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< title > ActiveMQ JMS Failover With Transaction Example< / title >
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< h1 > JMS Failover With Transaction Example< / h1 >
< p > This example demonstrates two servers coupled as a live-backup pair for high availability (HA), and a client
connection failing over from live to backup when the live server is crashed.< / p >
< p > Failover behavior differs whether the JMS session is transacter or not.< / p >
< p > When a < em > transacted< / em > JMS session is used, once-and-only once delivery is guaranteed.< / p >
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< li > if the failover occurs while there is an in-flight transaction, the transaction will be flagged as < em > rollback only< / em > . In that case, the JMS client
will need to retry the transaction work.< / li >
< li > if the failover occurs while there is < em > no< / em > in-flight transaction, the failover will be transparent to the user.< / li >
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< p > ActiveMQ also provides an example for < a href = "../non-transactional-failover/readme.html" > non-transaction failover< / a > .< / p >
< p > For more information on ActiveMQ failover and HA, and clustering in general, please see the clustering
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section of the user manual.< / p >
< h2 > Example step-by-step< / h2 >
< p > < i > To run the example, simply type < code > mvn verify< / code > from this directory< / i > < / p >
< p > In this example, the live server is server 1, and the backup server is server 0< / p >
< p > The connection will initially be created to server1, server 1 will crash, and the client will carry on
seamlessly on server 0, the backup server.< / p >
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< li > Get an initial context for looking up JNDI from server #1.< / li >
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initialContext = getContext(1);
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< li > Look up the JMS resources from JNDI on server #1.< / li >
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Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
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< li > Create a JMS Connection< / li >
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connection = connectionFactory.createConnection();
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< li > Create a JMS < em > transacted< / em > Session< / li >
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Session session = connection.createSession(true, 0);
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< li > Start the connection to ensure delivery occurs< / li >
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connection.start();
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< li > Create a JMS MessageProducer< / li >
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MessageProducer producer = session.createProducer(queue);
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< li > Create a JMS MessageConsumer< / li >
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MessageConsumer consumer = session.createConsumer(queue);
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< li > Send half of the messages, kill the live server and send the remaining messages< / li >
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sendMessages(session, producer, numMessages, true);
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< p > When server #1 crashes, the client automatically detects the failure and automatically
fails over from server #1 to server #0 (in your real program you wouldn't need to sleep).
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< li > As failover occurred during transaction, the session has been marked for < em > rollback only< / em > and commit will fail< / li >
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try
{
session.commit();
} catch (TransactionRolledBackException e)
{
System.err.println("transaction has been rolled back: " + e.getMessage());
}
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< li > We resend all the messages< / li >
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sendMessages(session, producer, numMessages, false);
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< li > We commit the session successfully: the messages will be all delivered to the activated backup server< / li >
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session.commit();
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< li > We are now transparently reconnected to server #0, the backup server.
We consume the messages sent before the crash of the live server, commit the session, and check there are no other message on the queue< / li >
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for (int i = 0; i < numMessages; i++)
{
TextMessage message0 = (TextMessage)consumer.receive(5000);
System.out.println("Got message: " + message0.getText());
}
session.commit();
System.out.println("Other message on the server? " + consumer.receive(5000));
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< li > And finally, < strong > always< / strong > remember to close your 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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finally
{
if (connection != null)
{
connection.close();
}
if (initialContext != null)
{
initialContext.close();
}
}
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