Interface | Description |
---|---|
ELContextListener |
The listener interface for receiving notification when an
ELContext is created. |
Class | Description |
---|---|
ArrayELResolver |
Defines property resolution behavior on arrays.
|
BeanELResolver |
Defines property resolution behavior on objects using the JavaBeans component architecture.
|
BeanNameELResolver |
An
ELResolver for resolving user or container managed beans. |
BeanNameResolver |
Resolves a bean by its known name.
|
CompositeELResolver |
Maintains an ordered composite list of child
ELResolver s. |
ELClass |
A runtime representation of a Class in the Jakarta Expression Language expressions.
|
ELContext |
Context information for expression parsing and evaluation.
|
ELContextEvent |
An event which indicates that an
ELContext has been created. |
ELManager |
Manages Jakarta Expression Language parsing and evaluation environment.
|
ELProcessor |
Provides an API for using Jakarta Expression Language in a stand-alone environment.
|
ELResolver |
Enables customization of variable, property, method call, and type conversion resolution behavior for Jakarta
Expression Language expression evaluation.
|
EvaluationListener |
The listener interface for receiving notification when a Jakarta Expression Language expression is evaluated.
|
Expression |
Base class for the expression subclasses
ValueExpression and MethodExpression , implementing
characteristics common to both. |
ExpressionFactory |
Provides an implementation for creating and evaluating Jakarta Expression Language expressions.
|
FunctionMapper |
The interface to a map between Jakarta Expression Language function names and methods.
|
ImportHandler |
Handles imports of class names and package names.
|
LambdaExpression |
Encapsulates a parameterized
ValueExpression . |
ListELResolver |
Defines property resolution behavior on instances of
List . |
MapELResolver |
Defines property resolution behavior on instances of
Map . |
MethodExpression |
An
Expression that refers to a method on an object. |
MethodInfo |
Holds information about a method that a
MethodExpression evaluated to. |
ResourceBundleELResolver |
Defines property resolution behavior on instances of
ResourceBundle . |
StandardELContext |
A standard ELContext suitable for use in a stand alone environment.
|
StaticFieldELResolver |
An
ELResolver for resolving static fields, enum constants and static methods. |
TypeConverter |
A convenient class for writing an ELResolver to do custom type conversions.
|
ValueExpression |
An
Expression that can get or set a value. |
ValueReference |
This encapsulates a base model object and one of its properties.
|
VariableMapper |
The interface to a map between Jakarta Expression Language variables and the Jakarta Expression Language expressions
they are associated with.
|
Exception | Description |
---|---|
ELException |
Represents any of the exception conditions that can arise during expression evaluation.
|
MethodNotFoundException |
Thrown when a method could not be found while evaluating a
MethodExpression . |
PropertyNotFoundException |
Thrown when a property could not be found while evaluating a
ValueExpression or MethodExpression . |
PropertyNotWritableException |
Thrown when a property could not be written to while setting the value on a
ValueExpression . |
Jakarta Expression Language is a simple language originally designed to satisfy the specific needs of web application developers. It has evolved into its own specification intended for general use inside and outside of the web containers.
This package contains the classes and interfaces that describe and define the programmatic access to the Jakarta Expression Language engine. The API is logically partitioned as follows:
An important goal of Jakarta Expression Language is to ensure it can be used in a variety of environments. It must therefore provide enough flexibility to adapt to the specific requirements of the environment where it is being used.
Class ELContext
is what links
the Jakarta Expression Language with the specific environment where it is being used.
It provides the mechanism through which all relevant context for creating or
evaluating an expression is specified.
When Jakarta Expression Language is used in a web container, the creation of ELContext
objects is controlled through the underlying technology.
For example, in Jakarta Server Pages, the
JspContext.getELContext()
factory method is used. In an
stand-alone environment, a default StandardELContext
is
provided.
Some technologies provide the ability to add an ELContextListener
so that applications and frameworks can ensure their own context objects
are attached to any newly created ELContext
.
At the core of the Expression Language is the notion of an expression that gets parsed according to the grammar defined by the Expression Language.
There are two types of expressions defined by Jakarta Expression Language: value expressions
and method expressions. A ValueExpression
such as
"${customer.name}"
can be used either
as an rvalue (return the value associated with property name
of the model object customer
) or as an lvalue
(set the value of the property name
of the model object
customer
).
A MethodExpression
such as
"${handler.process}"
makes it possible to invoke a method
(process
) on a specific model object (handler
).
In version 2.2 and later, either type of Jakarta Expression Language expression can represent a method
invocation, such as ${trader.buy("JAVA")}
, where the arguments to
the method invocation are specified in the expression.
All expression classes extend the base class Expression
, making them
serializable and forcing them to implement equals()
and
hashCode()
. Moreover, each method on these expression classes
that actually evaluates an expression receives a parameter
of class ELContext
,
which provides the context required to evaluate the expression.
An expression is created through the ExpressionFactory
class.
The factory provides two creation methods; one for each type of expression
supported by Jakarta Expression Language.
To create an expression, one must provide an ELContext
,
a string representing
the expression, and the expected type (ValueExpression
) or signature
(MethodExpression
).
The ELContext
provides the context necessary to parse an expression.
Specifically, if the expression uses a Jakarta Expression Language function
(for example ${fn:toUpperCase(customer.name)}
) or a Jakarta Expression Language
variable, then FunctionMapper
and VariableMapper
objects must be available within the ELContext
so that Jakarta Expression Language
functions and Jakarta Expression Language variables are properly mapped.
The creation and the evaluation of an expression are done in two separate
steps. At the evaluation of an expression, the ELContext
provides the context necessary to support property and method resolution
for modal objects.
A deferred expression is one that is created but not immediately evaluated. In a Jakarta Faces request processing life cycle, Jakarta Expression Language expressions are typically created in the tree building phase and evaluated in the rendering phrase.
Adding parameters to a ValueExpression
further enhances the
power of deferred expressions. The LambdaExpression
encapsulates such a construct. A LambdaExpression
can be
invoked by supplying the actual parameters at evaluation. It plays
an important role in the support for collections operators.
By registering EvaluationListener
s in ELContext, a user can
receive notifications during the Jakarta Expression Language expression evaluations.
There are three events that trigger the notification:
Through the ELResolver
base class, Jakarta Expression Language
features a pluggable mechanism to resolve model object references as well as properties
and method invocations of these objects.
The Jakarta Expression Language API provides implementations of ELResolver
supporting
property resolution for common data types which include arrays
(ArrayELResolver
), JavaBeans (BeanELResolver
), List
s (ListELResolver
),
Map
s (MapELResolver
), and ResourceBundle
s (ResourceBundleELResolver
).
Tools can easily obtain more information about resolvable model objects and their
resolvable properties by calling
method getFeatureDescriptors
on the ELResolver
. This method exposes objects
of type java.beans.FeatureDescriptor
, providing all information of interest
on top-level model objects as well as their properties.
If a Jakarta Expression Language expression uses a function
(for example ${fn:toUpperCase(customer.name)}
), then a
FunctionMapper
object must also be specified within
the ELContext
.
The FunctionMapper
is responsible to map
${prefix:name()}
style functions to
static methods that can execute the specified functions.
Just like FunctionMapper
provides
a flexible mechanism to add functions to Jakarta Expression Language,
VariableMapper
provides a flexible mechanism to support the notion of
Jakarta Expression Language variables.
A Jakarta Expression Language variable does not directly refer to a model object that can then
be resolved by an ELResolver
. Instead, it refers to a Jakarta Expression Language
expression. The evaluation of that Jakarta Expression Language expression gives the
Jakarta Expression Language variable its value.
For example, in the following code snippet
<h:inputText value="#{handler.customer.name}"/>
handler
refers to a model object that can be resolved by a Jakarta Expression Language Resolver.
However, in this other example:
<c:forEach var="item" items="#{model.list}"> <h:inputText value="#{item.name}"/> </c:forEach>
item
is a Jakarta Expression Language variable because it does not refer directly to a model
object. Instead, it refers to another Jakarta Expression Language expression, namely a
specific item in the collection referred to by the Jakarta Expression Language expression
#{model.list}
.
Assuming that there are three elements in ${model.list}
, this means
that for each invocation of <h:inputText>
, the following information
about item
must be preserved in the VariableMapper
:
first invocation:item
maps to first element in${model.list}
second invocation:item
maps to second element in${model.list}
third invocation:item
maps to third element in${model.list}
VariableMapper
provides the mechanisms required to allow the mapping
of a Jakarta Expression Language variable to the Jakarta Expression Language expression from which it gets its value.
Jakarta Expression Language 3.0 includes APIs for using Jakarta Expression Language in a stand-alone environment.
ELProcessor
provides simple APIs for the direct
evaluations of expressions. It also makes it easy to define functions,
set variables, and define beans locally.
ELManager
provides lower level APIs for managing the Jakarta Expression Language
parsing and evaluation environment. It contains a default ELContext StandardELContext
.
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