SubscriptionToTopic.java

/**
* Used for subscribing to the topic.
*/
 private void subscribeToTopic() {
 try {
   mqttAndroidClient.subscribe(subscriptionTopic, 0, null, new IMqttActionListener() {
     @Override
     public void onSuccess(IMqttToken asyncActionToken) {
       Log.w(TAG, "Subscribed!");
     }
     @Override
     public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
       Log.w(TAG, "Subscribed fail!");
     }
  });
 } catch (MqttException ex) {
   Log.e(TAG, "Exception whilst subscribing");
   ex.printStackTrace();
  } 
}