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The traditional message model, where a message is sent to a queue and later removed by a single receiver, is called point-to-point messaging. In addition to this familiar model, JMS also supports the publish-and-subscribe messaging model. Here, messages are published to topics, rather than sent to queues. Interested receivers subscribe to individual topics and receive a copy of each message published to the topic. To subscribe, a subscriber registers with the topic, providing a unique identifier.
JMS queues and topics are identified by their JNDI names. A JNDI naming service is required to use the JMS Transport. The JNDI naming service contains entries for the desired JMS queues (implementers of javax.jms.Queue) and topics (implementers of javax.jms.Topic) as well as the necessary JMS connection factories (implementers of either javax.jms.QueueFactory or javax.jms.Topic).
All methods that receive messages automatically time out if no message is available. The timeout length is three seconds by default and can be specified by the ReceiveTimeout argument. A value of zero for this argument disables the timeout, causing the method to wait indefinitely for a message to arrive. Whether a call to Receive or Subscribe timed out is provided as the TimedOut property of the output property set.
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