214 lines
8.1 KiB
HTML
214 lines
8.1 KiB
HTML
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<html>
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<head>
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<title>ActiveMQ Artemis JMS Durable Subscription Example</title>
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<link rel="stylesheet" type="text/css" href="../common/common.css" />
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<link rel="stylesheet" type="text/css" href="../common/prettify.css" />
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<script type="text/javascript" src="../common/prettify.js"></script>
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</head>
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<body onload="prettyPrint()">
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<h1>JMS Durable Subscription Example</h1>
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<p>This example demonstrates a clustered JMS durable subscription.
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Normally durable subscriptions exist on a single node and can only have one subscriber at any one time,
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however, with ActiveMQ Artemis it's possible to create durable subscription instances with the same name and client-id
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on different nodes of the cluster, and consume from them simultaneously.
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This allows the work of processing messages from a durable subscription to be spread across the cluster in
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a similar way to how JMS Queues can be load balanced across the cluster
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</p>
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<p>In this example we first configure the two nodes to form a cluster, then we then create a durable subscriber
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with the same name and client-id on both nodes, and we create a producer on only one of the nodes.</p>
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<p>We then send some messages via the producer, and we verify that the messages are round robin'd between
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the two subscription instances. Note that each durable subscription instance with the same name and client-id
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<b>does not</b> receive its own copy of the messages. This is because the instances on different nodes form a
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single "logical" durable subscription, in the same way multiple JMS Queue instances on different nodes
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form a single "local" JMS Queue</p>
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<p>This example uses JNDI to lookup the JMS Queue and ConnectionFactory objects. If you prefer not to use
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JNDI, these could be instantiated directly.
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<p>Here's the relevant snippet from the server configuration, which tells the server to form a cluster between the two nodes
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and to load balance the messages between the nodes.</p>
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<pre class="prettyprint">
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<code><cluster-connection name="my-cluster">
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<address>jms</address>
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<retry-interval>500</retry-interval>
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<use-duplicate-detection>true</use-duplicate-detection>
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<message-load-balancing>STRICT</message-load-balancing>
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<max-hops>1</max-hops>
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<discovery-group-ref discovery-group-name="my-discovery-group"/>
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</cluster-connection>
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</code>
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</pre>
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<p>For more information on ActiveMQ Artemis load balancing, and clustering in general, please see the clustering
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section of the user manual.</p>
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<h2>Example step-by-step</h2>
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<p><i>To run the example, simply type <code>mvn verify -Pexample</code> from this directory</i></p>
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<ol>
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<li> Get an initial context for looking up JNDI from server 0.</li>
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<pre class="prettyprint">
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<code>
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ic0 = getContext(0);
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</code>
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</pre>
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<li>Look-up the JMS Topic object from JNDI</li>
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<pre class="prettyprint">
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<code>Topic topic = (Topic)ic0.lookup("/topic/exampleTopic");</code>
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</pre>
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<li>Look-up a JMS Connection Factory object from JNDI on server 0</li>
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<pre class="prettyprint">
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<code>ConnectionFactory cf0 = (ConnectionFactory)ic0.lookup("/ConnectionFactory");</code>
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</pre>
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<li>Get an initial context for looking up JNDI from server 1.</li>
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<pre class="prettyprint">
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<code>ic1 = getContext(1);</code>
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</pre>
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<li>Look-up a JMS Connection Factory object from JNDI on server 1</li>
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<pre class="prettyprint">
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<code>ConnectionFactory cf1 = (ConnectionFactory)ic1.lookup("/ConnectionFactory");
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</code>
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</pre>
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<li>We create a JMS Connection connection0 which is a connection to server 0
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and set the same client-id.</li>
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<pre class="prettyprint">
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<code>
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connection0 = cf0.createConnection();
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final String clientID = "my-client-id";
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connection0.setClientID(clientID);
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</code>
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</pre>
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<li>We create a JMS Connection connection1 which is a connection to server 1
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and set the same client-id.</li>
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<pre class="prettyprint">
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<code>
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connection1 = cf1.createConnection();
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connection1.setClientID(clientID);
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</code>
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</pre>
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<li>We create a JMS Session on server 0</li>
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<pre class="prettyprint">
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<code>
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Session session0 = connection0.createSession(false, Session.AUTO_ACKNOWLEDGE);
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</code>
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</pre>
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<li>We create a JMS Session on server 1</li>
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<pre class="prettyprint">
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<code>
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Session session1 = connection1.createSession(false, Session.AUTO_ACKNOWLEDGE);
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</code>
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</pre>
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<li>We start the connections to ensure delivery occurs on them</li>
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<pre class="prettyprint">
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<code>
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connection0.start();
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connection1.start();
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</code>
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</pre>
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<li>We create JMS durable subscriptions with the same name and client-id on both nodes
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of the cluster
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</li>
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<pre class="prettyprint">
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<code>
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final String subscriptionName = "my-subscription";
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MessageConsumer subscriber0 = session0.createDurableSubscriber(topic, subscriptionName);
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MessageConsumer subscriber1 = session1.createDurableSubscriber(topic, subscriptionName);
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</code>
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</pre>
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<li>We create a JMS MessageProducer object on server 0.</li>
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<pre class="prettyprint">
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<code>
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MessageProducer producer = session0.createProducer(topic);</code>
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</pre>
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<li>We send some messages to server 0.</li>
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<pre class="prettyprint">
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<code>
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final int numMessages = 10;
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for (int i = 0; i < numMessages; i++)
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{
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TextMessage message = session0.createTextMessage("This is text message " + i);
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producer.send(message);
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System.out.println("Sent message: " + message.getText());
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}
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</code>
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</pre>
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<li>
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We now consume those messages on *both* server 0 and server 1.
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Note that the messages have been load-balanced between the two nodes, with some
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messages on node 0 and others on node 1.
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The "logical" subscription is distributed across the cluster and contains exactly one copy of all the messages sent.
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</li>
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<pre class="prettyprint">
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<code>
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for (int i = 0; i < numMessages; i += 2)
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{
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TextMessage message0 = (TextMessage)consumer0.receive(5000);
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System.out.println("Got message: " + message0.getText() + " from node 0");
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TextMessage message1 = (TextMessage)consumer1.receive(5000);
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System.out.println("Got message: " + message1.getText() + " from node 1");
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}
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</code>
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</pre>
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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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<pre class="prettyprint">
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<code>
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finally
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{
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if (connection0 != null)
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{
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connection0.close();
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}
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if (connection1 != null)
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{
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connection1.close();
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}
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}
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</code>
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</pre>
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</ol>
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</body>
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</html>
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