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);
}
}
}
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);
}
}
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.
