Advanced Queuing - Oracle

JMS Message Consumer Features
AQ Exception Handling
}
tsubs[3] = jms_session.createDurableSubscriber(topic[3], "SHIPPED_ORDER");
MessageListener mL = new CustomerListener(jms_session);
/* set the session’s message listener */
jms_session.setMessageListener(mL);
}catch(JMSException ex)
{ System.out.println("Exception: " + ex); }
AQ provides four integrated mechanisms to support exception handling in
applications: EXCEPTION_QUEUES, EXPIRATION, MAX_RETRIES and RETRY_
DELAY.
An exception_queue is a repository for all expired or unserviceable messages.
Applications cannot directly enqueue into exception queues. However, an
application that intends to handle these expired or unserviceable messages can
receive/remove them from the exception queue.
To retrieve messages from exception queues, the JMS client must use the
point-to-point interface.The exception queue for messages intended for a topic must
be created in a queue table with multiple consumers enabled. Like any other queue,
the exception queue must be enabled for receiving messages using the start method
in the AQOracleQueue class. You will get an exception if you try to enable it for
enqueue.
The exception queue is a provider (Oracle) specific message property called "JMS_
OracleExcpQ" that can be set with the message before sending/publishing it. If an
exception queue is not specified, the default exception queue is used. If the
queue/topic is created in a queue table, say QTAB, the default exception queue will
be called AQ$_QTAB_E. The default exception queue is automatically created when
the queue table is created.
Messages are moved to the exception queues by AQ under the following
conditions:
The message is not being dequeued within the specified timeToLive. For
messages intended for more than one subscriber, the message will be moved to
the exception queue if one or more of the intended recipients is not able to
dequeue the message within the specified timeToLive. If the timeToLive
was not specified for the message, (either in the publish or send call, or as the
publisher or sender), it will never expire.
12-80 Oracle9i Application Developer’s Guide - Advanced Queuing