Running Message Driven Beans

Source:8.2. Topic Message Driven Bean Example

OCP JavaEE 6 EJB Developer Study Notes by Ivan A Krizsan Version: April 8, 2012

On Running the example and issuing a request to the following URL thrice:

http://localhost:8080/TopicMessageDrivenExample/sendmsg.do

The following output was seen in the server.logs:

INFO: *** MessageProducerServlet created

INFO: *** TopicListenerEJB created: 1
INFO: *** TopicListenerEJB created: 2
INFO: *** TopicListenerEJB created: 3
INFO: *** Bean 3 received message: com.sun.messaging.jms.ra.DirectObjectPacket@1a4f723
INFO: *** Bean 2 received message: com.sun.messaging.jms.ra.DirectObjectPacket@14a40bd
INFO: *** Bean 1 received message: com.sun.messaging.jms.ra.DirectObjectPacket@15d3137
INFO: Received message with number: 1
INFO:  Message string: Hello Message Driven Beans
INFO: Received message with number: 1
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:32:14 IST 2013
INFO: Received message with number: 1
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:32:14 IST 2013
INFO:  Message time: Sat Feb 16 21:32:14 IST 2013

INFO: *** Bean 2 received message: com.sun.messaging.jms.ra.DirectObjectPacket@447465
INFO: Received message with number: 2
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:32:41 IST 2013
INFO: *** Bean 1 received message: com.sun.messaging.jms.ra.DirectObjectPacket@c3af8c
INFO: Received message with number: 2
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:32:41 IST 2013
INFO: *** Bean 3 received message: com.sun.messaging.jms.ra.DirectObjectPacket@1a41a8d
INFO: Received message with number: 2
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:32:41 IST 2013

INFO: *** Bean 2 received message: com.sun.messaging.jms.ra.DirectObjectPacket@153488e
INFO: Received message with number: 3
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:33:03 IST 2013
INFO: *** Bean 3 received message: com.sun.messaging.jms.ra.DirectObjectPacket@4aaf0d
INFO: Received message with number: 3
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:33:03 IST 2013
INFO: *** Bean 1 received message: com.sun.messaging.jms.ra.DirectObjectPacket@1ad5432
INFO: Received message with number: 3
INFO:  Message string: Hello Message Driven Beans
INFO:  Message time: Sat Feb 16 21:33:03 IST 2013

Question: Why is there no order of messages received by MDB,each request results in a different MDB to receive a message( not in order they were created) ?

Please advise.

Mohit,
Messages may be delivered out of sequence , EJB specs does not gurantee message delivery order.

See Section 5.4.11 of ejb 3.1 spec.

A container allows many instances of a message-driven bean class to be executing concurrently, thus allowing for the concurrent processing of a stream of messages. No guarantees are made as to the exact order in which messages are delivered to the instances of the message-driven bean class, although the container should attempt to deliver messages in order when it does not impair the concurrency of message processing. Message-driven beans should therefore be prepared to handle messages that are out of sequence: for example, the message to cancel a reservation may be delivered before the message to make the reservation.

Hope this helps.

Thanks Ravi
However,The example above sends only one message when i issue a request using URL.

My Question is why the order in which beans were created ( i.e. 1,2,3) are not getting the message in the same order ?

The order of message receivable is opposite of Bean creation
Each of the three message driven beans receive a copy of the message sent to the topic

Mohit,

Order of bean creation is not tied to order in which they recieve the messages
MDB very much works like stateless session beans , where in container creates pool of MDB instances once the bean is deployed.
once we have a pool , Container can pick any instance from the pool and delegate it to process the message. Order is not supposed to be preserved.

Thanks Ravi