Running the Enterprise Bean Examples

This chapter describes the Jakarta Enterprise Beans examples. Session beans provide a simple but powerful way to encapsulate business logic within an application. They can be accessed from remote Java clients, web service clients, and components running in the same server.

Overview of the Jakarta Enterprise Beans Examples

In Getting Started with Enterprise Beans, you built a stateless session bean named ConverterBean. This chapter examines the source code of four more session beans:

CartBean: a stateful session bean that is accessed by a remote client
CounterBean: a singleton session bean
HelloServiceBean: a stateless session bean that implements a web service
TimerSessionBean: a stateless session bean that sets a timer

The cart Example

The cart example represents a shopping cart in an online bookstore and uses a stateful session bean to manage the operations of the shopping cart. The bean’s client can add a book to the cart, remove a book, or retrieve the cart’s contents. To assemble cart, you need the following code:

Session bean class (CartBean)
Remote business interface (Cart)

All session beans require a session bean class. All enterprise beans that permit remote access must have a remote business interface. To meet the needs of a specific application, an enterprise bean may also need some helper classes. The CartBean session bean uses two helper classes, BookException and IdVerifier, which are discussed in the section Helper Classes.

The source code for this example is in the jakartaee-examples/tutorial/ejb/cart/ directory.

The Business Interface

The Cart business interface is a plain Java interface that defines all the business methods implemented in the bean class. If the bean class implements a single interface, that interface is assumed to the business interface. The business interface is a local interface unless it is annotated with the jakarta.ejb.Remote annotation; the jakarta.ejb.Local annotation is optional in this case.

The bean class may implement more than one interface. In that case, the business interfaces must either be explicitly annotated @Local or @Remote or be specified by decorating the bean class with @Local or @Remote. However, the following interfaces are excluded when determining whether the bean class implements more than one interface:

java.io.Serializable
java.io.Externalizable
Any of the interfaces defined by the jakarta.ejb package

The source code for the Cart business interface is as follows:

package ee.jakarta.tutorial.cart.ejb;

import cart.util.BookException;
import java.util.List;
import jakarta.ejb.Remote;

@Remote
public interface Cart {
    public void initialize(String person) throws BookException;
    public void initialize(String person, String id) throws BookException;
    public void addBook(String title);
    public void removeBook(String title) throws BookException;
    public List<String> getContents();
    public void remove();
}

Session Bean Class

The session bean class for this example is called CartBean. Like any stateful session bean, the CartBean class must meet the following requirements.

The class is annotated @Stateful.
The class implements the business methods defined in the business interface.

Stateful session beans may also do the following.

Implement the business interface, a plain Java interface. It is good practice to implement the bean’s business interface.
Implement any optional lifecycle callback methods, annotated @PostConstruct, @PreDestroy, @PostActivate, and @PrePassivate.
Implement any optional business methods annotated @Remove.

The source code for the CartBean class is as follows:

package ee.jakarta.tutorial.cart.ejb;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import ee.jakarta.tutorial.cart.util.BookException;
import ee.jakarta.tutorial.cart.util.IdVerifier;
import jakarta.ejb.Remove;
import jakarta.ejb.Stateful;

@Stateful
public class CartBean implements Cart {
    String customerId;
    String customerName;
    List<String> contents;

    @Override
    public void initialize(String person) throws BookException {
        if (person == null) {
            throw new BookException("Null person not allowed.");
        } else {
            customerName = person;
        }
        customerId = "0";
        contents = new ArrayList<>();
    }

    @Override
    public void initialize(String person, String id)
                 throws BookException {
        if (person == null) {
            throw new BookException("Null person not allowed.");
        } else {
            customerName = person;
        }

        IdVerifier idChecker = new IdVerifier();
        if (idChecker.validate(id)) {
            customerId = id;
        } else {
            throw new BookException("Invalid id: " + id);
        }

        contents = new ArrayList<>();
    }

    @Override
    public void addBook(String title) {
        contents.add(title);
    }

    @Override
    public void removeBook(String title) throws BookException {
        boolean result = contents.remove(title);
        if (result == false) {
            throw new BookException("\"" + title + " not in cart.");
        }
    }

    @Override
    public List<String> getContents() {
        return contents;
    }

    @Remove
    @Override
    public void remove() {
        contents = null;
    }
}

Lifecycle Callback Methods

A method in the bean class may be declared as a lifecycle callback method by annotating the method with the following annotations.

jakarta.annotation.PostConstruct: Methods annotated with @PostConstruct are invoked by the container on newly constructed bean instances after all dependency injection has completed and before the first business method is invoked on the enterprise bean.
jakarta.annotation.PreDestroy: Methods annotated with @PreDestroy are invoked after any method annotated @Remove has completed and before the container removes the enterprise bean instance.
jakarta.ejb.PostActivate: Methods annotated with @PostActivate are invoked by the container after the container moves the bean from secondary storage to active status.
jakarta.ejb.PrePassivate: Methods annotated with @PrePassivate are invoked by the container before it passivates the enterprise bean, meaning that the container temporarily removes the bean from the environment and saves it to secondary storage.

Lifecycle callback methods must return void and have no parameters.

Business Methods

The primary purpose of a session bean is to run business tasks for the client. The client invokes business methods on the object reference it gets from dependency injection or JNDI lookup. From the client’s perspective, the business methods appear to run locally, although they run remotely in the session bean. The following code snippet shows how the CartClient program invokes the business methods:

cart.initialize("Duke DeEarl", "123");
...
cart.addBook("Bel Canto");
 ...
List<String> bookList = cart.getContents();
...
cart.removeBook("Gravity's Rainbow");

The CartBean class implements the business methods in the following code:

@Override
public void addBook(String title) {
   contents.add(title);
}

@Override
public void removeBook(String title) throws BookException {
   boolean result = contents.remove(title);
   if (result == false) {
      throw new BookException("\"" + title + "not in cart.");
   }
}

@Override
public List<String> getContents() {
   return contents;
}

The signature of a business method must conform to these rules.

The method name must not begin with ejb, to avoid conflicts with callback methods defined by the Jakarta Enterprise Beans architecture. For example, you cannot call a business method ejbCreate or ejbActivate.
The access control modifier must be public.
If the bean allows remote access through a remote business interface, the arguments and return types must be legal types for the Java Remote Method Invocation (RMI) API.
If the bean is a Jakarta XML Web Services endpoint, the arguments and return types for the methods annotated @WebMethod must be legal types for Jakarta XML Web Services.
If the bean is a Jakarta RESTful Web Services resource, the arguments and return types for the resource methods must be legal types for Jakarta RESTful Web Services.
The modifier must not be static or final.

The throws clause can include exceptions that you define for your application. The removeBook method, for example, throws a BookException if the book is not in the cart.

To indicate a system-level problem, such as the inability to connect to a database, a business method should throw a jakarta.ejb.EJBException. The container will not wrap application exceptions, such as BookException. Because EJBException is a subclass of RuntimeException, you do not need to include it in the throws clause of the business method.

The @Remove Method

Business methods annotated with jakarta.ejb.Remove in the stateful session bean class can be invoked by enterprise bean clients to remove the bean instance. The container will remove the enterprise bean after a @Remove method completes, either normally or abnormally.

In CartBean, the remove method is a @Remove method:

@Remove
@Override
public void remove() {
    contents = null;
}

Helper Classes

The CartBean session bean has two helper classes: BookException and IdVerifier. The BookException is thrown by the removeBook method, and the IdVerifier validates the customerId in one of the create methods. Helper classes may reside in an EJB JAR file that contains the enterprise bean class; a WAR file if the enterprise bean is packaged within a WAR; or an EAR file that contains an EJB JAR, a WAR file, or a separate library JAR file. In cart, the helper classes are included in a library JAR used by the application client and the EJB JAR.

Running the cart Example

Now you are ready to compile the remote interface (Cart.java), the enterprise bean class (CartBean.java), the client class (CartClient.java), and the helper classes (BookException.java and IdVerifier.java).

You can use either NetBeans IDE or Maven to build, package, deploy, and run the cart application.

To Run the cart Example Using NetBeans IDE

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/ejb
```
Select the cart folder.
Select the Open Required Projects check box.
Click Open Project.
In the Projects tab, right-click the cart project and select Build.

This builds and packages the application into cart.ear, located in jakartaee-examples/tutorial/ejb/cart/cart-ear/target/, and deploys this EAR file to your GlassFish Server instance.

You will see the output of the cart-app-client application client in the Output tab:
```
...
Retrieving book title from cart: Infinite Jest
Retrieving book title from cart: Bel Canto
Retrieving book title from cart: Kafka on the Shore
Removing "Gravity's Rainbow" from cart.
Caught a BookException: "Gravity's Rainbow" not in cart.
```

To Run the cart Example Using Maven

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
In a terminal window, go to:
```
jakartaee-examples/tutorial/ejb/cart/
```
Enter the following command:
```
mvn install
```
This command compiles and packages the application into an EAR file, cart.ear, located in the target directory, and deploys the EAR to your GlassFish Server instance.

Then, the client stubs are retrieved and run. This is equivalent to running the following command:
```
appclient -client cart-ear/target/cart-earClient.jar
```
The client JAR, cart-earClient.jar, contains the application client class, the helper class BookException, and the Cart business interface.

When you run the client, the application client container injects any component references declared in the application client class, in this case the reference to the Cart enterprise bean.

You will see the output of the cart-app-client application client in the terminal window:
```
...
Retrieving book title from cart: Infinite Jest
Retrieving book title from cart: Bel Canto
Retrieving book title from cart: Kafka on the Shore
Removing "Gravity's Rainbow" from cart.
Caught a BookException: "Gravity's Rainbow" not in cart.
```

A Singleton Session Bean Example: counter

The counter example demonstrates how to create a singleton session bean.

Creating a Singleton Session Bean

The jakarta.ejb.Singleton annotation is used to specify that the enterprise bean implementation class is a singleton session bean:

@Singleton
public class SingletonBean { ... }

Initializing Singleton Session Beans

The Enterprise Bean container is responsible for determining when to initialize a singleton session bean instance unless the singleton session bean implementation class is annotated with the jakarta.ejb.Startup annotation. In this case, sometimes called eager initialization, the Enterprise Bean container must initialize the singleton session bean upon application startup. The singleton session bean is initialized before the Enterprise Bean container delivers client requests to any enterprise beans in the application. This allows the singleton session bean to perform, for example, application startup tasks.

The following singleton session bean stores the status of an application and is eagerly initialized:

@Startup
@Singleton
public class StatusBean {
  private String status;

  @PostConstruct
  void init {
    status = "Ready";
  }
  ...
}

Sometimes multiple singleton session beans are used to initialize data for an application and therefore must be initialized in a specific order. In these cases, use the jakarta.ejb.DependsOn annotation to declare the startup dependencies of the singleton session bean. The @DependsOn annotation’s value attribute is one or more strings that specify the name of the target singleton session bean. If more than one dependent singleton bean is specified in @DependsOn, the order in which they are listed is not necessarily the order in which the Enterprise Bean container will initialize the target singleton session beans.

The following singleton session bean, PrimaryBean, should be started up first:

@Singleton
public class PrimaryBean { ... }

SecondaryBean depends on PrimaryBean:

@Singleton
@DependsOn("PrimaryBean")
public class SecondaryBean { ... }

This guarantees that the Enterprise Bean container will initialize PrimaryBean before SecondaryBean.

The following singleton session bean, TertiaryBean, depends on PrimaryBean and SecondaryBean:

@Singleton
@DependsOn({"PrimaryBean", "SecondaryBean"})
public class TertiaryBean { ... }

SecondaryBean explicitly requires PrimaryBean to be initialized before it is initialized, through its own @DependsOn annotation. In this case, the Enterprise Bean container will first initialize PrimaryBean, then SecondaryBean, and finally TertiaryBean.

If, however, SecondaryBean did not explicitly depend on PrimaryBean, the Enterprise Bean container may initialize either PrimaryBean or SecondaryBean first. That is, the Enterprise Bean container could initialize the singletons in the following order: SecondaryBean, PrimaryBean, TertiaryBean.

Managing Concurrent Access in a Singleton Session Bean

Singleton session beans are designed for concurrent access, situations in which many clients need to access a single instance of a session bean at the same time. A singleton’s client needs only a reference to a singleton in order to invoke any business methods exposed by the singleton and doesn’t need to worry about any other clients that may be simultaneously invoking business methods on the same singleton.

When creating a singleton session bean, concurrent access to the singleton’s business methods can be controlled in two ways: container-managed concurrency and bean-managed concurrency.

The jakarta.ejb.ConcurrencyManagement annotation is used to specify container-managed or bean-managed concurrency for the singleton. With @ConcurrencyManagement, a type attribute must be set to either jakarta.ejb.ConcurrencyManagementType.CONTAINER or jakarta.ejb.ConcurrencyManagementType.BEAN. If no @ConcurrencyManagement annotation is present on the singleton implementation class, the Enterprise Bean container default of container-managed concurrency is used.

Container-Managed Concurrency

If a singleton uses container-managed concurrency, the Enterprise Bean container controls client access to the business methods of the singleton. The jakarta.ejb.Lock annotation and a jakarta.ejb.LockType type are used to specify the access level of the singleton’s business methods or @Timeout methods. The LockType enumerated types are READ and WRITE.

Annotate a singleton’s business or timeout method with @Lock(LockType.READ) if the method can be concurrently accessed, or shared, with many clients. Annotate the business or timeout method with @Lock(LockType.WRITE) if the singleton session bean should be locked to other clients while a client is calling that method. Typically, the @Lock(LockType.WRITE) annotation is used when clients are modifying the state of the singleton.

Annotating a singleton class with @Lock specifies that all the business methods and any timeout methods of the singleton will use the specified lock type unless they explicitly set the lock type with a method-level @Lock annotation. If no @Lock annotation is present on the singleton class, the default lock type, @Lock(LockType.WRITE), is applied to all business and timeout methods.

The following example shows how to use the @ConcurrencyManagement, @Lock(LockType.READ), and @Lock(LockType.WRITE) annotations for a singleton that uses container-managed concurrency.

Although by default singletons use container-managed concurrency, the @ConcurrencyManagement(CONTAINER) annotation may be added at the class level of the singleton to explicitly set the concurrency management type:

@ConcurrencyManagement(ConcurrencyManagementType.CONTAINER)
@Singleton
public class ExampleSingletonBean {
  private String state;

  @Lock(LockType.READ)
  public String getState() {
    return state;
  }

  @Lock(LockType.WRITE)
  public void setState(String newState) {
    state = newState;
  }
}

The getState method can be accessed by many clients at the same time because it is annotated with @Lock(LockType.READ). When the setState method is called, however, all the methods in ExampleSingletonBean will be locked to other clients because setState is annotated with @Lock(LockType.WRITE). This prevents two clients from attempting to simultaneously change the state variable of ExampleSingletonBean.

The getData and getStatus methods in the following singleton are of type READ, and the setStatus method is of type WRITE:

@Singleton
@Lock(LockType.READ)
public class SharedSingletonBean {
  private String data;
  private String status;

  public String getData() {
    return data;
  }

  public String getStatus() {
    return status;
  }

  @Lock(LockType.WRITE)
  public void setStatus(String newStatus) {
    status = newStatus;
  }
}

If a method is of locking type WRITE, client access to all the singleton’s methods is blocked until the current client finishes its method call or an access timeout occurs. When an access timeout occurs, the Enterprise Bean container throws a jakarta.ejb.ConcurrentAccessTimeoutException. The jakarta.ejb.AccessTimeout annotation is used to specify the number of milliseconds before an access timeout occurs. If added at the class level of a singleton, @AccessTimeout specifies the access timeout value for all methods in the singleton unless a method explicitly overrides the default with its own @AccessTimeout annotation.

The @AccessTimeout annotation can be applied to both @Lock(LockType.READ) and @Lock(LockType.WRITE) methods. The @AccessTimeout annotation has one required element, value, and one optional element, unit. By default, the value is specified in milliseconds. To change the value unit, set unit to one of the java.util.concurrent.TimeUnit constants: NANOSECONDS, MICROSECONDS, MILLISECONDS, or SECONDS.

The following singleton has a default access timeout value of 120,000 milliseconds, or 2 minutes. The doTediousOperation method overrides the default access timeout and sets the value to 360,000 milliseconds, or 6 minutes:

@Singleton
@AccessTimeout(value=120000)
public class StatusSingletonBean {
  private String status;

  @Lock(LockType.WRITE)
  public void setStatus(String new Status) {
    status = newStatus;
  }

  @Lock(LockType.WRITE)
  @AccessTimeout(value=360000)
  public void doTediousOperation {
    ...
  }
}

The following singleton has a default access timeout value of 60 seconds, specified using the TimeUnit.SECONDS constant:

@Singleton
@AccessTimeout(value=60, unit=TimeUnit.SECONDS)
public class StatusSingletonBean { ... }

Bean-Managed Concurrency

Singletons that use bean-managed concurrency allow full concurrent access to all the business and timeout methods in the singleton. The developer of the singleton is responsible for ensuring that the state of the singleton is synchronized across all clients. Developers who create singletons with bean-managed concurrency are allowed to use the Java programming language synchronization primitives, such as synchronization and volatile, to prevent errors during concurrent access.

Add a @ConcurrencyManagement annotation with the type set to ConcurrencyManagementType.BEAN at the class level of the singleton to specify bean-managed concurrency:

@ConcurrencyManagement(ConcurrencyManagementType.BEAN)
@Singleton
public class AnotherSingletonBean { ... }

Handling Errors in a Singleton Session Bean

If a singleton session bean encounters an error when initialized by the Enterprise Bean container, that singleton instance will be destroyed.

Unlike other enterprise beans, once a singleton session bean instance is initialized, it is not destroyed if the singleton’s business or lifecycle methods cause system exceptions. This ensures that the same singleton instance is used throughout the application lifecycle.

The Architecture of the counter Example

The counter example consists of a singleton session bean, CounterBean, and a Jakarta Faces Facelets web front end.

CounterBean is a simple singleton with one method, getHits, that returns an integer representing the number of times a web page has been accessed. Here is the code of CounterBean:

package ee.jakarta.tutorial.counter.ejb;

import jakarta.ejb.Singleton;

/**
 * CounterBean is a simple singleton session bean that records the number
 * of hits to a web page.
 */
@Singleton
public class CounterBean {
    private int hits = 1;

    // Increment and return the number of hits
    public int getHits() {
        return hits++;
    }
}

The @Singleton annotation marks CounterBean as a singleton session bean. CounterBean uses a local, no-interface view.

CounterBean uses the Enterprise Bean container’s default metadata values for singletons to simplify the coding of the singleton implementation class. There is no @ConcurrencyManagement annotation on the class, so the default of container-managed concurrency access is applied. There is no @Lock annotation on the class or business method, so the default of @Lock(WRITE) is applied to the only business method, getHits.

The following version of CounterBean is functionally equivalent to the preceding version:

package ee.jakarta.tutorial.counter.ejb;

import jakarta.ejb.Singleton;
import jakarta.ejb.ConcurrencyManagement;
import static jakarta.ejb.ConcurrencyManagementType.CONTAINER;
import jakarta.ejb.Lock;
import jakarta.ejb.LockType.WRITE;

/**
 * CounterBean is a simple singleton session bean that records the number
 * of hits to a web page.
 */
@Singleton
@ConcurrencyManagement(CONTAINER)
public class CounterBean {
    private int hits = 1;

    // Increment and return the number of hits
    @Lock(WRITE)
    public int getHits() {
        return hits++;
    }
}

The web front end of counter consists of a Jakarta Faces managed bean, Count.java, that is used by the Facelets XHTML files template.xhtml and index.xhtml. The Count Jakarta Faces managed bean obtains a reference to CounterBean through dependency injection. Count defines a hitCount JavaBeans property. When the getHitCount getter method is called from the XHTML files, CounterBean's getHits method is called to return the current number of page hits.

Here’s the Count managed bean class:

@Named
@ConversationScoped
public class Count implements Serializable {
    @EJB
    private CounterBean counterBean;

    private int hitCount;

    public Count() {
        this.hitCount = 0;
    }

    public int getHitCount() {
        hitCount = counterBean.getHits();
        return hitCount;
    }

    public void setHitCount(int newHits) {
        this.hitCount = newHits;
    }
}

The template.xhtml and index.xhtml files are used to render a Facelets view that displays the number of hits to that view. The index.xhtml file uses an expression language statement, #{count.hitCount}, to access the hitCount property of the Count managed bean. Here is the content of index.xhtml:

<html lang="en"
      xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://xmlns.jcp.org/jsf/facelets"
      xmlns:h="http://xmlns.jcp.org/jsf/html">
    <ui:composition template="/template.xhtml">
        <ui:define name="title">
            This page has been accessed #{count.hitCount} time(s).
        </ui:define>
        <ui:define name="body">
            Hooray!
        </ui:define>
    </ui:composition>
</html>

Running the counter Example

You can use either NetBeans IDE or Maven to build, package, deploy, and run the counter example.

To Run the counter Example Using NetBeans IDE

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/ejb
```
Select the counter folder.
Click Open Project.
In the Projects tab, right-click the counter project and select Run.

A web browser will open the URL http://localhost:8080/counter, which displays the number of hits.
Reload the page to see the hit count increment.

To Run the counter Example Using Maven

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

In a terminal window, go to:

jakartaee-examples/tutorial/ejb/counter/

Enter the following command:
```
mvn install
```
This will build and deploy counter to your GlassFish Server instance.
In a web browser, enter the following URL:
```
http://localhost:8080/counter
```
Reload the page to see the hit count increment.

A Web Service Example: helloservice

This example demonstrates a simple web service that generates a response based on information received from the client. HelloServiceBean is a stateless session bean that implements a single method: sayHello. This method matches the sayHello method invoked by the client described in A Simple XML Web Services Application Client.

The Web Service Endpoint Implementation Class

HelloServiceBean is the endpoint implementation class, typically the primary programming artifact for enterprise bean web service endpoints. The web service endpoint implementation class has the following requirements.

The class must be annotated with either the jakarta.jws.WebService or the jakarta.jws.WebServiceProvider annotation.
The implementing class may explicitly reference an SEI through the endpointInterface element of the @WebService annotation but is not required to do so. If no endpointInterface is specified in @WebService, an SEI is implicitly defined for the implementing class.
The business methods of the implementing class must be public and must not be declared static or final.
Business methods that are exposed to web service clients must be annotated with jakarta.jws.WebMethod.
Business methods that are exposed to web service clients must have Jakarta XML Binding-compatible parameters and return types. See the list of Jakarta XML Binding default data type bindings at Types Supported by XML Web Services.
The implementing class must not be declared final and must not be abstract.
The implementing class must have a default public constructor.
The endpoint class must be annotated @Stateless.
The implementing class must not define the finalize method.
The implementing class may use the jakarta.annotation.PostConstruct or jakarta.annotation.PreDestroy annotations on its methods for lifecycle event callbacks.

The @PostConstruct method is called by the container before the implementing class begins responding to web service clients.

The @PreDestroy method is called by the container before the endpoint is removed from operation.

Stateless Session Bean Implementation Class

The HelloServiceBean class implements the sayHello method, which is annotated @WebMethod. The source code for the HelloServiceBean class is as follows:

package ee.jakarta.tutorial.helloservice.ejb;

import jakarta.ejb.Stateless;
import jakarta.jws.WebMethod;
import jakarta.jws.WebService;

@Stateless
@WebService
public class HelloServiceBean {
    private final String message = "Hello, ";

    public void HelloServiceBean() {}

    @WebMethod
    public String sayHello(String name) {
        return message + name + ".";
    }
}

Running the helloservice Example

You can use either NetBeans IDE or Maven to build, package, and deploy the helloservice example. You can then use the Administration Console to test the web service endpoint methods.

To Build, Package, and Deploy the helloservice Example Using NetBeans IDE

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/ejb
```
Select the helloservice folder.
Click Open Project.
In the Projects tab, right-click the helloservice project and select Build.

This builds and packages the application into helloservice.ear, located in jakartaee-examples/tutorial/ejb/helloservice/target/, and deploys this EAR file to GlassFish Server.

To Build, Package, and Deploy the helloservice Example Using Maven

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

In a terminal window, go to:

jakartaee-examples/tutorial/ejb/helloservice/

Enter the following command:
```
mvn install
```
This compiles the source files and packages the application into an enterprise bean JAR file located at jakartaee-examples/tutorial/ejb/helloservice/target/helloservice.jar. Then the enterprise bean JAR file is deployed to GlassFish Server.

Upon deployment, GlassFish Server generates additional artifacts required for web service invocation, including the WSDL file.

To Test the Service without a Client

The GlassFish Server Administration Console allows you to test the methods of a web service endpoint. To test the sayHello method of HelloServiceBean, follow these steps.

Open the Administration Console by opening the following URL in a web browser:
```
http://localhost:4848/
```
In the navigation tree, select the Applications node.
In the Applications table, click the helloservice link.
In the Modules and Components table, click the View Endpoint link.
On the Web Service Endpoint Information page, click the Tester xref:
```
/HelloServiceBeanService/HelloServiceBean?Tester
```
On the Web Service Test Links page, click the non-secure link (the one that specifies port 8080).
On the HelloServiceBeanService Web Service Tester page, under Methods, enter a name as the parameter to the sayHello method.
Click sayHello.

The sayHello Method invocation page opens. Under Method returned, you’ll see the response from the endpoint.

Using the Timer Service

Applications that model business work flows often rely on timed notifications. The timer service of the enterprise bean container enables you to schedule timed notifications for all types of enterprise beans except for stateful session beans. You can schedule a timed notification to occur according to a calendar schedule, at a specific time, after a duration of time, or at timed intervals. For example, you could set timers to go off at 10:30 a.m. on May 23, in 30 days, or every 12 hours.

Enterprise bean timers are either programmatic timers or automatic timers. Programmatic timers are set by explicitly calling one of the timer creation methods of the TimerService interface. Automatic timers are created upon the successful deployment of an enterprise bean that contains a method annotated with the jakarta.ejb.Schedule or jakarta.ejb.Schedules annotations.

Creating Calendar-Based Timer Expressions

Timers can be set according to a calendar-based schedule, expressed using a syntax similar to the UNIX cron utility. Both programmatic and automatic timers can use calendar-based timer expressions. Calendar-Based Timer Attributes shows the calendar-based timer attributes.

Calendar-Based Timer Attributes
Attribute	Description	Default Value	Allowable Values and Examples
`second`	One or more seconds within a minute	`0`	`0` to `59`. For example: `second="30"`.
`minute`	One or more minutes within an hour	`0`	`0` to `59`. For example: `minute="15"`.
`hour`	One or more hours within a day	`0`	`0` to `23`. For example: `hour="13"`.
`dayOfWeek`	One or more days within a week	`*`	`0` to `7` (both 0 and 7 refer to Sunday). For example: `dayOfWeek="3"`. `Sun`, `Mon`, `Tue`, `Wed`, `Thu`, `Fri`, `Sat`. For example: `dayOfWeek="Mon"`.
`dayOfMonth`	One or more days within a month	`*`	`1` to `31`. For example: `dayOfMonth="15"`. `–7` to `–1` (a negative number means the nth day or days before the end of the month). For example: `dayOfMonth="–3"`. `Last`. For example: `dayOfMonth="Last"`. [`1st`, `2nd`, `3rd`, `4th`, `5th`, `Last`] [`Sun`, `Mon`, `Tue`, `Wed`, `Thu`, `Fri`, `Sat`]. For example: `dayOfMonth="2nd Fri"`.
`month`	One or more months within a year	`*`	`1` to `12`. For example: `month="7"`. `Jan`, `Feb`, `Mar`, `Apr`, `May`, `Jun`, `Jul`, `Aug`, `Sep`, `Oct`, `Nov`, `Dec`. For example: `month="July"`.
`year`	A particular calendar year	`*`	A four-digit calendar year. For example: `year="2011"`.

Specifying Multiple Values in Calendar Expressions

You can specify multiple values in calendar expressions, as described in the following sections.

Using Wildcards in Calendar Expressions

Setting an attribute to an asterisk symbol (*) represents all allowable values for the attribute.

The following expression represents every minute:

minute="*"

The following expression represents every day of the week:

dayOfWeek="*"

Specifying a List of Values

To specify two or more values for an attribute, use a comma (,) to separate the values. A range of values is allowed as part of a list. Wildcards and intervals, however, are not allowed.

Duplicates within a list are ignored.

The following expression sets the day of the week to Tuesday and Thursday:

dayOfWeek="Tue, Thu"

The following expression represents 4:00 a.m., every hour from 9:00 a.m. to 5:00 p.m. using a range, and 10:00 p.m.:

hour="4,9-17,22"

Specifying a Range of Values

Use a dash character (-) to specify an inclusive range of values for an attribute. Members of a range cannot be wildcards, lists, or intervals. A range of the form x-x, is equivalent to the single-valued expression x. A range of the form x-y where x is greater than y is equivalent to the expression x-maximumvalue,minimumvalue-y. That is, the expression begins at x, rolls over to the beginning of the allowable values, and continues up to y.

The following expression represents 9:00 a.m. to 5:00 p.m.:

hour="9-17"

The following expression represents Friday through Monday:

dayOfWeek="5-1"

The following expression represents the twenty-fifth day of the month to the end of the month, and the beginning of the month to the fifth day of the month:

dayOfMonth="25-5"

It is equivalent to the following expression:

dayOfMonth="25-Last,1-5"

Specifying Intervals

The forward slash (/) constrains an attribute to a starting point and an interval and is used to specify every N seconds, minutes, or hours within the minute, hour, or day. For an expression of the form x/y, x represents the starting point and y represents the interval. The wildcard character may be used in the x position of an interval and is equivalent to setting x to 0.

Intervals may be set only for second, minute, and hour attributes.

The following expression represents every 10 minutes within the hour:

minute="*/10"

It is equivalent to:

minute="0,10,20,30,40,50"

The following expression represents every 2 hours starting at noon:

hour="12/2"

Programmatic Timers

When a programmatic timer expires (goes off), the container calls the method annotated @Timeout in the bean’s implementation class. The @Timeout method contains the business logic that handles the timed event.

The @Timeout Method

Methods annotated @Timeout in the enterprise bean class must return void and optionally take a jakarta.ejb.Timer object as the only parameter. They may not throw application exceptions:

@Timeout
public void timeout(Timer timer) {
    System.out.println("TimerBean: timeout occurred");
}

Creating Programmatic Timers

To create a timer, the bean invokes one of the create methods of the TimerService interface. These methods allow single-action, interval, or calendar-based timers to be created.

For single-action or interval timers, the expiration of the timer can be expressed as either a duration or an absolute time. The duration is expressed as a the number of milliseconds before a timeout event is triggered. To specify an absolute time, create a java.util.Date object and pass it to the TimerService.createSingleActionTimer or the TimerService.createTimer method.

The following code sets a programmatic timer that will expire in 1 minute (60,000 milliseconds):

long duration = 60000;
Timer timer =
    timerService.createSingleActionTimer(duration, new TimerConfig());

The following code sets a programmatic timer that will expire at 12:05 p.m. on May 1, 2015, specified as a java.util.Date:

SimpleDateFormatter formatter =
    new SimpleDateFormatter("MM/dd/yyyy 'at' HH:mm");
Date date = formatter.parse("05/01/2015 at 12:05");
Timer timer = timerService.createSingleActionTimer(date, new TimerConfig());

For calendar-based timers, the expiration of the timer is expressed as a jakarta.ejb.ScheduleExpression object, passed as a parameter to the TimerService.createCalendarTimer method. The ScheduleExpression class represents calendar-based timer expressions and has methods that correspond to the attributes described in Creating Calendar-Based Timer Expressions.

The following code creates a programmatic timer using the ScheduleExpression helper class:

ScheduleExpression schedule = new ScheduleExpression();
schedule.dayOfWeek("Mon");
schedule.hour("12-17, 23");
Timer timer = timerService.createCalendarTimer(schedule);

For details on the method signatures, see the TimerService API documentation at https://jakarta.ee/specifications/platform/9/apidocs/jakarta/ejb/TimerService.html.

The bean described in The timersession Example creates a timer as follows:

Timer timer = timerService.createTimer(intervalDuration,
        "Created new programmatic timer");

In the timersession example, the method that calls createTimer is invoked in a business method, which is called by a client.

Timers are persistent by default. If the server is shut down or crashes, persistent timers are saved and will become active again when the server is restarted. If a persistent timer expires while the server is down, the container will call the @Timeout method when the server is restarted.

Nonpersistent programmatic timers are created by calling TimerConfig.setPersistent(false) and passing the TimerConfig object to one of the timer-creation methods.

The Date and long parameters of the createTimer methods represent time with the resolution of milliseconds. However, because the timer service is not intended for real-time applications, a callback to the @Timeout method might not occur with millisecond precision. The timer service is for business applications, which typically measure time in hours, days, or longer durations.

Automatic Timers

Automatic timers are created by the Enterprise Bean container when an enterprise bean that contains methods annotated with the @Schedule or @Schedules annotations is deployed. An enterprise bean can have multiple automatic timeout methods, unlike a programmatic timer, which allows only one method annotated with the @Timeout annotation in the enterprise bean class.

Automatic timers can be configured through annotations or through the ejb-jar.xml deployment descriptor.

Adding a @Schedule annotation on an enterprise bean marks that method as a timeout method according to the calendar schedule specified in the attributes of @Schedule.

The @Schedule annotation has elements that correspond to the calendar expressions detailed in Creating Calendar-Based Timer Expressions and the persistent, info, and timezone elements.

The optional persistent element takes a Boolean value and is used to specify whether the automatic timer should survive a server restart or crash. By default, all automatic timers are persistent.

The optional timezone element is used to specify that the automatic timer is associated with a particular time zone. If set, this element will evaluate all timer expressions in relation to the specified time zone, regardless of the time zone in which the Enterprise Bean container is running. By default, all automatic timers set are in relation to the default time zone of the server.

The optional info element is used to set an informational description of the timer. A timer’s information can be retrieved later by using Timer.getInfo.

The following timeout method uses @Schedule to set a timer that will expire every Sunday at midnight:

@Schedule(dayOfWeek="Sun", hour="0")
public void cleanupWeekData() { ... }

The @Schedules annotation is used to specify multiple calendar-based timer expressions for a given timeout method.

The following timeout method uses the @Schedules annotation to set multiple calendar-based timer expressions. The first expression sets a timer to expire on the last day of every month. The second expression sets a timer to expire every Friday at 11:00 p.m.:

@Schedules ({
    @Schedule(dayOfMonth="Last"),
    @Schedule(dayOfWeek="Fri", hour="23")
})
public void doPeriodicCleanup() { ... }

Canceling and Saving Timers

Timers can be cancelled by the following events.

When a single-event timer expires, the Enterprise Bean container calls the associated timeout method and then cancels the timer.
When the bean invokes the cancel method of the Timer interface, the container cancels the timer.

If a method is invoked on a cancelled timer, the container throws the jakarta.ejb.NoSuchObjectLocalException.

To save a Timer object for future reference, invoke its getHandle method and store the TimerHandle object in a database. (A TimerHandle object is serializable.) To reinstantiate the Timer object, retrieve the handle from the database and invoke getTimer on the handle. A TimerHandle object cannot be passed as an argument of a method defined in a remote or web service interface. In other words, remote clients and web service clients cannot access a bean’s TimerHandle object. Local clients, however, do not have this restriction.

Getting Timer Information

In addition to defining the cancel and getHandle methods, the Timer interface defines methods for obtaining information about timers:

public long getTimeRemaining();
public java.util.Date getNextTimeout();
public java.io.Serializable getInfo();

The getInfo method returns the object that was the last parameter of the createTimer invocation. For example, in the createTimer code snippet of the preceding section, this information parameter is a String object with the value created timer.

To retrieve all of a bean’s active timers, call the getTimers method of the TimerService interface. The getTimers method returns a collection of Timer objects.

Transactions and Timers

An enterprise bean usually creates a timer within a transaction. If this transaction is rolled back, the timer creation also is rolled back. Similarly, if a bean cancels a timer within a transaction that gets rolled back, the timer cancellation is rolled back. In this case, the timer’s duration is reset as if the cancellation had never occurred.

In beans that use container-managed transactions, the @Timeout method usually has the Required or RequiresNew transaction attribute to preserve transaction integrity. With these attributes, the Enterprise Bean container begins the new transaction before calling the @Timeout method. If the transaction is rolled back, the container will call the @Timeout method at least one more time.

The timersession Example

The source code for this example is in the jakartaee-examples/tutorial/ejb/timersession/src/main/java/ directory.

TimerSessionBean is a singleton session bean that shows how to set both an automatic timer and a programmatic timer. In the source code listing of TimerSessionBean that follows, the setTimer and @Timeout methods are used to set a programmatic timer. A TimerService instance is injected by the container when the bean is created. Because it’s a business method, setTimer is exposed to the local, no-interface view of TimerSessionBean and can be invoked by the client. In this example, the client invokes setTimer with an interval duration of 8,000 milliseconds, or 8 seconds. The setTimer method creates a new timer by invoking the createTimer method of TimerService. Now that the timer is set, the Enterprise Bean container will invoke the programmaticTimeout method of TimerSessionBean when the timer expires, in about 8 seconds:

...
    public void setTimer(long intervalDuration) {
        logger.log(Level.INFO,
                "Setting a programmatic timeout for {0} milliseconds from now.",
                intervalDuration);
        Timer timer = timerService.createTimer(intervalDuration,
                "Created new programmatic timer");
    }

    @Timeout
    public void programmaticTimeout(Timer timer) {
        this.setLastProgrammaticTimeout(new Date());
        logger.info("Programmatic timeout occurred.");
    }
...

TimerSessionBean also has an automatic timer and timeout method, automaticTimeout. The automatic timer is set to expire every 1 minute and is set by using a calendar-based timer expression in the @Schedule annotation:

...
    @Schedule(minute = "*/1", hour = "*", persistent = false)
    public void automaticTimeout() {
        this.setLastAutomaticTimeout(new Date());
        logger.info("Automatic timeout occured");
    }
...

TimerSessionBean also has two business methods: getLastProgrammaticTimeout and getLastAutomaticTimeout. Clients call these methods to get the date and time of the last timeout for the programmatic timer and automatic timer, respectively.

Here’s the source code for the TimerSessionBean class:

package ee.jakarta.tutorial.timersession.ejb;

import java.util.Date;
import java.util.logging.Level;
import java.util.logging.Logger;
import jakarta.annotation.Resource;
import jakarta.ejb.Schedule;
import jakarta.ejb.Singleton;
import jakarta.ejb.Startup;
import jakarta.ejb.Timeout;
import jakarta.ejb.Timer;
import jakarta.ejb.TimerService;

@Singleton
@Startup
public class TimerSessionBean {
    @Resource
    TimerService timerService;

    private Date lastProgrammaticTimeout;
    private Date lastAutomaticTimeout;

    private static final Logger logger =
            Logger.getLogger("timersession.ejb.TimerSessionBean");

    public void setTimer(long intervalDuration) {
        logger.log(Level.INFO,
                "Setting a programmatic timeout for {0} milliseconds from now.",
                intervalDuration);
        Timer timer = timerService.createTimer(intervalDuration,
                "Created new programmatic timer");
    }

    @Timeout
    public void programmaticTimeout(Timer timer) {
        this.setLastProgrammaticTimeout(new Date());
        logger.info("Programmatic timeout occurred.");
    }

    @Schedule(minute = "*/1", hour = "*", persistent = false)
    public void automaticTimeout() {
        this.setLastAutomaticTimeout(new Date());
        logger.info("Automatic timeout occured");
    }

    public String getLastProgrammaticTimeout() {
        if (lastProgrammaticTimeout != null) {
            return lastProgrammaticTimeout.toString();
        } else {
            return "never";
        }
    }

    public void setLastProgrammaticTimeout(Date lastTimeout) {
        this.lastProgrammaticTimeout = lastTimeout;
    }

    public String getLastAutomaticTimeout() {
        if (lastAutomaticTimeout != null) {
            return lastAutomaticTimeout.toString();
        } else {
            return "never";
        }
    }

    public void setLastAutomaticTimeout(Date lastAutomaticTimeout) {
        this.lastAutomaticTimeout = lastAutomaticTimeout;
    }
}

GlassFish Server has a default minimum timeout value of 1,000 milliseconds, or 1 second. If you need to set the timeout value lower than 1,000 milliseconds, change the value of the Minimum Delivery Interval setting in the Administration Console.

To modify the minimum timeout value, in the Administration Console expand Configurations, then expand server-config, select EJB Container, and click the EJB Timer Service tab. Enter a new timeout value under Minimum Delivery Interval and click Save.

The lowest practical value for minimum-delivery-interval-in-millis is around 10 milliseconds, owing to virtual machine constraints.

Running the timersession Example

You can use either NetBeans IDE or Maven to build, package, deploy, and run the timersession example.

To Run the timersession Example Using NetBeans IDE

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/ejb
```
Select the timersession folder.
Click Open Project.
From the Run menu, choose Run Project.

This builds and packages the application into a WAR file located at jakartaee-examples/tutorial/ejb/timersession/target/timersession.war, deploys this WAR file to your GlassFish Server instance, and then runs the web client.

To Build, Package, and Deploy the timersession Example Using Maven

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

In a terminal window, go to:

jakartaee-examples/tutorial/ejb/timersession/

Enter the following command:
```
mvn install
```
This builds and packages the application into a WAR file located at jakartaee-examples/tutorial/ejb/timersession/target/timersession.war and deploys this WAR file to your GlassFish Server instance.

To Run the Web Client

Open a web browser to the following URL:
```
http://localhost:8080/timersession
```
Click Set Timer to set a programmatic timer.
Wait for a while and click the browser’s Refresh button.

You will see the date and time of the last programmatic and automatic timeouts.

To see the messages that are logged when a timeout occurs, open the server.log file located in domain-dir/logs/.

Handling Exceptions

The exceptions thrown by enterprise beans fall into two categories: system and application.

A system exception indicates a problem with the services that support an application. For example, a connection to an external resource cannot be obtained, or an injected resource cannot be found. If it encounters a system-level problem, your enterprise bean should throw a jakarta.ejb.EJBException. Because the EJBException is a subclass of RuntimeException, you do not have to specify it in the throws clause of the method declaration. If a system exception is thrown, the Jakarta Enterprise Beans container might destroy the bean instance. Therefore, a system exception cannot be handled by the bean’s client program, but instead requires intervention by a system administrator.

An application exception signals an error in the business logic of an enterprise bean. Application exceptions are typically exceptions that you’ve coded yourself, such as the BookException thrown by the business methods of the CartBean example. When an enterprise bean throws an application exception, the container does not wrap it in another exception. The client should be able to handle any application exception it receives.

If a system exception occurs within a transaction, the Enterprise Bean container rolls back the transaction. However, if an application exception is thrown within a transaction, the container does not roll back the transaction.