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< title > ActiveMQ JMS Clustered Topic Example< / title >
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< h1 > JMS Clustered Topic Example< / h1 >
< p > This example demonstrates a JMS Topic deployed on two different nodes. The two nodes are configured to form a cluster.< / p >
< p > We then create a subscriber on the topic on each node, and we create a producer on only one of the nodes.< / p >
< p > We then send some messages via the producer, and we verify that < b > both< / b > subscribers receive all the
sent messages.< / p >
< p > A JMS Topic is an example of < b > publish-subscribe< / b > messaging where all subscribers receive all the
messages sent to the topic (assuming they have no message selectors).< / p >
< p > This example uses JNDI to lookup the JMS Queue and ConnectionFactory objects. If you prefer not to use
JNDI, these could be instantiated directly.
< p > Here's the relevant snippet from the server configuration, which tells the server to form a cluster between the two nodes
and to load balance the messages between the nodes.< / p >
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< code > < cluster-connection name="my-cluster">
< address> jms< /address>
< retry-interval> 500< /retry-interval>
< use-duplicate-detection> true< /use-duplicate-detection>
< forward-when-no-consumers> true< /forward-when-no-consumers>
< max-hops> 1< /max-hops>
< discovery-group-ref discovery-group-name="my-discovery-group"/>
< /cluster-connection>
< / code >
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< p > For more information on ActiveMQ load balancing, 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 >
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< li > Get an initial context for looking up JNDI from server 0.< / li >
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ic0 = getContext(0);
< / code >
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< li > Look-up the JMS Topic object from JNDI< / li >
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< code > Topic topic = (Topic)ic0.lookup("/topic/exampleTopic");< / code >
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< li > Look-up a JMS Connection Factory object from JNDI on server 0< / li >
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< code > ConnectionFactory cf0 = (ConnectionFactory)ic0.lookup("/ConnectionFactory");< / code >
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< li > Get an initial context for looking up JNDI from server 1.< / li >
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< code > ic1 = getContext(1);< / code >
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< li > Look-up a JMS Connection Factory object from JNDI on server 1< / li >
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< code > ConnectionFactory cf1 = (ConnectionFactory)ic1.lookup("/ConnectionFactory");
< / code >
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< li > We create a JMS Connection connection0 which is a connection to server 0< / li >
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< code >
connection0 = cf0.createConnection();
< / code >
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< li > We create a JMS Connection connection1 which is a connection to server 1< / li >
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< code >
connection1 = cf1.createConnection();
< / code >
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< li > We create a JMS Session on server 0< / li >
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< code >
Session session0 = connection0.createSession(false, Session.AUTO_ACKNOWLEDGE);
< / code >
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< li > We create a JMS Session on server 1< / li >
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< code >
Session session1 = connection1.createSession(false, Session.AUTO_ACKNOWLEDGE);
< / code >
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< li > We start the connections to ensure delivery occurs on them< / li >
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< code >
connection0.start();
connection1.start();
< / code >
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< li > We create JMS MessageConsumer (Topic subscriber) objects on server 0 and server 1< / li >
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< code >
MessageConsumer consumer0 = session0.createConsumer(topic);
MessageConsumer consumer1 = session1.createConsumer(topic);
< / code >
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< li > We create a JMS MessageProducer object on server 0.< / li >
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< code >
MessageProducer producer = session0.createProducer(topic);< / code >
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< li > We send some messages to server 0.< / li >
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< code >
final int numMessages = 10;
for (int i = 0; i < numMessages ; i + + )
{
TextMessage message = session0.createTextMessage("This is text message " + i);
producer.send(message);
System.out.println("Sent message: " + message.getText());
}
< / code >
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< li >
We now consume those messages on < b > both< / b > server 0 and server 1.
We note that all messages have been consumed by < b > both< / b > consumers.
JMS Topics implement < b > publish-subscribe< / b > messaging where all consumers get a copy of all messages.
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for (int i = 0; i < numMessages ; i + + )
{
TextMessage message0 = (TextMessage)consumer0.receive(5000);
System.out.println("Got message: " + message0.getText() + " from node 0");
TextMessage message1 = (TextMessage)consumer1.receive(5000);
System.out.println("Got message: " + message1.getText() + " from node 1");
}
< / code >
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< li > And finally (no pun intended), < b > always< / b > remember to close your JMS 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 (connection0 != null)
{
connection0.close();
}
if (connection1 != null)
{
connection1.close();
}
}
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