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21.2.3. Receiving messages using a message-driven bean

You can process messages with any EJB3 message-driven bean. Message-driven beans can sometimes be Seam components, in which case, you can inject other event- and application-scoped Seam components. The following is an example of the payment receiver, which delegates to the payment processor.

Note

You may need to set the create attribute on the @In annotation to true so that Seam can create an instance of the component to be injected. (This is necessary only if the component does not support auto-creation — that is, it is not annotated with @Autocreate.)
First, create a message-driven bean to receive the message: 
@MessageDriven(activationConfig = 
    {@ActivationConfigProperty(propertyName = "destinationType",
                               propertyValue = "javax.jms.Queue"),
     @ActivationConfigProperty(propertyName = "destination",
                               propertyValue = "queue/paymentQueue")
})

@Name("paymentReceiver")
public class PaymentReceiver implements MessageListener
{
  @Logger private Log log;

  @In(create = true) private PaymentProcessor paymentProcessor;
    
  @Override
  public void onMessage(Message message)
  {
    try {
      paymentProcessor.processPayment((Payment) ((ObjectMessage) 
                                      message).getObject());
    } catch (JMSException ex) {
      log.error("Message payload did not contain a Payment object", ex);
    } 
  }
}
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Next, implement the Seam component to which the receiver will delegate payment processing: 
@Name("paymentProcessor")
public class PaymentProcessor {
  @In private EntityManager entityManager;

  public void processPayment(Payment payment) {
    // perhaps do something more fancy
    entityManager.persist(payment);
  }
}
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If you want to perform transaction operations in your message-driven bean, ensure that you are working with an XA datasource, or you will not be able to roll back database changes in the event that a database transaction commits, but a subsequent message operation fails.
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