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<h1>JMS XA with JTA Example</h1>
<p>This example shows you how to use JTA interfaces to control transactions with HornetQ. JTA provides
facilities to start and stop a transaction and enlist XA resources into a transaction.</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 get a transaction manager from JBoss JTA to control the transactions. First we create an XASession
for receiving and a normal session for sending. Then we start a new xa transaction and enlist the receiving
XASession through its XAResource. We then send two words, 'hello' and 'world', receive them, and let the
transaction roll back. The received messages are cancelled back to the queue. Next we start
a new transaction with the same XAResource enlisted, but this time we commit the transaction after receiving the
messages. Then we check that no more messages are to be received. In each transaction a dummy XAResource is also
enlisted to show the transaction processing information.</p>
<h2>Example step-by-step</h2>
<p><i>To run the example, simply type <code>mvn verify</code> from this directory. It will download the JBoss JTA jars before
it launches the example.</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>
<pre class="prettyprint">
<code>connection = cf.createXAConnection();</code>
</pre>
<li>We Start the connection</li>
<pre class="prettyprint">
<code>connection.start();</code>
</pre>
<li>We create a JMS XASession</li>
<pre class="prettyprint">
<code>XASession xaSession = connection.createXASession();</code>
</pre>
<li>We create a normal session</li>
<pre class="prettyprint">
<code>Session normalSession = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
</pre>
<li>We create a normal Message Producer</li>
<pre class="prettyprint">
<code>
MessageProducer normalProducer = normalSession.createProducer(queue);
</code>
</pre>
<li>We get the JMS Session</li>
<pre class="prettyprint">
<code>Session session = xaSession.getSession();</code>
</pre>
<li>We create a message consumer</li>
<pre class="prettyprint">
<code>MessageConsumer xaConsumer = session.createConsumer(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 get the Transaction Manager</li>
<pre class="prettyprint">
<code>javax.transaction.TransactionManager txMgr = TransactionManager.transactionManager();</code>
</pre>
<li>We start a transaction</li>
<pre class="prettyprint">
<code>txMgr.begin();</code>
</pre>
<li>We get the JMS XAResource</li>
<pre class="prettyprint">
<code>XAResource xaRes = xaSession.getXAResource();</code>
</pre>
<li>We enlist the resources in the Transaction work</li>
<pre class="prettyprint">
<code>
Transaction transaction = txMgr.getTransaction();
transaction.enlistResource(new DummyXAResource());
transaction.enlistResource(xaRes);
</code>
</pre>
<li>We send two messages.</li>
<pre class="prettyprint">
<code>
normalProducer.send(helloMessage);
normalProducer.send(worldMessage);
</code>
</pre>
<li>We receive the messages</li>
<pre class="prettyprint">
<code>
TextMessage rm1 = (TextMessage)xaConsumer.receive();
System.out.println("Message received: " + rm1.getText());
TextMessage rm2 = (TextMessage)xaConsumer.receive();
System.out.println("Message received: " + rm2.getText());
</code>
</pre>
<li>We roll back the transaction</li>
<pre class="prettyprint">
<code>txMgr.rollback();</code>
</pre>
<li>We create another transaction </li>
<pre class="prettyprint">
<code>
txMgr.begin();
transaction = txMgr.getTransaction();
</code>
</pre>
<li>We enlist the resources to start the transaction work</li>
<pre class="prettyprint">
<code>
transaction.enlistResource(new DummyXAResource());
transaction.enlistResource(xaRes);
</code>
</pre>
<li>We receive those messages again</li>
<pre class="prettyprint">
<code>
rm1 = (TextMessage)xaConsumer.receive();
System.out.println("Message received again: " + rm1.getText());
rm2 = (TextMessage)xaConsumer.receive();
System.out.println("Message received again: " + rm2.getText());
</code>
</pre>
<li>We commit</li>
<pre class="prettyprint">
<code>txMgr.commit();</code>
</pre>
<li>We check that no more messages are received.</li>
<pre class="prettyprint">
<code>
TextMessage rm3 = (TextMessage)xaConsumer.receive(2000);
if (rm3 == null)
{
System.out.println("No message received after commit.");
}
else
{
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>
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