Scala MQTT Client

MQTT is broker based message queuing system. So to work with MQTT, MQTT Message broker/server required. Mosquitto is an open source MQTT Broker. In Ubuntu mosquitto can be installed using the command

$ sudo apt-get install mosquitto

Eclipse Paho is one mqtt client work well with mosquitto. You may read more about it here.

MQTT Scala Publisher

package main.scala

import org.eclipse.paho.client.mqttv3.MqttClient
import org.eclipse.paho.client.mqttv3.MqttException
import org.eclipse.paho.client.mqttv3.MqttMessage
import org.eclipse.paho.client.mqttv3.persist.MqttDefaultFilePersistence

/**
 *
 * MQTT publisher
 * @author Prabeesh K
 * @mail [email protected]
 *
 */

object Publisher {

  def main(args: Array[String]) {
    val brokerUrl = "tcp://localhost:1883"
    val topic = "foo"
    val msg = "Hello world test data"

    var client: MqttClient = null

    // Creating new persistence for mqtt client
    val persistence = new MqttDefaultFilePersistence("/tmp")

    try {
      // mqtt client with specific url and client id
      client = new MqttClient(brokerUrl, MqttClient.generateClientId, persistence)

      client.connect()

      val msgTopic = client.getTopic(topic)
      val message = new MqttMessage(msg.getBytes("utf-8"))

      while (true) {
        msgTopic.publish(message)
        println("Publishing Data, Topic : %s, Message : %s".format(msgTopic.getName, message))
        Thread.sleep(100)
      }
    }

    catch {
      case e: MqttException => println("Exception Caught: " + e)
    }

    finally {
      client.disconnect()
    }
  }
}

MQTT Scala Subscriber

package main.scala

import org.eclipse.paho.client.mqttv3._
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence

/**
 *
 * MQTT subcriber
 * @author Prabeesh K
 * @mail [email protected]
 *
 */

object Subscriber {

  def main(args: Array[String]) {

    val brokerUrl = "tcp://localhost:1883"
    val topic = "foo"

    //Set up persistence for messages 
    val persistence = new MemoryPersistence

    //Initializing Mqtt Client specifying brokerUrl, clientID and MqttClientPersistance
    val client = new MqttClient(brokerUrl, MqttClient.generateClientId, persistence)

    //Connect to MqttBroker    
    client.connect

    //Subscribe to Mqtt topic
    client.subscribe(topic)

    //Callback automatically triggers as and when new message arrives on specified topic
    val callback = new MqttCallback {

      override def messageArrived(topic: String, message: MqttMessage): Unit = {
        println("Receiving Data, Topic : %s, Message : %s".format(topic, message))
      }

      override def connectionLost(cause: Throwable): Unit = {
         println(cause)
       }

      override def deliveryComplete(token: IMqttDeliveryToken): Unit = {

      }
    }

    //Set up callback for MqttClient
    client.setCallback(callback)

  }
}

SBT file

name := "MQTTScalaClinet"

version := "0.2.0"

scalaVersion := "2.10.3"

libraryDependencies += "org.eclipse.paho" % "mqtt-client" % "0.4.0"

resolvers += "MQTT Repository" at "https://repo.eclipse.org/content/repositories/paho-releases/"

MQTT Scala subscriber and publisher code based on eclipse paho library 0.4.0 is available in github with SBT build tool.