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<title>ActiveMQ Artemis Dead Letter Example</title>
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<h1>Dead Letter Example</h1>
<pre>To run the example, simply type <b>mvn verify</b> from this directory, <br>or <b>mvn -PnoServer verify</b> if you want to start and create the server manually.</pre>
<p>This example shows you how to define and deal with dead letter messages.</p>
<p>Messages can be delivered unsuccessfully (e.g. if the transacted session used to consume them is rolled back).
Such a message goes back to the JMS destination ready to be redelivered.
However, this means it is possible for a message to be delivered again and again without any success and remain in the destination, clogging the system.</p>
<p>To prevent this, messaging systems define dead letter messages: after a specified unsuccessful delivery attempts, the message is removed from the destination
and instead routed to a <em>dead letter address</em> where they can be consumed for further investigation.
<p>
The example will show how to configure ActiveMQ Artemis to route a message to a dead letter address after 3 unsuccessful delivery attempts.<br />
The example will send 1 message to a queue. We will deliver the message 3 times and rollback the session every time.<br />
On the 4th attempt, there won't be any message to consume: it will have been moved to a <em>dead letter address</em>.<br />
We will then consume this dead letter message.
</p>
<h2>Example setup</h2>
<p><em>Dead letter addresses</em> and <em>maximum delivery attempts</em> are defined in the configuration file <a href="src/main/resources/activemq/server0/broker.xml">broker.xml</a>:</p>
<pre class="prettyprint">
<code><address-setting match="jms.queue.exampleQueue">
<dead-letter-address>jms.queue.deadLetterQueue</dead-letter-address>
<max-delivery-attempts>3</max-delivery-attempts>
</address-setting>
</code>
</pre>
<p>This configuration will moved dead letter messages from <code>exampleQueue</code> to the <code>deadLetterQueue</code>.</p>
<p>ActiveMQ Artemis allows to specify either a <code>Queue</code> by prefixing the <code>dead-letter-address</code> with <code>jms.queue.</code>
or a <code>Topic</code> by prefixing with <code>jms.topic.</code>.<br />
In this example, we will use a <code>Queue</code> to hold the dead letter messages.</p>
<p>The maximum attempts of delivery is <code>3</code>. Once this figure is reached, a message is considered a dead letter message and is moved to
the <code>deadLetterQueue</code>.
<p>Since we want to consume messages from this deadLetterQueue, we also need to add a JNDI binding to perform a lookup.
This is configured in <a href="src/main/resources/activemq/server0/activemq-jms.xml">activemq-jms.xml</a></p>
<pre class="prettyprint">
<code><queue name="deadLetterQueue">
<entry name="/queue/deadLetterQueue"/>
</queue></code>
</pre>
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