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<h1>JMS XA Receive Example</h1>
<p>This example demonstrates receiving a message within the scope of an XA transaction. When using an XA transaction
the message will only be acknowledged and removed from the queue when the transaction is committed.
If the transaction is not committed the message maybe redelivered after rollback or during XA recovery.</p>
<p>ActiveMQ is JTA aware, meaning you can use ActiveMQ in an 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
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.</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>
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<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 Producer</li>
<pre class="prettyprint">
<code>
MessageProducer normalProducer = normalSession.createProducer(queue);
</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 consumer</li>
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<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 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 send two messages.</li>
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<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 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 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 receive those messages again</li>
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<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 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 commit!</li>
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<code>xaRes.commit(xid2, false);</code>
</pre>
<li>We check that no more messages are received.</li>
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<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>
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<code>finally
{
if (initialContext != null)
{
initialContext.close();
}
if (connection != null)
{
connection.close();
}
}</code>
</pre>
</ol>
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