client.groovy

import groovy.transform.Field
import io.vertx.mqtt.MqttClient
import io.vertx.core.buffer.Buffer
import io.netty.handler.codec.mqtt.MqttQoS
@Field def MQTT_MESSAGE = "Hello Vert.x MQTT Client"
@Field def BROKER_HOST = "localhost"
@Field def BROKER_PORT = 1883
@Field def MQTT_TOPIC = "/my_topic"
def mqttClient = MqttClient.create(vertx)

mqttClient.connect(BROKER_PORT, BROKER_HOST, { ch ->
  if (ch.succeeded()) {
    println("Connected to a server")

    mqttClient.publish(MQTT_TOPIC, Buffer.buffer(MQTT_MESSAGE), MqttQoS.AT_MOST_ONCE, false, false, { s ->
      mqttClient.disconnect({ d ->
        println("Disconnected from server")
      })
    })
  } else {
    println("Failed to connect to a server")
    println(ch.cause())
  }
})