How the postcards get there

 

When other instances of Postcard on this computer use the same queue manager and queue, the messages are being put and got from the one queue. This does, however, verify that the WebSphere MQ code installed on this computer is configured and working correctly.

JMS Postcard can only send to another queue manager if a connection to that queue manager exists. This connection exists because either both queue managers are members of the same cluster, or you have explicitly created a connection yourself. JMS Postcard can therefore assume that it can connect to the queue manager, and connects to it, opens the queue, and puts a message, as already described, leaving all the work of getting the message there to the WebSphere MQ cluster code. In other words, JMS Postcard uses only one piece of code for putting the message, and does not need to know whether the message is going to another computer.

In JMS Postcard, when session.createSender('postcard') is called, the cluster code checks the repository to find the other queue manager, and to check that the queue exists, and throws an exception if this was not possible for any reason.

When queueSender.send(theMessage) is called, the cluster code opens a channel to the other queue manager (creating it if necessary) and sends the message.

Discard the channel afterwards, if the cluster optimizing code does not need it. If the queue managers are on different computers, that is all handled by the cluster code.

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