XPath expression and repeats its nested body content over the result, setting the context node to each element in the iteration.

Syntax
<x:forEach [var="varName"] select="XPathExpression">
        [varStatus="varStatusName"]
        [begin="begin"] [end="end"] [step="step"]>
    body content
</x:forEach>
Body Content

Jakarta Server Pages content. As long as there are items to iterate over, the body content is processed by the Jakarta Server Pages container and written to the current JspWriter.

Attributes
Name Dynamic Type Description

var

false

String

Name of the exported scoped variable for the current item of the iteration. This scoped variable has nested visibility. Its type depends on the result of the XPath expression in the select attribute.

select

false

String

XPath expression to be evaluated.

varStatus

false

String

Name of the exported scoped variable for the status of the iteration. Object exported is of type jakarta.servlet.jsp.jstl.core.LoopTagStatus. This scoped variable has nested visibility.

begin

true

int

Iteration begins at the item located at the specified index. First item of the collection has index 0.

end

true

int

Iteration ends at the item located at the specified index (inclusive).

step

true

int

Iteration will only process every step items of the collection, starting with the first one.

Constraints
  • If specified, begin must be >= 0.

  • If end is specified and it is less than begin, the loop is simply not executed.

  • If specified, step must be >= 1

Null & Error Handling
  • If select is empty, a JspException is thrown.

Description

Inside the body of the tag, the context for XPath expression evaluations is obtained as follows:

  • variable, function, and namespace bindings operate as in the rest of the Jakarta Standard Tag Library

  • the context node is the node whose representation would be exposed by 'var' (whether or not the 'var' attribute is specified)

  • the context position is the iteration 'count' (with the same meaning as in <c:forEach>)

  • the context size is equal to the number of nodes in the node-set over which <x:forEach> is iterating

13. XML Transform Actions: xml tag library

The transformation of XML documents using XSLT stylesheets is popular in many web applications. The XML transform actions provide this capability so XSLT transformations can be performed within Jakarta Server Pages.

13.1. Overview

The XML transform actions support the transformation of XML documents with XSLT stylesheets.

In the example below, an external XML document (retrieved from an absolute URL) is transformed by a local XSLT stylesheet (context relative path). The result of the transformation is written to the page.

<c:import url="http://acme.com/customers" var="doc"/>
<c:import url="/WEB-INF/xslt/customerList.xsl" var="xslt"/>
<x:transform doc="${doc}" xslt="${xslt}"/>

It is possible to set transformation parameters via nested <x:param> actions. For example:

<x:transform doc="${doc}" xslt="${xslt}">
    <x:param name="foo" value="foo-value"/>
</x:transform>

It is sometimes the case that the same stylesheet transformation needs to be applied multiple times to different source XML documents. A more efficient approach is to process the transformation stylesheet once, and then save this "transformer" object for successive transformations. The specification allows implementations to support transparent caching of transformer objects to improve performance.

13.2. <x:transform>

Applies an XSLT stylesheet transformation to an XML document.

Syntax

Syntax 1: Without body contentt

<x:transform
        {doc="XMLDocument"|xml[12]="XMLDocument"} xslt="XSLTStylesheet"
        [{docSystemId="XMLSystemId"|xmlSystemId[12]="XMLSystemId"}]
        [xsltSystemId="XSLTSystemId"]
        [{var="varName" [scope="scopeName"]|result="resultObject"}]

Syntax 2: With a body to specify transformation parameters

<x:transform
        {doc="XMLDocument"|xml1="XMLDocument"} xslt="XSLTStylesheet"
        [{docSystemId="XMLSystemId"|xmlSystemId[12]="XMLSystemId"}]
        [xsltSystemId="XSLTSystemId"]
        [{var="varName" [scope="scopeName"]|result="resultObject"}]
    <x:param> actions
</x:transform>

Syntax 3: With a body to specify XML document and optional transformation parameters

<x:transform
        xslt="XSLTStylesheet"
        [{docSystemId="XMLSystemId"|xmlSystemId[12]="XMLSystemId"}]
        xsltSystemId="XSLTSystemId"
        [{var="varName" [scope="scopeName"]|result="resultObject"}]
    XML Document to parse
    optional <x:param> actions
</x:transform>

where scopeName is {page|request|session|application}

Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dyn Type Description

doc

true

String, Reader, javax.xml.transform.Source, org.w3c.dom.Document, or object exported by <x:parse>, <x:set>.

Source XML document to be transformed. (If exported by <x:set>, it must correspond to a well-formed XML document, not a partial document.)

xml

true

String, Reader, javax.xml.transform.Source, org.w3c.dom.Document, or object exported by <x:parse>, <x:set>.

Deprecated [13]. Use attribute doc instead.

xslt

true

String, Reader or javax.xml.transform.Source

Transformation stylesheet as a String, Reader, or Source object.

docSystemId

true

String

The system identifier (URI) for parsing the XML document.

xmlSystemId

true

String

Deprecated 1. Use attribute docSystemId instead.

xsltSystemId

true

String

The system identifier (URI) for parsing the XSLT stylesheet.

var

false

String

Name of the exported scoped variable for the transformed XML document. The type of the scoped variable is org.w3c.dom.Document.

scope

false

String

Scope for var.

result

true

javax.xml.transform.Result

Object that captures or processes the transformation result.

Null & Error Handling
  • If the source XML document is null or empty, a JspException is thrown.

  • If the source XSLT document is null or empty, a JspException is thrown.

Description

The <x:transform> tag applies a transformation to an XML document (attribute doc or the action’s body content), given a specific XSLT stylesheet (attribute xslt). It does not perform any validation against DTD’s or Schemas.

Nothing prevents an implementation from caching Transformer objects across invocations of <x:transform>, though implementations should be careful they take into account both the xslt and xsltSystemId attributes when deciding whether to use a cached Transformer or produce a new one. An implementation may assume that any external entities that were referenced during parsing will not change values during the life of the application.

The result of the transformation is written to the page by default. It is also possible to capture the result of the transformation in two other ways:

  • javax.xml.transform.Result object specified by the result attribute.

  • org.w3c.dom.Document object saved in the scoped variable specified by the var and scope attributes.

13.3. <x:param>

Set transformation parameters. Nested action of <x:transform>.

Syntax

Syntax 1: Parameter value specified in attribute "value"

<x:param name="name" value="value"/>

Syntax 2: Parameter value specified in the body content

<x:param name="name">
    parameter value
</x:param>
Body Content

Jakarta Server Pages content. The Jakarta Server Pages container processes the body content, then the action trims it and processes it further.

Attributes
Name Dynamic Type Description

name

true

String

Name of the transformation parameter.

value

true

Object

Value of the parameter.

Description

The <x:param> action must be nested within <x:transform> to set transformation parameters. The value of the parameter can be specified either via the value attribute, or via the action’s body content.

14. Tag Library Validators

Jakarta Server Pages provides tag library validators (TLVs) as a mechanism for a tag library to enforce constraints on the Jakarta Server Pages document (the "XML view") associated with any Jakarta Server Pages page into which the tag library is imported. While the expectation is that TLVs used by a tag library will typically enforce multi-tag constraints related to usage of the library’s tags themselves, a TLV is free to perform arbitrary validation of Jakarta Server Pages documents. A TLV returns to the container information about which elements, if any, are in violation of its specific constraints, along with textual descriptions of the syntactic violation.

The Jakarta Standard Tag Library provides TLVs that perform "reusable" validation; i.e. generic validation that custom tag-library authors might wish to incorporate in their own tag libraries. These tag libraries do not necessarily need to be substantial collections of tags; a taglib may exist simply to provide site-specific validation logic. Just like tag libraries whose primary focus is to provide new tags, such "validation-centric" tag libraries may be configured and used by "back-end" developers in order to affect the "front-end" Jakarta Server Pages page author’s environment.

This chapter covers the Jakarta Standard Tag Library tag library validators.

14.1. Overview

The Jakarta Standard Tag Library exposes via TLVs two simple types of validations. These TLV classes may be used in custom tag-library descriptors (TLDs) to restrict the page author’s activities. The two types of validation provided in this fashion are:

  • jakarta.servlet.jsp.jstl.tlv.ScriptFree
    Assurance of script-free pages

  • jakarta.servlet.jsp.jstl.tlv.PermittedTaglibs
    Enumeration of permitted tag libraries (including the Jakarta Standard Tag Library) on a page

For example, to prevent a Jakarta Server Pages page from using Jakarta Server Pages scriptlets and Jakarta Server Pages declarations, but still allow expressions, a developer could create the following TLD:

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="https://jakarta.ee/xml/ns/jakartaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-jsptaglibrary_3_0.xsd"
    version="3.0">
    <description>
        Validates Jakarta Server Pages to prohibit use of scripting elements.
    </description>
    <tlib-version>1.0</tlib-version>
    <jsp-version>2.0</jsp.version>
    <short-name>scriptfree</short-name>
    <uri>http://acme.com/scriptfree</uri>

    <validator>
        <validator-class>
            jakarta.servlet.jsp.jstl.tlv.ScriptFreeTLV
        </validator-class>
        <init-param>
            <param-name>allowDeclarations</param-name>
            <param-value>false</param-value>
        </init-param>
        <init-param>
            <param-name>allowScriptlets</param-name>
            <param-value>false</param-value>
        </init-param>
        <init-param>
            <param-name>allowExpressions</param-name>
            <param-value>true</param-value>
        </init-param>
        <init-param>
            <param-name>allowRTExpressions</param-name>
            <param-value>true</param-value>
        </init-param>
    </validator>
</taglib>

Note that in Jakarta Server Pages, scripting elements can also be disabled through the use of the scripting-invalid configuration element (see the Jakarta Server Pages specification for details).

Similarly, to restrict a Jakarta Server Pages page to a set of permitted tag-libraries (in the example below, the Jakarta Standard Tag Library "Expression Language" tag libraries), a developer could create the following TLD:

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="https://jakarta.ee/xml/ns/jakartaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-jsptaglibrary_3_0.xsd"
    version="3.0">
    <description>
        Restricts Jakarta Server Pages to the Jakarta Standard Tag Library tag libraries
    </description>
    <tlib-version>1.0</tlib-version>
    <jsp-version>2.0</jsp.version>
    <short-name>jstl taglibs only</scriptfree>
    <uri>http://acme.com/jstlTaglibsOnly</uri>

    <validator>
        <validator-class>
            jakarta.servlet.jsp.jstl.tlv.PermittedTaglibsTLV
        </validator-class>
        <init-param>
            <param-name>permittedTaglibs</param-name>
            <param-value>
                jakarta.tags.core
                jakarta.tags.xml
                jakarta.tags.fmt
                jakarta.tags.sql
            </param-value>
        </init-param>
    </validator>
</taglib>

15. Functions: function tag library

Just like custom actions allow developers to extend the Jakarta Server Pages syntax with their own customized behavior, the expression language defined in Jakarta Server Pages introduces the notion of functions to allow developers to extend the capabilities of the Expression Language.

The Jakarta Standard Tag Library is about the standardization, via these extension mechanisms, of behavior that is commonly needed by page authors. In addition to defining a standard set of actions, the Jakarta Standard Tag Library therefore also defines a standardized set of Expression Language functions. These functions are described in this chapter.

15.1. Overview

The Jakarta Standard Tag Library functions are all grouped within the function tag library. They cover various domains of functionality described below.

15.1.1. The length Function

A feature sorely missed in JSTL 1.0 was the ability to easily get the size of a collection. While the java.util.Collection interface defines a size() method, it unfortunately does not conform to the JavaBeans architecture design pattern for properties and cannot be accessed via the expression language.

The length function has been designed to be very similar to the use of "length" in EcmaScript. It can be applied to any object supported by the Jakarta Standard Tag Library iteration action <c:forEach>[14] and returns the length of the collection. When applied to a String, it returns the number of characters in the string.

A sample use of length is shown in the example below where scoped variable athletes is a collection of Athletes objects.

There are ${fn:length(athletes)} athletes representing ${country}

15.1.2. String Manipulation Functions

String manipulation functions allow page authors to:

  • Change the capitalization of a string ( toLowerCase, toUpperCase)

  • Get a subset of a string (substring, substringAfter, substringBefore)

  • Trim a string (trim)

  • Replace characters in a string (replace)

  • Check if a string contains another string (indexOf, startsWith, endsWith, contains, containsIgnoreCase)

  • split a string (split) into an array, and join an array into a string (join)

  • Escape XML characters in the string (escapeXml)

The example below shows simple uses of these functions.

<%-- truncate name to 30 chars and display it in uppercase --%>
${fn:toUpperCase(fn:substring(name, 0, 30))}

<%-- Display the text value prior to the first '*' character --%>
${fn:substringBefore(text, '*')}

<%-- Scoped variable "custId" may contain whitespaces at the beginning
or end. Trim it first, otherwise we end up with +'s in the URL --%>
<c:url var="myUrl" value="${base}/cust">
    <c:param name="custId" value="${fn:trim(custId)}"/>
</c:url>

<%-- Display the text in between brackets --%>
${fn:substring(text, fn:indexOf(text, '(')+1,
                     fn:indexOf(text, ')'))}

<%-- Display the name if it contains the search string --%>
<c:if test="${fn:containsIgnoreCase(name, searchString)}">
    Found name: ${name}
</c:if>

<%-- Display the last 10 characters of the text value --%>
${fn:substring(text, fn:length(text)-10)}

<%-- Display text value with bullets instead of '-' --%>
${fn:replace(text, '-', '&#149;')}

While one can always use <c:out> to make sure that XML characters are properly escaped, the function escapeXml provides a syntax that is more concise as can be seen in the following example:

<%-- Escape XML characters when displaying
the value of a request parameter (avoid cross-site scripting) --%>

<input name="userName" value="${fn:escapeXml(param:userName)}">

<%-- Escape XML characters when passing an attribute value to an action --%>

<%-- Using <c:out> with <c:set>--%>
<c:set var="nameEscaped">
    <c:out value="${name}"/>
</c:set>
<my:tag name="${nameEscaped}"/>

<%-- Using <c:out> with <jsp:attribute>--%>
<my:tag>
    <jsp:attribute name="name">
        <c:out value="${name}"/>
    </jsp:attribute>
</my:tag>

<%-- Using fn:escapeXml --%>
<my:tag title="${fn:escapeXml(name)}"/>

15.2. fn:contains

Tests if a string contains the specified substring.

Syntax
fn:contains(string, substring) → boolean
Arguments & Result
Argument Type Description

string

String

The input string on which the function is applied.

substring

String

The substring tested for.

Result

boolean

true if the character sequence represented by the substring argument exists in the character sequence represented by the string argument, false otherwise.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If substring is null, it is processed as an empty string.

Description

Returns true if the character sequence represented by the substring argument exists in the character sequence represented by the string argument, false otherwise.

If substring is empty, this matches the beginning of the string and the value returned is true.

Essentially, fn:contains returns the value of:

     fn:indexOf(string, substring) != -1.

15.3. fn:containsIgnoreCase

Tests if a string contains the specified substring in a case insensitive way.

Syntax
fn:containsIgnoreCase(string, substring) → boolean
Arguments & Result
Argument Type Description

string

String

The input string on which the function is applied.

substring

String

The substring tested for.

Result

boolean

true if the character sequence represented by the substring argument exists in the character sequence represented by the string argument ignoring case differences, false otherwise.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If substring is null, it is processed as an empty string.

Description

The behavior is the same as fn:contains, except that the comparison is done in a case insensitive way, as in:

fn:contains(fn:toUpperCase(string), fn:toUpperCase(substring)).

15.4. fn:endsWith

Tests if a string ends with the specified suffix.

Syntax
fn:endsWith(string, suffix) → boolean
Arguments & Result
Argument Type Description

string

String

The input string on which the function is applied.

suffix

String

The suffix to be matched.

Result

boolean

true if the character sequence represented by the suffix argument is a suffix of the character sequence represented by the string argument, false otherwise.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If substring is null, it is processed as an empty string.

Description

Behavior is similar to fn:startsWith, except that the substring must be at the end of the input string.

If suffix is empty, this matches the end of the string and the value returned is true.

15.5. fn:escapeXml

Escapes characters that could be interpreted as XML markup.

Syntax
fn:escapeXml(string) → String
Arguments & Result
Argument Type Description

string

String

The input string on which the conversion is applied.

Result

String

Converted string.

Null & Error Handling
  • If string is null, it is processed as an empty string.

Description

Escapes characters that could be interpreted as XML markup. The conversions are the same as the ones applied by <c:out> when attribute escapeXml is set to true. See <c:out>.

If string is an empty string, an empty string is returned.

15.6. fn:indexOf

Returns the index within a string of the first occurrence of a specified substring.

Syntax
fn:indexOf(string, substring) → int
Arguments & Result
Argument Type Description

string

String

The input string on which the function is applied.

substring

String

The substring to search for in the input string.

Result

int

If the substring argument is a substring of the input string, returns the index of the first character of the first such substring; if it does not occur as a substring, -1 is returned.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If substring is null, it is processed as an empty string.

Description

Returns the index (0-based) within a string of the first occurrence of a specified substring according to the semantics of method indexOf(substring) of the Java class java.lang.String, with the exception of the "Null and Error Handling" processing described above.

If substring is empty, this matches the beginning of the string and the value returned is 0.

15.7. fn:join

Joins all elements of an array into a string.

Syntax
fn:join(array, separator) → String
Arguments & Result
Argument Type Description

array

String[]

Array of strings to be joined.

separator

String

String to separate each element of the array in the resulting string.

Result

String

All array elements joined into one string.

Null & Error Handling
  • If array is null, an empty string is returned.

  • If separator is null, it is processed as an empty string.

Description

Joins all elements of the string array into a string.

If separator is an empty string, then the elements are joined together without any separator.

15.8. fn:length

Returns the number of items in a collection, or the number of characters in a string.

Syntax
fn:length(input) → integer
Arguments & Result
Argument Type Description

input

Any of the types supported for the items attribute in the <c:forEach> action, or String.

The input collection or string on which the length is computed.

Result

int

Length of the collection or the string.

Null & Error Handling
  • If input is null, it is treated as an empty collection and the value returned is 0.

  • If input is an empty string, the value returned is 0.

15.9. fn:replace

Returns a string resulting from replacing in an input string all occurrences of a "before" substring into an "after" substring.

Syntax
fn:replace(inputString, beforeSubstring, afterSubstring) → String
Arguments & Result
Argument Type Description

inputString

String

The input string on which the replace function is applied.

beforeSubstring

String

The "before" substring to be replaced.

afterSubstring

String

The "after" substring that replaces the "before" substring.

Result

String

The string that results from replacing beforeSubstring with afterSubstring.

Null & Error Handling
  • If inputString is null, it is processed as an empty string.

  • If beforeSubstring is null, it is processed as an empty string.

  • If afterSubstring is null, it is processed as an empty string.

Description

All occurrences of beforeSubstring are replaced by afterSubstring. The text replaced is not reprocessed for further replacements.

If inputstring is an empty string, an empty string is returned.

If beforeSubstring is an empty string, the input string is returned.

If afterSubstring is an empty string, all occurrences of beforeSubstring are removed from inputString.

15.10. fn:split

Splits a string into an array of substrings.

Syntax
fn:split(string, delimiters) → String[]
Arguments & Result
Argument Type Description

string

String

The input string that gets split into an array of substrings.

delimiters

String

Delimiter characters used to split the string.

Result

String[]

Array of strings.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If delimiters is null, it is processed as an empty string.

Description

Breaks a string into tokens according to the semantics of the Java class java.util.StringTokenizer, with the exception of the "Null and Error Handling" described above.

If the input string is empty, the array returned contains one element consisting of an empty string (no splitting occurred, original string is returned).

If delimiters is an empty string, the array returned contains one element consisting of the input string (no splitting occurred, original string is returned).

Delimiter characters themselves are not treated as tokens, and are not included in any token.

15.11. fn:startsWith

Tests if a string starts with the specified prefix.

Syntax
fn:startsWith(string, prefix) → boolean
Arguments & Result
Argument Type Description

string

String

The input string on which the function is applied.

prefix

String

The prefix to be matched.

Result

boolean

true if the character sequence represented by the prefix argument is a prefix of the character sequence represented by the string argument, false otherwise.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If prefix is null, it is processed as an empty string.

Description

Tests if an input string starts with the specified prefix according to the semantics of method startsWith(String prefix) of the Java class java.lang.String, with the exception of the "Null and Error Handling" processing described above.

If prefix is empty, this matches the beginning of the string and the value returned is true.

15.12. fn:substring

Returns a subset of a string.

Syntax
fn:substring(string, beginIndex, endIndex) → String
Arguments & Result
Argument Type Description

string

String

The input string on which the substring function is applied.

beginIndex

int

The beginning index (0-based), inclusive.

endIndex

int

The ending index (0-based), exclusive .

Result

String

The substring of the input string.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If beginIndex is greater than the last index of the input string, an empty string is returned.

  • If beginIndex is less than 0, its value is adjusted to be 0.

  • If endIndex is less than 0 or greater than the length of the input string, its value is adjusted to be the length of the input string (the substring therefore starts at beginIndex and extends to the end of the input string).

  • If endIndex is less than beginIndex, an empty string is returned.

Description

Returns a substring of the input string according to the semantics of method substring() of the Java class java.lang.String, with the exception of the "Null and Error Handling" processing described above.

Using a 0-based indexing scheme, the substring begins at the specified beginIndex and extends to the character at index endIndex -1. The length of the substring is therefore endIndex-beginIndex.

It is suggested to use the value -1 for endIndex to extend the substring to the end of the input string.

15.13. fn:substringAfter

Returns a subset of a string following a specific substring.

Syntax
fn:substringAfter(string, substring) → String
Arguments & Result
Argument Type Description

string

String

The input string on which the substring function is applied.

substring

String

The substring that delimits the beginning of the subset of the input string to be returned.

Result

String

The substring of the input string.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If substring is null, it is processed as an empty string.

Description

The substring returned starts at the first character after the substring matched in the input string, and extends up to the end of the input string.

If string is an empty string, an empty string is returned.

If substring is an empty string, it matches the beginning of the input string and the input string is returned. This is consistent with the behavior of function indexOf, where an empty substring returns index 0.

If substring does not occur in the input string, an empty string is returned.

15.14. fn:substringBefore

Returns a subset of a string before a specific substring.

Syntax
fn:substringBefore(string, substring) → String
Arguments & Result
Argument Type Description

string

String

The input string on which the substring function is applied.

substring

String

The substring that delimits the end of subset of the input string to be returned.

Result

String

The substring of the input string.

Null & Error Handling
  • If string is null, it is processed as an empty string.

  • If substring is null, it is processed as an empty string.

Description

The substring returned starts at the first character in the input string and extends up to the character just before the substring matched in the input string.

If string is an empty string, an empty string is returned.

If substring is an empty string, it matches the beginning of the input string and an empty string is returned. This is consistent with the behavior of function indexOf, where an empty substring returns index 0.

If substring does not occur in the input string, an empty string is returned.

15.15. fn:toLowerCase

Converts all of the characters of a string to lower case.

Syntax
fn:toLowerCase(string) → String
Arguments & Result
Argument Type Description

string

String

The input string on which the transformation to lower case is applied.

Result

String

The input string transformed to lower case.

Null & Error Handling
  • If string is null, it is treated as an empty string and an empty string is returned.

Description

Converts all of the characters of the input string to lower case according to the semantics of method toLowerCase() of the Java class java.lang.String.

15.16. fn:toUpperCase

Converts all of the characters of a string to upper case.

Syntax
fn:toUpperCase(string) → String
Arguments & Result
Argument Type Description

string

String

The input string on which the the transformation to upper case is applied.

Result

String

The input string transformed to upper case.

Null & Error Handling
  • If string is null, it is treated as an empty string and an empty string is returned.

Description

Converts all of the characters of the input string to upper case according to the semantics of method toUpperCase() of the Java class java.lang.String.

15.17. fn:trim

Removes white space from both ends of a string.

Syntax
fn:trim(string) → String
Arguments & Result
Argument Type Description

string

String

The input string on which the the trim is applied.

Result

String

The trimmed string.

Null & Error Handling
  • If string is null, it is treated as an empty string and an empty string is returned.

Description

Removes white space from both ends of a string according to the semantics of method trim() of the Java class java.lang.String.

Appendix A: Compatibility & Migration

This appendix provides information on compatibility between different versions of the Jakarta Standard Tag Library, as well as on how to migrate your web application to take advantage of the new features of the latest Jakarta Standard Tag Library release.

A.1. Java EE Backwards Compatibility

The API has moved from the Java EE (JCP) javax.servlet.jsp.jstl package to the Jakarta EE (Eclipse Foundation) jakarta.servlet.jsp.jstl package. Applications using the Java EE package will need to change this to the Jakarta EE package.

Appendix B: Changes

This appendix lists the changes in the Jakarta Standard Tag Library specification. This appendix is non-normative.

B.1. Changed between Jakarta Standard Tag Library 2.0 and Jakarta Standard Tag Library 3.0

B.2. Changed between Jakarta Standard Tag Library 2.0 and JSR-52

  • The API has moved from the javax.servlet.jsp.jstl package to the jakarta.servlet.jsp.jstl package.

  • The contents of the Javadoc were removed and are now included by reference.



1. Since nested scoped variables are always saved in page scope, no scope attribute is associated with them.
2. It is important to note that the Jakarta Server Pages specification section 1.8.2 says that "A name should refer to a unique object at all points in the execution; that is, all the different scopes really should behave as a single name space." The Jakarta Server Pages specification also says that "A JSP container implementation may or may not enforce this rule explicitly for performance reasons.". Because of this, if a scoped variable with the same name as a nested variable already exists in a scope other than 'page', exactly what happens to that scoped variable depends on how the Jakarta Server Pages container has been implemented. To comply with the Jakarta Server Pages specification, and to avoid non-portable behavior, page authors should therefore avoid using the same name in different scopes.
3. The proper way to process strings of tokens is via <c:forTokens> or via functions split and join.
4. If the responsibility was left to the consumer tag, this could lead to resource leaks (e.g. connection left open, memory space for buffers) until garbage collection is activated. This is because a consumer tag might not close the Reader, or because the page author might remove the consumer tag while leaving inadvertantly the <c:import> tag in the page.
5. This restriction could eventually be lifted when the Jakarta Server Pages spec supports the notion of page events that actions could register to. On a pageExit event, an <c:import> tag would then simply release its resources if it had not already been done, removing the requirement for nested visibility.
6. It is however important to note that using the output of <c:url> as the url attribute value of <c:import> won’t work for context relative URLs (URLs that start with a '/'). That’s because in those cases <c:url> prepends the context path to the URL value.
7. A variant code may also be specified, although rarely used.
8. Four formatting actions localize their data: <fmt:formatNumber>, <fmt:parseNumber>, <fmt:formatDate>, <fmt:parseDate>.
9. <sql:transaction> is responsible for setting the data source in a transaction.
10. Deprecated.
11. Names beginning with the string "xml" are reserved by the XML specification.
12. Deprecated.
13. Names beginning with the string "xml" are reserved by the XML specification.
14. Note that the support in <c:forEach> for strings representing lists of coma separated values has been deprecated. The proper way to process strings of tokens is via <c:forTokens> or via functions split and join.