| <div class="wiki-content maincontent"><h3 id="HowdoesaQueuecomparetoaTopic-Topics">Topics</h3> |
| <p>In JMS a Topic implements <em>publish and subscribe</em> semantics. When you publish a message it goes to all the subscribers who are interested - so zero to many subscribers will receive a copy of the message. Only subscribers who had an active subscription at the time the broker receives the message will get a copy of the message.</p> |
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| <h3 id="HowdoesaQueuecomparetoaTopic-Queues">Queues</h3> |
| <p>A JMS Queue implements <em>load balancer</em> semantics. A single message will be received by exactly one consumer. If there are no consumers available at the time the message is sent it will be kept until a consumer is available that can process the message. If a consumer receives a message and does not acknowledge it before closing then the message will be redelivered to another consumer. A queue can have many consumers with messages <em>load balanced</em> across the available consumers.</p> |
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| <p>So Queues implement a reliable load balancer in JMS.</p></div> |
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