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The Java EE 6 Tutorial

An Application That Uses the JMS API with an Entity

This section explains how to write, compile, package, deploy, and run an application that uses the JMS API with an entity. The application uses the following components:

You will find the source files for this section in the directory tut-install/examples/jms/clientmdbentity/. Path names in this section are relative to this directory.

Overview of the clientmdbentity Example Application

This application simulates, in a simplified way, the work flow of a company’s human resources (HR) department when it processes a new hire. This application also demonstrates how to use the Java EE platform to accomplish a task that many JMS applications need to perform.

A JMS client must often wait for several messages from various sources. It then uses the information in all these messages to assemble a message that it then sends to another destination. The common term for this process is joining messages. Such a task must be transactional, with all the receives and the send as a single transaction. If not all the messages are received successfully, the transaction can be rolled back. For an application client example that illustrates this task, see A Local Transaction Example.

A message-driven bean can process only one message at a time in a transaction. To provide the ability to join messages, an application can have the message-driven bean store the interim information in an entity. The entity can then determine whether all the information has been received; when it has, the entity can report this back to one of the message-driven beans, which then creates and sends the message to the other destination. After it has completed its task, the entity can be removed.

The basic steps of the application are as follows.

  1. The HR department’s application client generates an employee ID for each new hire and then publishes a message (M1) containing the new hire’s name, employee ID, and position. The client then creates a temporary queue, ReplyQueue, with a message listener that waits for a reply to the message. (See Creating Temporary Destinations for more information.)

  2. Two message-driven beans process each message: One bean, OfficeMDB, assigns the new hire’s office number, and the other bean, EquipmentMDB, assigns the new hire’s equipment. The first bean to process the message creates and persists an entity named SetupOffice, then calls a business method of the entity to store the information it has generated. The second bean locates the existing entity and calls another business method to add its information.

  3. When both the office and the equipment have been assigned, the entity business method returns a value of true to the message-driven bean that called the method. The message-driven bean then sends to the reply queue a message (M2) describing the assignments. Then it removes the entity. The application client’s message listener retrieves the information.

Figure 31–4 illustrates the structure of this application. Of course, an actual HR application would have more components; other beans could set up payroll and benefits records, schedule orientation, and so on.

Figure 31–4 assumes that OfficeMDB is the first message-driven bean to consume the message from the client. OfficeMDB then creates and persists the SetupOffice entity and stores the office information. EquipmentMDB then finds the entity, stores the equipment information, and learns that the entity has completed its work. EquipmentMDB then sends the message to the reply queue and removes the entity.

Figure 31–4 An Enterprise Bean Application: Client to Message-Driven Beans to Entity

Diagram of application showing an application client, two message-driven beans, and an entity

Writing the Application Components for the clientmdbentity Example

Writing the components of the application involves coding the application client, the message-driven beans, and the entity class.

Coding the Application Client: HumanResourceClient.java

    The application client, clientmdbentity-app-client/src/java/HumanResourceClient.java, performs the following steps:

  1. Injects ConnectionFactory and Topic resources

  2. Creates a TemporaryQueue to receive notification of processing that occurs, based on new-hire events it has published

  3. Creates a MessageConsumer for the TemporaryQueue, sets the MessageConsumer’s message listener, and starts the connection

  4. Creates a MessageProducer and a MapMessage

  5. Creates five new employees with randomly generated names, positions, and ID numbers (in sequence) and publishes five messages containing this information

The message listener, HRListener, waits for messages that contain the assigned office and equipment for each employee. When a message arrives, the message listener displays the information received and determines whether all five messages have arrived. When they have, the message listener notifies the main method, which then exits.

Coding the Message-Driven Beans for the clientmdbentity Example

This example uses two message-driven beans:

    The beans take the following steps:

  1. They inject MessageDrivenContext and ConnectionFactory resources.

  2. The onMessage method retrieves the information in the message. The EquipmentMDB’s onMessage method chooses equipment, based on the new hire’s position; the OfficeMDB’s onMessage method randomly generates an office number.

  3. After a slight delay to simulate real world processing hitches, the onMessage method calls a helper method, compose.

  4. The compose method takes the following steps:

    1. It either creates and persists the SetupOffice entity or finds it by primary key.

    2. It uses the entity to store the equipment or the office information in the database, calling either the doEquipmentList or the doOfficeNumber business method.

    3. If the business method returns true, meaning that all of the information has been stored, it creates a connection and a session, retrieves the reply destination information from the message, creates a MessageProducer, and sends a reply message that contains the information stored in the entity.

    4. It removes the entity.

Coding the Entity Class for the clientmdbentity Example

The SetupOffice class, clientmdbentity-ejb/src/java/eb/SetupOffice.java, is an entity class. The entity and the message-driven beans are packaged together in an EJB JAR file. The entity class is declared as follows:

@Entity
public class SetupOffice implements Serializable {

The class contains a no-argument constructor and a constructor that takes two arguments, the employee ID and name. It also contains getter and setter methods for the employee ID, name, office number, and equipment list. The getter method for the employee ID has the @Id annotation to indicate that this field is the primary key:

@Id public String getEmployeeId() {
    return id;
}

The class also implements the two business methods, doEquipmentList and doOfficeNumber, and their helper method, checkIfSetupComplete.

The message-driven beans call the business methods and the getter methods.

The persistence.xml file for the entity specifies the most basic settings:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 
             xmlns="http://java.sun.com/xml/ns/persistence" 
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
               http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name="clientmdbentity-ejbPU" transaction-type="JTA">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <jta-data-source>jdbc/__default</jta-data-source>
    <class>eb.SetupOffice</class>
    <properties>
      <property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
    </properties>
  </persistence-unit>
</persistence>

Creating Resources for the clientmdbentity Example

This example uses the connection factory jms/ConnectionFactory and the topic jms/Topic, both of which you used in An Application That Uses the JMS API with a Session Bean. It also uses the JDBC resource named jdbc/__default, which is enabled by default when you start the GlassFish Server.

If you deleted the connection factory or topic, you can create them again using targets in the build.xml file for this example. Use the following commands to create the resources:


ant create-cf
ant create-topic

ProcedureTo Build, Package, Deploy, and Run the clientmdbentity Example Using NetBeans IDE

  1. In NetBeans IDE, select File->Open Project.

  2. In the Open Project dialog, navigate to:


    tut-install/examples/jms/

  3. Select the clientmdbentity folder.

  4. Select the Open as Main Project check box and the Open Required Projects check box.

  5. Click Open Project.

  6. In the Projects tab, right-click the clientmdbentity project and select Build.

    This task creates the following:

    • An application client JAR file that contains the client class and listener class files, along with a manifest file that specifies the main class

    • An EJB JAR file that contains the message-driven beans and the entity class, along with the persistence.xml file

    • An application EAR file that contains the two JAR files along with an application.xml file

  7. If the Java DB database is not already running, follow these steps:

    1. Click the Services tab.

    2. Expand the Databases node.

    3. Right-click the Java DB node and select Start Server.

  8. In the Projects tab, right-click the project and select Run.

    This command deploys the project, returns a client JAR file named clientmdbentityClient.jar and then executes it.

    The output of the application client in the Output pane looks something like this:


    PUBLISHER: Setting hire ID to 50, name Bill Tudor, position Programmer
PUBLISHER: Setting hire ID to 51, name Carol Jones, position Senior Programmer
PUBLISHER: Setting hire ID to 52, name Mark Wilson, position Manager
PUBLISHER: Setting hire ID to 53, name Polly Wren, position Senior Programmer
PUBLISHER: Setting hire ID to 54, name Joe Lawrence, position Director
Waiting for 5 message(s)
New hire event processed:
  Employee ID: 52
  Name: Mark Wilson
  Equipment: PDA
  Office number: 294
Waiting for 4 message(s)
New hire event processed:
  Employee ID: 53
  Name: Polly Wren
  Equipment: Laptop
  Office number: 186
Waiting for 3 message(s)
New hire event processed:
  Employee ID: 54
  Name: Joe Lawrence
  Equipment: Java Phone
  Office number: 135
Waiting for 2 message(s)
New hire event processed:
  Employee ID: 50
  Name: Bill Tudor
  Equipment: Desktop System
  Office number: 200
Waiting for 1 message(s)
New hire event processed:
  Employee ID: 51
  Name: Carol Jones
  Equipment: Laptop
  Office number: 262

    The output from the message-driven beans and the entity class appears in the server log, wrapped in logging information.

    For each employee, the application first creates the entity and then finds it. You may see runtime errors in the server log, and transaction rollbacks may occur. The errors occur if both of the message-driven beans discover at the same time that the entity does not yet exist, so they both try to create it. The first attempt succeeds, but the second fails because the bean already exists. After the rollback, the second message-driven bean tries again and succeeds in finding the entity. Container-managed transactions allow the application to run correctly, in spite of these errors, with no special programming.

    You can run the application client repeatedly.

ProcedureTo Build, Package, Deploy, and Run the clientmdbentity Example Using Ant

  1. Go to the following directory:

    tut-install/examples/jms/clientmdbentity/

  2. To compile the source files and package the application, use the following command:


    ant

    The ant command creates the following:

    • An application client JAR file that contains the client class and listener class files, along with a manifest file that specifies the main class

    • An EJB JAR file that contains the message-driven beans and the entity class, along with the persistence.xml file

    • An application EAR file that contains the two JAR files along with an application.xml file

  3. To deploy the application and run the client, use the following command:


    ant run

    This command starts the database server if it is not already running, then deploys and runs the application.

    Ignore the message that states that the application is deployed at a URL.

    The output in the terminal window looks something like this (preceded by application client container output):


    running application client container.
PUBLISHER: Setting hire ID to 50, name Bill Tudor, position Programmer
PUBLISHER: Setting hire ID to 51, name Carol Jones, position Senior Programmer
PUBLISHER: Setting hire ID to 52, name Mark Wilson, position Manager
PUBLISHER: Setting hire ID to 53, name Polly Wren, position Senior Programmer
PUBLISHER: Setting hire ID to 54, name Joe Lawrence, position Director
Waiting for 5 message(s)
New hire event processed:
  Employee ID: 52
  Name: Mark Wilson
  Equipment: PDA
  Office number: 294
Waiting for 4 message(s)
New hire event processed:
  Employee ID: 53
  Name: Polly Wren
  Equipment: Laptop
  Office number: 186
Waiting for 3 message(s)
New hire event processed:
  Employee ID: 54
  Name: Joe Lawrence
  Equipment: Java Phone
  Office number: 135
Waiting for 2 message(s)
New hire event processed:
  Employee ID: 50
  Name: Bill Tudor
  Equipment: Desktop System
  Office number: 200
Waiting for 1 message(s)
New hire event processed:
  Employee ID: 51
  Name: Carol Jones
  Equipment: Laptop
  Office number: 262

    The output from the message-driven beans and the entity class appears in the server log, wrapped in logging information.

    For each employee, the application first creates the entity and then finds it. You may see runtime errors in the server log, and transaction rollbacks may occur. The errors occur if both of the message-driven beans discover at the same time that the entity does not yet exist, so they both try to create it. The first attempt succeeds, but the second fails because the bean already exists. After the rollback, the second message-driven bean tries again and succeeds in finding the entity. Container-managed transactions allow the application to run correctly, in spite of these errors, with no special programming.

    You can run the application client repeatedly.