I'm starting a JEE project that needs to be strongly scalable. So far, the concept was:

• several Message Driven Beans, responsible for different parts of the architecture
• each MDB has a Session Bean injected, handling the business logic
• a couple of Entity Beans, providing access to the persistence layer
• communication between the different parts of the architecture via Request/Reply concept via JMS messages:
  • MDB receives msg containing activity request
  • uses its session bean to execute necessary business logic
  • returns response object in msg to original requester

The idea was that by de-coupling parts of the architecture from each other via the message bus, there is no limit to the scalability. Simply start more components - as long as they are connected to the same bus, we can grow and grow.

Unfortunately, we're having massive problems with the request-reply concept. Transaction Mgmt seems to be in our way plenty. It seams that session beans are not supposed to consume messages?!

Reading http://blogs.sun.com/fkieviet/entry/request_reply_from_an_ejb and http://forums.sun.com/message.jspa?messageID=10338789, I get the feeling that people actually recommend against the request/reply concept for EJBs.

If that is the case, how do you communicate between your EJBs? (Remember, scalability is what I'm after)

Details of my current setup:

• MDB 1 'TestController', uses (local) SLSB 1 'TestService' for business logic
• TestController.onMessage() makes TestService send a message to queue XYZ and requests a reply
  • TestService uses Bean Managed Transactions
  • TestService establishes a connection & session to the JMS broker via a joint connection factory upon initialization (@PostConstruct)
  • TestService commits the transaction after sending, then begins another transaction and waits 10 sec for the response
• Message gets to MDB 2 'LocationController', which uses (local) SLSB 2 'LocationService' for business logic
• LocationController.onMessage() makes LocationService send a message back to the requested JMSReplyTo queue
  • Same BMT concept, same @PostConstruct concept
• all use the same connection factory to access the broker

Problem: The first message gets send (by SLSB 1) and received (by MDB 2) ok. The sending of the returning message (by SLSB 2) is fine as well. However, SLSB 1 never receives anything - it just times out.

I tried without the messageSelector, no change, still no receiving message.

Is it not ok to consume message by a session bean?

SLSB 1 - TestService.java

@Resource(name = "jms/mvs.MVSControllerFactory")
private javax.jms.ConnectionFactory connectionFactory;

@PostConstruct
public void initialize() {
    try {
      jmsConnection = connectionFactory.createConnection();
      session = jmsConnection.createSession(false, Session.AUTO_ACKNOWLEDGE);
      System.out.println("Connection to JMS Provider established");
    } catch (Exception e) { }
}

public Serializable sendMessageWithResponse(Destination reqDest, Destination respDest, Serializable request) {
    Serializable response = null;

    try {
        utx.begin();
        Random rand = new Random();
        String correlationId = rand.nextLong() + "-" + (new Date()).getTime();

        // prepare the sending message object
        ObjectMessage reqMsg = session.createObjectMessage();
        reqMsg.setObject(request);
        reqMsg.setJMSReplyTo(respDest);
        reqMsg.setJMSCorrelationID(correlationId);

        // prepare the publishers and subscribers
        MessageProducer producer = session.createProducer(reqDest);

        // send the message
        producer.send(reqMsg);
        System.out.println("Request Message has been sent!");
        utx.commit();

        // need to start second transaction, otherwise the first msg never gets sent
        utx.begin();
        MessageConsumer consumer = session.createConsumer(respDest, "JMSCorrelationID = '" + correlationId + "'");
        jmsConnection.start();
        ObjectMessage respMsg = (ObjectMessage) consumer.receive(10000L);
        utx.commit();

        if (respMsg != null) {
            response = respMsg.getObject();
            System.out.println("Response Message has been received!");
        } else {
            // timeout waiting for response
            System.out.println("Timeout waiting for response!");
        }

    } catch (Exception e) { }

    return response;
}

SLSB 2 - LocationService.Java (only the reply method, rest is same as above)

public boolean reply(Message origMsg, Serializable o) {
    boolean rc = false;

    try {
        // check if we have necessary correlationID and replyTo destination
        if (!origMsg.getJMSCorrelationID().equals("") && (origMsg.getJMSReplyTo() != null)) {
            // prepare the payload
            utx.begin();
            ObjectMessage msg = session.createObjectMessage();
            msg.setObject(o);

            // make it a response
            msg.setJMSCorrelationID(origMsg.getJMSCorrelationID());
            Destination dest = origMsg.getJMSReplyTo();

            // send it
            MessageProducer producer = session.createProducer(dest);
            producer.send(msg);
            producer.close();
            System.out.println("Reply Message has been sent");
            utx.commit();

            rc = true;
        }

    } catch (Exception e) {}

    return rc;
}

sun-resources.xml

<admin-object-resource enabled="true" jndi-name="jms/mvs.LocationControllerRequest"  res-type="javax.jms.Queue"  res-adapter="jmsra">
    <property name="Name" value="mvs.LocationControllerRequestQueue"/>
</admin-object-resource>
<admin-object-resource enabled="true" jndi-name="jms/mvs.LocationControllerResponse"  res-type="javax.jms.Queue"  res-adapter="jmsra">
    <property name="Name" value="mvs.LocationControllerResponseQueue"/>
</admin-object-resource>

<connector-connection-pool name="jms/mvs.MVSControllerFactoryPool"  connection-definition-name="javax.jms.QueueConnectionFactory"  resource-adapter-name="jmsra"/>
<connector-resource enabled="true" jndi-name="jms/mvs.MVSControllerFactory" pool-name="jms/mvs.MVSControllerFactoryPool"  />