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<h1>Delayed Redelivery Example</h1>
<p>This example demonstrates how HornetQ can be configured to provide a delayed redelivery in the case
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>
<p>Redelivery delay is specified in the configuration file <a href="src/main/resources/hornetq/server0/hornetq-configuration.xml">hornetq-configuration.xml</a>:</p>
<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>
<pre class="prettyprint">
<code><address-setting match="jms.queue.exampleQueue">
<redelivery-delay>5000</redelivery-delay>
</address-setting>
</code>
</pre>
<p><i>To run the example, simply type <code>mvn verify</code> from this directory</i></p>
<ol>
<li>Create an initial context to perform the JNDI lookup.</li>
<pre class="prettyprint">
<code>initialContext = getContext(0);</code>
</pre>
<li>Perform a lookup on the queue</li>
<pre class="prettyprint">
<code>Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");</code>
</pre>
<li>Perform a lookup on the Connection Factory</li>
<pre class="prettyprint">
<code>ConnectionFactory cf = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");</code>
</pre>
<li>Create a JMS Connection</li>
<pre class="prettyprint">
<code>connection = cf.createConnection();</code>
</pre>
<li>Create a transacted JMS Session
<pre class="prettyprint">
<code>Session session = connection.createSession(true, 0);</code>
</pre>
<li>Create a JMS Message Producer</li>
<pre class="prettyprint">
<code>MessageProducer producer = session.createProducer(queue);</code>
</pre>
<li>Create a Text Message</li>
<pre class="prettyprint">
<code>TextMessage message = session.createTextMessage("this is a text message");</code>
</pre>
<li>Send the Message</li>
<pre class="prettyprint">
<code>producer.send(message);</code>
</pre>
<li>We commit the session to effectively send the message to the queue</li>
<pre class="prettyprint">
<code>session.commit();</code>
</pre>
<li>We create a JMS message consumer on the queue</li>
<pre class="prettyprint">
<code>MessageConsumer messageConsumer = session.createConsumer(queue);</code>
</pre>
<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>
<pre class="prettyprint">
<code>connection.start();</code>
</pre>
<li>We receive the message...</li>
<pre class="prettyprint">
<code>TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
System.out.println("1st delivery from " + queue.getQueueName() + ": " + messageReceived.getText());</code>
</pre>
<li>...but we roll back the session. the message returns to the queue, but only after a
5 second delay</li>
<pre class="prettyprint">
<code>session.rollback();</code>
</pre>
<li>We try to receive the message but it's being delayed</li>
<pre class="prettyprint">
<code>
messageReceived = (TextMessage)messageConsumer.receive(3000);
if (messageReceived != null)
{
return false;
}
System.out.println("Redelivery has been delayed so received message is " + messageReceived);
</code>
</pre>
<li>We try and receive the message again, this time we should get it</li>
<pre class="prettyprint">
<code>
messageReceived = (TextMessage)messageConsumer.receive(3000);
System.out.println("2nd delivery from " + queue.getQueueName() + ": " + messageReceived.getText());
</code>
</pre>
<li>We rollback the session again to cause another redelivery, and we time how long this one takes</code>
<pre class="prettyprint">
<code>
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>
</pre>
<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>
<pre class="prettyprint">
<code>finally
{
if (initialContext != null)
{
initialContext.close();
}
if (connection != null)
{
connection.close();
}
}</code>
</pre>
</ol>
<h2>More information</h2>
<ul>
<li>User Manual's <a href="../../../docs/user-manual/en/html_single/index.html#undelivered-messages">Undelivered Messages chapter</a></li>
</ul>
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