2015-07-15 09:05:11 -04:00
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<html>
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<head>
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<title>ActiveMQ Artemis MQTT Example</title>
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2015-08-10 10:41:52 -04:00
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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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2015-07-15 09:05:11 -04:00
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</head>
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<body onload="prettyPrint()">
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<h1>MQTT Example</h1>
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<p>This is a basic MQTT example that demonstrates how to setup and connect to an Apache Artemis broker and
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send and receive messages using the MQTT protocol.</p>
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<h2>Setting up the server</h2>
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<p>This example will use the default out of the box configuration of Artemis you don't need to change anything to run
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this example. Artemis ships with all protocols enabled on port 61616 and also MQTT on port 1883. To enable MQTT
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on a different port you can add the following XML snippet to the 'acceptors' section of your broker.xml
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configuration file (changing the port from 1883 to what ever you require).</p>
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<pre class="prettyprint">
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<!-- Escaped: <acceptor name="hornetq">tcp://0.0.0.0:1883?protocols=MQTT"></acceptor> -->
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<acceptor name="hornetq">tcp://0.0.0.0:1883?protocols=MQTT"></acceptor>
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</pre>
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For more information on configuring protocol transports see the "Configuring Transports" section of the user
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manual, specifically the section called "Single Port Support".
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<h2>MQTT Clients</h2>
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<p>There are a number of MQTT client implementations for various languages. The Paho project:
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http://www.eclipse.org/paho/ offers a number of clients for languages such as C, Python, JavaScript and .Net and
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is also a great resource for all things MQTT.
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This example is actually based on the Fuse MQTT java client and was chosen as it is Apache 2.0 licensed and
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available to download from maven central. The specific client used in the example is not of importance and is
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used simply to demonstrate the features of MQTT as provided by Apache Artemis.</p>
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<p>If you'd like to use the client demonstrated in this example, simple add the following dependency to your
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pom.xml</p>
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<pre class="prettyprint">
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<dependency>
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<groupId>org.fusesource.mqtt-client</groupId>
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<artifactId>mqtt-client</artifactId>
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<version>1.10</version>
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</dependency>
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</pre>
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<h2>Example Step by Step</h2>
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<o1>
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<li>1. Connect to Artemis</li>
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<p>We start by creating a connection to the Apache Artemis broker. In this example we specify to use TCP
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protocol on localhost. By default Apache Artemis will start all protocols on port 61616, so we connect
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to that port.</p>
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<pre class="prettyprint">
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MQTT mqtt = new MQTT();
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mqtt.setHost("tcp://localhost:61616");
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BlockingConnection connection = mqtt.blockingConnection();
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connection.connect();
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</pre>
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<li>2. Create subscriptions</li>
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<p>Subscriptions in MQTT are realised by subscribing to a particular Topic. Each Topic has an address
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and a quality of service level (QoS level). Subscriptions also support wildcards. In the code below we
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subscribe to a Topic with address "mqtt/example/publish" and also a wildcard address "mqtt/#" which will
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match anything starting with "mqtt/".</p>
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<pre class="prettyprint">
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Topic[] topics = { new Topic("mqtt/example/publish", QoS.AT_LEAST_ONCE), new Topic("mqtt/#", QoS.EXACTLY_ONCE) };
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connection.subscribe(topics);
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</pre>
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<li>3. Sending messages</li>
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<p>There is no type system in MQTT, messages simply consist of a number of bytes. Below we send two messages with
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UTF8 encoded strings (as a byte array). Notice the second message is sent to "mqtt/test" which should match
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our wildcard subscription we defined previously.</p>
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<pre class="prettyprint">
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String payload1 = "This is message 1";
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String payload2 = "This is message 2";
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connection.publish("mqtt/example/publish", payload1.getBytes(), QoS.AT_LEAST_ONCE, false);
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connection.publish("mqtt/test", payload2.getBytes(), QoS.AT_MOST_ONCE, false);
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</pre>
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<li>4. Receiving messages</li>
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<p>Since we have subscribed to a number of topics and sent messages to them, the client should now receive
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2 messages. We are not using callbacks here on message receive so we specifically call receive to get
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the messages. Once we recieve the message we convert the payload consisting of bytes back to a UTF8
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encoded string and print the result.</p>
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<pre class="prettyprint">
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Message message1 = connection.receive(5, TimeUnit.SECONDS);
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Message message2 = connection.receive(5, TimeUnit.SECONDS);
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System.out.println(new String(message1.getPayload()));
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System.out.println(new String(message2.getPayload()));
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</pre>
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</o1>
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<h2>Result</h2>
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This example has shown you how to set up the basics of MQTT including how to connect to the Artemis broker and
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how to send and receive messages including subscriptions using wildcard addresses.
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</body>
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</html>
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