Sample 272:Publishing and Subscribing using WSO2 ESB's MQ Telemetry Transport

Introduction

This sample demonstrates how WSO2 ESB's MQ Telemetry Transport (MQTT) listener consumes messages from a MQTT topic, and how the MQ Telemetry Transport (MQTT) sender publishes messages to a MQTT topic.

Prerequisites

Download the org.eclipse.paho.client.mqttv3-1.1.0.jar file.
Download the Mosquitto-clients (http://mosquitto.org/)
Download WSO2 MB 3.1.0 or the mosquitto MQTT broker (http://mosquitto.org/)

Building the sample

Copy the org.eclipse.paho.client.mqttv3-1.1.0.jar file to the <ESB_HOME>/repository/components/lib directory.

Edit the <ESB_HOME>/repository/conf/axis2/axis2.xml file and change the MQTT sender and listener configuration to be as follows:

<transportReceiver class="org.apache.axis2.transport.mqtt.MqttListener" name="mqtt">
        <parameter locked="false" name="mqttConFactory">
                <parameter locked="false" name="mqtt.server.host.name">localhost</parameter>
                <parameter locked="false" name="mqtt.server.port">1883</parameter>
                <parameter locked="false" name="mqtt.client.id">esb.test.listener</parameter>
                <parameter locked="false" name="mqtt.topic.name">esb.test2</parameter>
        </parameter>
    </transportReceiver>

<transportsender class="org.apache.axis2.transport.mqtt.MqttSender" name="mqtt">
</transportsender>

Start the MQTT broker. If you are using WSO2 MB as the MQTT broker, you should set the WSO2 ESB port offset to 1 before running the ESB. To set the port offset in WSO2 ESB, open the <ESB_HOME>/repository/conf/carbon.xml file and set the offset to 1 as follows:
```
<Offset>1</Offset>
```
Start WSO2 MB, open the Management Console and create a topic named esb.test2.

Start the ESB with the sample 272 configuration. For instructions on starting a sample ESB configuration, see Starting the ESB with a sample configuration. The XML configuration for this sample is as follows:

<definitions xmlns="http://ws.apache.org/ns/synapse">
    <proxy name="SampleProxy" transports="mqtt" startOnLoad="true" trace="disable">
        <description/>
        <target>
            <endpoint>
                <address uri="mqtt:/SampleProxy?mqtt.server.host.name=localhost&amp;mqtt.server.port=1883&amp;mqtt.client.id=esb.test.sender&amp;mqtt.topic.name=esb.test2&amp;mqtt.subscription.qos=2&amp;mqtt.blocking.sender=true"/>
            </endpoint>
            <inSequence>
                <property name="OUT_ONLY" value="true"/>
                <property name="FORCE_SC_ACCEPTED" value="true" scope="axis2" type="STRING"/>
            </inSequence>
            <outSequence>
                <send/>
            </outSequence>
        </target>
        <parameter name="mqtt.connection.factory">mqttConFactory</parameter>
        <parameter name="mqtt.topic.name">esb.test2</parameter>
        <parameter name="mqtt.subscription.qos">2</parameter>
        <parameter name="mqtt.content.type">text/plain</parameter>
        <parameter name="mqtt.session.clean">false</parameter>
    </proxy>
</definitions>

This configuration file synapse_sample_272.xml is available in the <ESB_HOME>/repository/samples directory.

Executing the sample

Execute the following command to start the MQTT subscriber on the esb.test2 topic:
```
mosquitto_sub -h localhost -t esb.test2
```
Execute the following command to run the MQTT publisher to publish to the esb.test1 topic:
```
mosquitto_pub -h localhost -p 1883 -t esb.test1  -m {"company":"WSO2"}
```

Analyzing the output

When you analyze the output messages on the MQTT subscriber console, you will see the following log:

{"company":"WSO2"}