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<h1>JMS XA Send Example</h1>
<p>This example shows you how message sending behaves in an XA transaction in HornetQ. When a message is sent within
the scope of an XA transaction, it will only reach the queue once the transaction is committed.
If the transaction is rolled back the sent messages will be discarded by the server.</p>
<p>HornetQ is JTA aware, meaning you can use HornetQ in a XA transactional environment
and participate in XA transactions. It provides the javax.transaction.xa.XAResource interface for that
purpose. Users can get a XAConnectionFactory to create XAConnections and XASessions.</p>
<p>In this example we simulate a transaction manager to control the transactions. First we create an XASession
and enlist it in a transaction through its XAResource. We then send two words, 'hello' and 'world', with
the session, let the transaction roll back. The messages are discarded and never be received. Next we start
a new transaction with the same XAResource, but this time we commit the transaction. Both messages are received.</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(0);</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 perform a lookup on the XA Connection Factory</li>
<pre class="prettyprint">
<code>XAConnectionFactory cf = (XAConnectionFactory) initialContext.lookup("/XAConnectionFactory");</code>
</pre>
<li>We create a JMS XAConnection</li>
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<code>connection = cf.createXAConnection();</code>
</pre>
<li>We Start the connection</li>
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<code>connection.start();</code>
</pre>
<li>We create a JMS XASession</li>
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<code>XASession xaSession = connection.createXASession();</code>
</pre>
<li>We create a normal session</li>
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<code>Session normalSession = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
</pre>
<li>We create a normal Message Consumer</li>
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<code>
MessageConsumer normalConsumer = normalSession.createConsumer(queue);
normalConsumer.setMessageListener(new SimpleMessageListener());
</code>
</pre>
<li>We get the JMS Session</li>
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<code>Session session = xaSession.getSession();</code>
</pre>
<li>We create a message producer</li>
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<code>MessageProducer producer = session.createProducer(queue);</code>
</pre>
<li>We create two Text Messages</li>
<pre class="prettyprint">
<code>
TextMessage helloMessage = session.createTextMessage("hello");
TextMessage worldMessage = session.createTextMessage("world");
</code>
</pre>
<li>We create a transaction</li>
<pre class="prettyprint">
<code>Xid xid1 = new XidImpl("xa-example1".getBytes(), 1, UUIDGenerator.getInstance().generateStringUUID().getBytes());</code>
</pre>
<li>We get the JMS XAResource</li>
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<code>XAResource xaRes = xaSession.getXAResource();</code>
</pre>
<li>We begin the Transaction work</li>
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<code>xaRes.start(xid1, XAResource.TMNOFLAGS);</code>
</pre>
<li>We do work, sending two messages.</li>
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<code>
producer.send(helloMessage);
producer.send(worldMessage);
</code>
</pre>
<li>We check the result, it should receive none!</li>
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<code>checkNoMessageReceived();</code>
</pre>
<li>We stop the work</li>
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<code>xaRes.end(xid1, XAResource.TMSUCCESS);</code>
</pre>
<li>We prepare</li>
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<code>xaRes.prepare(xid1);</code>
</pre>
<li>We roll back the transaction </li>
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<code>xaRes.rollback(xid1);</code>
</pre>
<li>We check no messages should be received! </li>
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<code>checkNoMessageReceived();</code>
</pre>
<li>We create another transaction</li>
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<code>Xid xid2 = new XidImpl("xa-example2".getBytes(), 1, UUIDGenerator.getInstance().generateStringUUID().getBytes());</code>
</pre>
<li>We start the transaction</li>
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<code>xaRes.start(xid2, XAResource.TMNOFLAGS);</code>
</pre>
<li>We re-send those messages</li>
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<code>
producer.send(helloMessage);
producer.send(worldMessage);
</code>
</pre>
<li>We stop the work</li>
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<code>xaRes.end(xid2, XAResource.TMSUCCESS);</code>
</pre>
<li>We prepare</li>
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<code>xaRes.prepare(xid2);</code>
</pre>
<li>We check that no messages should be received at this moment</li>
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<code>checkNoMessageReceived();</code>
</pre>
<li>We commit!</li>
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<code>xaRes.commit(xid2, false);</code>
</pre>
<li>We check that all messages are received.</li>
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<code>checkAllMessageReceived();</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>
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