Experimental servlet which connects to a MQTT topic, and forwards any messages it receives over WebSocket.

Status

This project should run out of the box, it has been tested running a local Mosquitto test broker (see below).

Usage

To test with everything running locally, take the following steps.

• You need a MQTT broker, I am testing with Mosquitto. Download and install.
• Open a command prompt and start the Mosquitto broker: mosquitto.
• Open a second command prompt and start the test servlet: mvn jetty:run.
• Wait until maven has finished downloading dependencies (first run only). In the log you should see the following messages

    [INFO] Started Jetty Server
    2013-05-27 22:26:02,684 [MqttRelayServlet$TestConnectionListener] DEBUG - onConnected()
    2013-05-27 22:26:02,686 [MqttRelayServlet$TestConnectionCallback] INFO  - Successfully subscribed to topic TT

• Open a third command prompt and use the provided mosquitto client to send a test message: mosquitto_pub -t TT -m "Test"
• The Jetty log should show messages indicating that the callback was called, and should log the message text.
• Open a browser (with WebSocket support) and go to http://localhost:8080/relay.html
• Click the "connect" button, the message box should show a message like Mon May 27 22:26:13 CEST 2013 websocket connected and added to receiver list. The websocket connection to the server is now active.
• Go to the command prompt with the mosquitto client again and send another message: mosquitto_pub -t TT -m "Test2"
• The Jetty log should again show a message; if you go to the web page the message you just sent should be in the message box.

Configuration

The configuration is in src/main/webapp/WEB-INF/web.xml . In this file the following section configures the relay servlet:

<servlet>
    <servlet-name>RelayServlet</servlet-name>
    <servlet-class>org.vanbart.MqttRelayServlet</servlet-class>
    <init-param>
        <description>host of the MQTT server (defaults to localhost if omitted)</description>
        <param-name>host</param-name>
        <param-value>localhost</param-value>
    </init-param>
    <init-param>
        <description>Name of the MQTT topic to listen on</description>
        <param-name>topic</param-name>
        <param-value>TT</param-value>
    </init-param>
    <load-on-startup>0</load-on-startup>
</servlet> 

See the description of the init parameters; you can configure the host where the MQTT broker lives, and the topic to listen to. The port number is hardcoded to 1883 (the MQTT default port).
If you change the topic name, in the commands above the -t parameter should be adjusted to the new value (obviously). After you change the values you have to restart the server to make the changes active.

License

This project is licensed under the Apache License, Version 2.0