Develop an enterprise application to use message-driven beans

Develop an enterprise application to use message-driven beans

Use this task to develop an enterprise application to use a message-driven bean. The message-driven bean is invoked by a J2C activation specification or a JMS listener when a message arrives on the input destination that the listener is monitoring.

Overview

You are recommended to develop the message-driven bean to delegate the business processing of incoming messages to another enterprise bean, to provide clear separation of message handling and business processing. This also enables the business processing to be invoked by either the arrival of incoming messages or, for example, from a WebSphere J2EE client. Responses can be handled by another enterprise bean acting as a sender bean, or handled in the message-driven bean.
You develop an enterprise application to use a message-driven bean like any other enterprise bean, except that a message-driven bean does not have a home interface or a remote interface.
For more information about writing the message-driven bean class, see Creating a message-driven bean in the Rational Application Developer help bookshelf.
To develop an enterprise application to use a message-driven bean, complete the following steps:

Procedure
Create the Enterprise Application project.
Create the message-driven bean class.
You can use the New Enterprise Bean wizard of Rational Application Developer to create an enterprise bean with a bean type of Message-driven bean. The wizard creates appropriate methods for the type of bean. By convention, the message bean class is named nameBean, where name is the name you assign to the message bean; for example:
public class MyJMSppMDBBean implements MessageDrivenBean, javax.jms.MessageListener
All message-driven beans must implement the MessageDrivenBean interface. For JMS messaging, a message-driven bean must also implement the message listener interface, javax.jms.MessageListener. Other JCA-compliant Resource Adapters may provide their own message listener interface that needs to be implemented.
A message-driven bean can be registered with the EJB timer service for time-based event notifications if it also implements the javax.ejb.TimedObject interface and the timer callback method void ejbTimeout(Timer). At the scheduled time, the container invokes the message-driven bean’s ejbTimeout method. The message-driven bean class must define and implement the following methods:

onMessage(message), which must meet the following requirements:

The method must have a single argument of type javax.jms.Message.

The throws clause must not define any application exceptions.

If the message-driven bean is configured to use bean-managed transactions, it must call the javax.transaction.UserTransaction interface to scope the transactions. Because these calls occur inside the onMessage() method, the transaction scope does not include the initial message receipt. For more information, see Message-driven beans - transaction support.

To handle the message within the onMessage() method (for example, to pass the message on to another enterprise bean), you use standard JMS. (This is known as bean-managed messaging.)
If you are using a JCA-compliant Resource Adapter with a different message listener interface, another method besides onMessage() may be needed. For information about the message listener interface needed, see the documentation that was provided with your JCA Resource Adapter.

ejbCreate()
You must define and implement an ejbCreate method for each way in which you want a new instance of an enterprise bean to be created.

ejbRemove()
This method is invoked by the container when a client invokes the remove method inherited by the enterprise bean's home interface from the javax.ejb.EJBHome interface. This method must contain any code to execute before an enterprise bean instance is removed from the container (and the associated data is removed from the data source).

ejbTimeout(Timer)
This method is needed only to support notifications from the timer service, and contains the business logic that handles time events received.

For example, the following code extract shows how to access the text and the JMS MessageID, from a JMS message of type TextMessage:Figure 1. Code example: The onMessage() method of a message bean. This figure shows a code extract for a basic onMessage() method of a sample message-driven bean. The method unpacks the incoming text message to extract the text and message identifier and calls a private putMessage method (defined within the same message bean class) to put the message onto another queue.
 public void onMessage(javax.jms.Message msg)
{
        String text      = null;
        String messageID = null;

        try
        {
                text = ((TextMessage)msg).getText();

                System.out.println("senderBean.onMessage(), msg text2: "+text);

                //
                // store the message id to use as the Correlator value
                //
                messageID = msg.getJMSMessageID();

                // Call a private method to put the message onto another queue
                putMessage(messageID, text);
        }
        catch  (Exception err)
        {
                err.printStackTrace();
        }
        return;
}
The result of this step is a message-driven bean that can be assembled into an EAR file for deployment.
Optional: Use the EJB deployment descriptor editor to review and, if needed, change the deployment properties. You can use the EJB deployment descriptor editor to review deployment properties specified on the EJB Creation Wizard (like Transaction type and Message selector) and other default deployment properties.
If needed, you can override the values of these properties later, after the enterprise application has been exported into an EAR file for deployment.
In the property pane, select the Beans tab.

Specify general deployment properties.

Transaction type

Whether the message bean manages its own transactions or the container manages transactions on behalf of the bean.

Bean

The message bean manages its own transactions

Container

The container manages transactions on behalf of the bean
Specify advanced deployment properties.
Under Activation Configuration, review the following properties:
Acknowledge mode

How the session acknowledges any messages it receives.
This property applies only to message-driven beans that uses bean-managed transaction demarcation (Transaction type is set to Bean).

Auto Acknowledge

The session automatically acknowledges a message when it has either successfully returned from a call to receive, or the message listener it has called to process the message successfully returns.

Dups OK Acknowledge

The session lazily acknowledges the delivery of messages. This is likely to result in the delivery of some duplicate messages if JMS fails, so it should be used only by consumers that are tolerant of duplicate messages.

As defined in the EJB specification, clients cannot use using Message.acknowledge() to acknowledge messages. If a value of CLIENT_ACKNOWLEDGE is passed on the createxxxSession call, then messages are automatically acknowledged by the appserver and Message.acknowledge() is not used.

Destination type

Whether the message bean uses a queue or topic destination.

Queue

The message bean uses a queue destination.

Topic

The message bean uses a topic destination.

Durability

Whether a JMS topic subscription is durable or non-durable.

Durable

A subscriber registers a durable subscription with a unique identity that is retained by JMS. Subsequent subscriber objects with the same identity resume the subscription in the state it was left in by the earlier subscriber. If there is no active subscriber for a durable subscription, JMS retains the subscription's messages until they are received by the subscription or until they expire.

Nondurable

Non-durable subscriptions last for the lifetime of their subscriber object. This means that a client sees the messages published on a topic only while its subscriber is active. If the subscriber is not active, the client is missing messages published on its topic.
A non-durable subscriber can only be used in the same transactional context (for example, a global transaction or an unspecified transaction context) that existed when the subscriber was created. For more information about this context restriction, see The effect of transaction context on non-durable subscribers.

Message selector
The JMS message selector to be used to determine which messages the message bean receives; for example:
JMSType='car' AND color='blue' AND weight>2500
The selector string can refer to fields in the JMS message header and fields in the message properties. Message selectors cannot reference message body values.
For more details about these properties, see Message-driven bean deployment descriptor properties.
Specify bindings deployment properties.
Under WebSphere Bindings, select the JCA Adapter option then specify the bindings deployment properties:

ActivationSpec JNDI name

Type the JNDI name of the J2C activation specification that is to be used to deploy this message-driven bean. This name must match the name of a J2C activation specification that you define to WAS.

ActivationSpec Authorization Alias

The name of a J2C authentication alias used for authentication of connections to the JCA resource adapter. A J2C authentication alias specifies the user ID and password that is used to authenticate the creation of a new connection to the JCA resource adapter.

Destination JNDI name

Type the JNDI name that the message-driven bean uses to look up the JMS destination in the JNDI name space.
Assemble and package the application for deployment.
Results
The result of this task is an EAR file, containing the message-driven bean, for the enterprise application that can be deployed in WebSphere Application Server.

What to do next
After you have developed an enterprise application to use message-driven beans, configure and deploy the application; for example, define J2C activation specifications for the message-driven beans and, optionally, change the deployment descriptor attributes for the application. For more information about configuring and deploying an application that uses message-driven beans, see Deploying an enterprise application to use message-driven beans

Message-driven bean deployment descriptor properties

Related tasks

Deploying an enterprise application to use message-driven beans against JCA 1.5-compliant resources
Programming to use message-driven beans