Message-driven beans - automatic message retrieval
WAS supports the use of message-driven beans as asynchronous message consumers.
Messaging with message-driven beans is shown in the figureMessaging with message-driven beans.
A client sends messages to the destination (or endpoint) for which the message-driven bean is deployed as the message listener. When a message arrives at the destination, the EJB container invokes the message-driven bean automatically without an application having to explicitly poll the destination. The message-driven bean implements some business logic to process incoming messages on the destination.
Message-driven beans can be configured as listeners on a Java Connector Architecture (JCA) 1.5 resource adapter or against a listener port (as in WAS V5). With a JCA 1.5 resource adapter, message-driven beans can handle generic message types, not just JMS messages. This makes message-driven beans suitable for handling generic requests inbound to WAS from enterprise information systems through the resource adapter. In the JCA 1.5 specification, such message-driven beans are commonly called message endpoints or simply endpoints.
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.
A message driven bean can be registered with the EJB timer service for time-based event notifications if it implements the javax.ejb.TimedObject interface in addition to the message listener interface.
You are recommended to develop a 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.
Messages arriving at a destination being processed by a message-driven bean have no client credentials associated with them; the messages are anonymous. Security depends on the role specified by the RunAs Identity for the message-driven bean as an EJB component. For more information about EJB security, see Securing enterprise bean applications.
For JMS messaging, message-driven beans can use a JMS provider that has a JCA 1.5 resource adapter, such as the default messaging provider that is part of WAS V6. With a JCA 1.5 resource adapter, you deploy EJB 2.1 message-driven beans as JCA 1.5-compliant resources, to use a J2C activation specification. If the JMS provider does not have a JCA 1.5 resource adapter, such as the V5 Default Messaging and WebSphere MQ, configure JMS message-driven beans against a listener port (as in WebSphere Application Server V5). Figure 1. Messaging with message-driven beans. This figure shows an incoming message being passed automatically to the onMessage() method of a message-driven bean that is deployed as a listener for the destination. The message-driven bean processes the message, in this case passing the message on to a business logic bean for business processing. For more information, see the text that accompanies this figure.
Sub-topics
Message-driven beans - JCA components
J2C activation specification configuration and use
WAS activation specification optional binding properties
Message-driven beans - transaction support