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< title > ActiveMQ Delayed Redelivery Example< / title >
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< h1 > Delayed Redelivery Example< / h1 >
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< p > This example demonstrates how ActiveMQ can be configured to provide a delayed redelivery in the case
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where a message needs to be redelivered.< / p >
< p > Delaying redelivery can often be useful in the case that clients regularly fail or roll-back. Without a delayed
redelivery, the system can get into a "thrashing" state, with delivery being attempted, the client rolling back, and
delivery being re-attempted ad infinitum in quick succession, using up valuable CPU and network resources.< / p >
< p > Re-delivery occurs when the session is closed with unacknowledged messages. The unacknowledged messages will
be redelivered.< / p >
< p > By providing a redelivery delay, it can be specified that a delay of, say, 10 seconds is implemented between rollback
and redelivery. The specific delay is configurable on both a global and per destination level, by using wild-card
matching on the address settings.< / p >
< h2 > Example setup< / h2 >
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< p > Redelivery delay is specified in the configuration file < a href = "src/main/resources/activemq/server0/activemq-configuration.xml" > activemq-configuration.xml< / a > :< / p >
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< p > In this example we set the redelivery delay to 5 seconds for the specific example queue. We could set redelivery delay on
on multiple queues by specifying a wild-card in the match, e.g. < code > match="jms.#"< / code > would apply the settings
to all JMS queues and topics.< / p >
< p > We then consume a message in a transacted session, and rollback, and note that the message is not redelivered until
after 5 seconds.< / p >
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< code > < address-setting match="jms.queue.exampleQueue">
< redelivery-delay> 5000< /redelivery-delay>
< /address-setting>
< / code >
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< p > < i > To run the example, simply type < code > mvn verify< / code > from this directory< / i > < / p >
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< li > Create an initial context to perform the JNDI lookup.< / li >
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< code > initialContext = getContext(0);< / code >
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< li > Perform a lookup on the queue< / li >
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< code > Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");< / code >
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< li > Perform a lookup on the Connection Factory< / li >
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< code > ConnectionFactory cf = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");< / code >
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< li > Create a JMS Connection< / li >
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< code > connection = cf.createConnection();< / code >
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< li > Create a transacted JMS Session
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< code > Session session = connection.createSession(true, 0);< / code >
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< li > Create a JMS Message Producer< / li >
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< code > MessageProducer producer = session.createProducer(queue);< / code >
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< li > Create a Text Message< / li >
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< code > TextMessage message = session.createTextMessage("this is a text message");< / code >
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< li > Send the Message< / li >
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< code > producer.send(message);< / code >
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< li > We commit the session to effectively send the message to the queue< / li >
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< code > session.commit();< / code >
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< li > We create a JMS message consumer on the queue< / li >
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< code > MessageConsumer messageConsumer = session.createConsumer(queue);< / code >
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< li > We start the connection. In order for delivery to occur on any consumers or subscribers on a connection, the connection must be started< / li >
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< code > connection.start();< / code >
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< li > We receive the message...< / li >
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< code > TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
System.out.println("1st delivery from " + queue.getQueueName() + ": " + messageReceived.getText());< / code >
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< li > ...but we roll back the session. the message returns to the queue, but only after a
5 second delay< / li >
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< code > session.rollback();< / code >
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< li > We try to receive the message but it's being delayed< / li >
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< code >
messageReceived = (TextMessage)messageConsumer.receive(3000);
if (messageReceived != null)
{
return false;
}
System.out.println("Redelivery has been delayed so received message is " + messageReceived);
< / code >
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< li > We try and receive the message again, this time we should get it< / li >
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< code >
messageReceived = (TextMessage)messageConsumer.receive(3000);
System.out.println("2nd delivery from " + queue.getQueueName() + ": " + messageReceived.getText());
< / code >
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< li > We rollback the session again to cause another redelivery, and we time how long this one takes< / code >
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long start = System.currentTimeMillis();
session.rollback();
messageReceived = (TextMessage)messageConsumer.receive(8000);
long end = System.currentTimeMillis();
System.out.println("3nd delivery from " + queue.getQueueName() + ": " + messageReceived.getText() +
" after " + (end - start) + " milliseconds.");
< / code >
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< li > And finally, < b > always< / b > remember to close your JMS connections and resources after use, in a < code > finally< / code > block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects< / li >
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< code > finally
{
if (initialContext != null)
{
initialContext.close();
}
if (connection != null)
{
connection.close();
}
}< / code >
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< h2 > More information< / h2 >
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< li > User Manual's < a href = "../../../docs/user-manual/en/html_single/index.html#undelivered-messages" > Undelivered Messages chapter< / a > < / li >
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