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<h1>Message Group Example</h1>
<p>This example shows you how to configure and use message groups via a connection factory with HornetQ.</p>
<p>Message groups are sets of messages that has the following characteristics: </p>
<li>Messages in a message group share the same group id, i.e. they have same JMSXGroupID string property values.</li>
<li>Messages in a message group will be all delivered to no more than one of the queue's consumers. The consumer that receives the
first message of a group will receive all the messages that belongs to the group.</li>
<p>You can make any message belong to a message group by setting a 'group-id' on the connection factory. All producers created via this connection factory will set that group id on its messages.
In this example we set the group id 'Group-0'on a connection factory and send messages via 2 different producers and check that only 1 consumer receives them. </p>
<p>Alternatively, HornetQ's connection factories can be configured to <em>auto group</em> messages. By setting <code>autogroup</code> to </code>true</code> on the <code>HornetQConnectionFactory</code>
(or setting <code><autogroup>true</autogroup></code> in <code>hornetq-jms.xml</code>'s connection factory settings), a random unique id
will be picked to create a message group. <em>Every messages</em> sent by a producer created from this connection factory will automatically
be part of this message group.</p>
<h2>Example step-by-step</h2>
<p><i>To run the example, simply type <code>mvn verify</code> from this directory</i></p>
<ol>
<li>First we need to get an initial context so we can look-up the JMS connection factory and destination objects from JNDI. This initial context will get it's properties from the <code>client-jndi.properties</code> file in the directory <code>../common/config</code></li>
<pre class="prettyprint">
<code>InitialContext initialContext = getContext();</code>
</pre>
<li>We look-up the JMS queue object from JNDI</li>
<pre class="prettyprint">
<code>Queue queue = (Queue) initialContext.lookup("/queue/exampleQueue");</code>
</pre>
<li>We look-up the JMS connection factory object from JNDI</li>
<pre class="prettyprint">
<code>ConnectionFactory cf = (ConnectionFactory) initialContext.lookup("/ConnectionFactory");</code>
</pre>
<li>We create a JMS connection</li>
<pre class="prettyprint">
<code>connection = cf.createConnection();</code>
</pre>
<li>We create a JMS session. The session is created as non transacted and will auto acknowledge messages.</li>
<pre class="prettyprint">
<code>Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
</pre>
<li>We create 2 JMS message producers on the session. This will be used to send the messages.</li>
<pre class="prettyprint">
<code>
MessageProducer producer1 = session.createProducer(queue);
MessageProducer producer2 = session.createProducer(queue);</code>
</pre>
<li>We create two consumers.</li>
<pre class="prettyprint">
<code>
MessageConsumer consumer1 = session.createConsumer(queue);
consumer1.setMessageListener(new SimpleMessageListener("consumer-1"));
MessageConsumer consumer2 = session.createConsumer(queue);
consumer2.setMessageListener(new SimpleMessageListener("consumer-2"));
</code>
</pre>
<li>We create and send 10 text messages using each producer</li>
<pre class="prettyprint">
<code>
int msgCount = 10;
for (int i = 0; i < msgCount; i++)
{
TextMessage m = session.createTextMessage("producer1 message " + i);
producer1.send(m);
System.out.println("Sent message: " + m.getText());
TextMessage m2 = session.createTextMessage("producer2 message " + i);
producer2.send(m2);
System.out.println("Sent message: " + m2.getText());
}
</code>
</pre>
<li>We start the connection.</li>
<pre class="prettyprint">
<code>connection.start();</code>
</pre>
<li>We check the group messages are received by only one consumer</li>
<pre class="prettyprint">
<code>
String trueReceiver = messageReceiverMap.get("producer1 message " + 0);
for (int i = 0; i < msgCount; i++)
{
String receiver = messageReceiverMap.get("producer1 message " + i);
if (!trueReceiver.equals(receiver))
{
System.out.println("Group message [producer1 message " + i + "] went to wrong receiver: " + receiver);
result = false;
}
receiver = messageReceiverMap.get("producer2 message " + i);
if (!trueReceiver.equals(receiver))
{
System.out.println("Group message [producer2 message " + i + "] went to wrong receiver: " + receiver);
result = false;
}
}
</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#message-grouping2">Message Grouping chapter</a></li>
</ul>
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