Message listeners

WebSphere MQ Everyplace allows an application to listen for events occurring on queues. The application is able to specify message filters to identify the messages in which it is interested. A message arriving on queue triggers an event.

The Application example Ex 4 contains an example of using message listeners.

To enable this, an MQeMessageListener object must be created. The new() function for this takes an extra parameter, which is a function pointer. This function pointer indicates the function that should be called when a message arrives on the queue. This function should have the prototype:

- MQEVOID messageArrived(MQeMessageEventHndl hE);

Where MQeMessageEventHndl is a handle to an object that contains information about the message that has arrived. The queue needs to be aware of this handle , so the mqeQueueManager_addMessageListener function must be called with the MQeMessageListener object handle.

The MQeMessageEvent contains information about the message including:

Message filters only work on local queues. A separate technique known as message polling allows messages to be obtained as soon as they arrive on remote queues. (This is discussed in the next section.)



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