20200318 MQTT Groovy Example

I am interested in MQTT since the beginning of 2020.

This is Groovy example code for a client connecting to a MQTT server, which subscribes for a topic tree, parses payloads and publishes information.

I have seen the original version of this code here :

https://cumulocity.com/guides/device-sdk/mqtt-examples/#hello-mqtt-java

  package de.wartbar.mqtt

  import org.eclipse.paho.client.mqttv3.*
  import java.util.concurrent.*

  class MqttClientWartbar {

      def static startClient() {

          final String serverUrl = "tcp://localhost"
          final String clientId = "my_mqtt_java_client"
          final String tenant = ""
          final String username = "user"
          final String password = "password"

          final MqttConnectOptions options = new MqttConnectOptions()
          options.setUserName(tenant + "/" + username)
          options.setPassword(password.toCharArray())

          final MqttClient client = new MqttClient(serverUrl, clientId, null)
          client.connect(options)

          client.publish("client/" + clientId + "/status", ("registered").getBytes(), 2, true)

          client.subscribe("client/#", new IMqttMessageListener() {
              public void messageArrived(final String topic, final MqttMessage message) throws Exception {
                  final String payload = new String(message.getPayload())

                  System.out.println("Received topic " + topic)
                  System.out.println("Received payload " + payload)
                  if (payload.startsWith("reactOn")) {
                      Executors.newSingleThreadScheduledExecutor().execute(new Runnable() {
                          public void run() {
                              try {
                                  System.out.println("I react on :" + payload)
                                  client.publish("client/" + clientId + "/reaction1",("reacted on " + payload).getBytes(), 2, false)
                                  client.publish("client/" + clientId + "/reaction2", new MqttMessage(("reacted on " + payload).getBytes()))
                             } catch (MqttException e) {
                                  e.printStackTrace()
                              } catch (InterruptedException e) {
                                  e.printStackTrace()
                              }
                          }
                      })
                  }
              }
          })

          while (true) {
              System.out.println(".")
              sleep(1000)
          }
      }
  }