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POJMS Producer-Consumer-Observer (PCO)
 

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  1. POJMS Producer-Consumer-Observer (PCO)
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    <p>In JMS there are Queues and Topics. As I understand it so far queues are best used for producer/consumer scenarios, where as topics can be used for publish/subscribe. However in my scenario I need a way to combine both approaches and create a producer-consumer-observer architecture.</p> <p>Particularly I have producers which write to some queues and workers, which read from these queues and process the messages in those queues, then write it to a different queue (or topic). Whenever a worker has done a job my GUI should be notified and update its representation of the current system state. Since workers and GUI are different processes I cannot apply a simple observer pattern or notify the GUI directly.</p> <p>What is the best way to realize this using a combination of queues and/or topics? The GUI should always be notified, but it should never consume anything from a queue?</p> <p>I would like to solve this with JMS directly and not use any additional technology such as RMI to implement the observer part.</p> <p>To give a more concrete example:</p> <ol> <li>I have a queue with packages (<code>PACKAGEQUEUE</code>), produced by machine (<code>PackageProducer</code>)</li> <li>I have a worker which takes a package from the <code>PACKAGEQUEUE</code> adds an address and then writes it to a <code>MAILQUEUE</code> (<code>AddressWorker</code>)</li> <li>Another worker processes the <code>MAILQUEUE</code> and sends the packages out by mail (<code>MailWorker</code>).</li> <li>After step 2. when a message is written to the <code>MAILQUEUE</code>, I want to notify the GUI and update the status of the package. Of course the GUI should not consume the messages in the <code>MAILQUEUE</code>, only the <code>MailWorker</code> must consume them.</li> </ol>
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