Question

I am using the Spring DefaultMessageListenerContainer to gain some dynamic benefits in setting the MessageSelector value since I am using the Glassfish OpenMQ which is not that advanced in that regards.
Let’s have a JMS message. The listener issues a specific failure that means: retry after x seconds. It tries again with failure: retry after x*y seconds, and so on the time grows exponentially. If you cannot handle it after z retries, consider it as a poison JMS message.

DefaultMessageListenerContainer dmlc;
dmlc.stop();
dmlc.setMessageSelector(String.format("retries < %d AND retryTime <= %d", z, System.currentTimeMillis()));
dmlc.start();

I am not that satisfied with this solution, especially, when the Spring docs raise warning here:-). However, for the moment things meet our needs.

Now, I have a number of EJBs message consumers on different applications. Some of them need such dynamic changes of the messageSelector. Unfortunately, and to-my-best-knowledge, EJB MDBs do not support such dynamic “features”. For example, see this.

Is that correct? is there a workaround for an EJB solution? I would appreciate any help.

Answer 1

To achieve dynamic changes to the message selector, you’d need to implement it straight in JMS, e.g.

ConnectionFactory cf;
Connection connection = cf.createConnection();
session = connection.createSession(transactional, acknowledgeMode);

MessageConsumer messageConsumer = session.createConsumer(destination, "message selector");

Additionally, you’d need to place this code some place it executes on its own, perhaps in an asynchronous task? But you’d be reinventing the wheel, as Spring DMLC does that better.

I don’t know why you’re doing this:

• for load balancing? The message broker should take care of this.
• for handling temporary downtimes? The queue should be configured to be able to store appropriate number of messages, or switch delivery to other node in cluster.