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Marcus Janke
Marcus Janke

Dec 27, 2019
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2 min read
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Consuming segmented IBM MQ messages in Java

Ever got frustrated about IBM’s MQ message segmentation feature on the consumer's end? I had this feeling a couple of years ago when consuming a queue from an external provider that segmented large messages of batch data. This should spare you some pain.
Photo by davide ragusa on Unsplash

I found it extremely annoying and cumbersome to find suitable client options to make this work. In fact, I had the feeling that everyone was looking for the answer but no one had been successful. So I had to pick up bits and pieces all over the internet and finally made this work. So here’s what you need to do:

    Set up your environment:

MQEnvironment.hostname = host;  
MQEnvironment.port = port;  
MQEnvironment.channel = channel;

2. Create your QueueManager instance:

MQQueueManager manager = new MQQueueManager("queueManagerName");

3. Access your MQQueue with the correct open options:

int openOptions = MQC.MQOO_INPUT_SHARED 
    | MQC.MQOO_INQUIRE 
    | MQC.MQOO_FAIL_IF_QUIESCING;
MQQueue queue = manager.accessQueue(queueName, openOptions);

    MQOO_INPUT_SHARED: Allow shared access to your queue.
    MQOO_INQUIRE: Allow inquiring queue attributes.
    MQOO_FAIL_IF_QUIESCING: Checks quiescing state of queue on open.

4. Set up the MQGetMessageOptions:

MQGetMessageOptions gmo = new MQGetMessageOptions();
gmo.options = MQC.MQGMO_ALL_SEGMENTS_AVAILABLE 
    | MQC.MQGMO_SYNCPOINT 
    | MQC.MQGMO_COMPLETE_MSG;  
gmo.matchOptions = MQC.MQMO_NONE;  
gmo.waitInterval = 10000;

    MQGMO_ALL_SEGMENTS_AVAILABLE:

    Segments in a logical message become available for retrieval only when all segments in the logical message are available.

    MQGMO_SYNCPOINT:

    The message is marked as being unavailable to other applications, but it is deleted from the queue only when the unit of work is committed. The message is made available again if the unit of work is backed out.

    MQGMO_COMPLETE_MSG:

    Only a complete logical message can be returned by the MQGET call. If the logical message is segmented, the queue manager reassembles the segments and returns the complete logical message to the application; the fact that the logical message was segmented is not apparent to the application retrieving it.

5. Get your MQMessage:

MQMessage message = new MQMessage();   
queue.get(message, gmo);// Do your stuff with the messagemessage.clearMessage();
queue.close(); 
manager.disconnect();

The main point is to get the GetMessageOptions right. And that’s basically it.

I reckon that reading this might probably raise lots of questions about why the MQ client library is written in this unusual way. I did so, too. And I did not find any suitable answer. You got just to cope with this and encapsulate access as best as possible. ;)

Disclaimer: I am perfectly aware that this solution might be totally outdated. I just felt the urge to finally get this off my mind ;) Feel free to comment.

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