Message Groups in WebSphere MQ

Question

I have a requirement that I need to process JMS Messages (via MDB) in a way that Messages belonging to a certain group (a group ID is set) are consumed by the same bean instance. The behaviour I require in this is that Messages with the same group ID are processed sequentially (though message ordering is irrelevant), and tying them to the same MDB-instance should provide that.

The messages do not carry any kind of sequence number (as it is irrelevant) and we do not know what the first or last message in a group is (there could theoratically "never" be a last message in a group). We want them to be delivered as soon as the consumer is able to receive them.

ActiveMQ provides this exact feature (http://activemq.apache.org/message-groups.html) by simply setting JMSXGroupID. We are bound to WebSphere MQ, though. All I've found out so far is that it is possible to collect Messages of the same group in the queue and using a MessageSelector to receive a "Last Message in Group" Message as described in http://www.ibm.com/developerworks/websphere/library/techarticles/0602_currie/0602_currie.html. We would prefer a cleaner way though (like in ActiveMQ). Does anyone know how to achieve that behaviour in WebSphere?

Thanks!

Answer 1

Generally you use MessageSelectors in IBM product implementations of JMS (both WebSphere MQ and SIBus implementations). These are the equivalent of a filter that would scan the header of an HTTP or SOAP message for web-based protocols.

Though it may not be what you want, it actually is a clean and well thought through design.

However, if you do not want to use MessageSelectors, you will probably have to build your own and "process" a message with a fronting MDB that scans the headers, and then forwards the message to an appropriate queue, where only the MDB that cares about the grouped messages will process them (sort of a gateway/message selector pattern).

If you are using the "pure" JMS API's, then you can ask the Session object to create a MessageConsumer with the specified selector string (value in the header) you want to filter on (again you have to set this yourself).

//assume we have created a JMS Connection and Session object already.
//and looked up the Queue we want already.
MessageConsumer consumerWithSelector = session.createConsumer(queue, groupId);

This is all the pure JMS API's give you. Anything else is purely up to the implementer of the messaging technology, which is then proprietary to their implementation and not portable code.