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The Java EE 6 Tutorial

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>