Subscribing to topics and understanding notification events in Java
The onSuccess method prints a message indicating that the client has successfully connected with the MQTT server and then calls the mqttAsyncClient.subscribe method with topic_for_led01 as the argument that specifies the topic filter to subscribe to 0 for the argument that specifies the desired QoS level, null for the userContext argument, and another anonymous class that implements the IMqttActionListener interface as the value for the callback argument. As happened with the connect method, the subscribe method requires the callback argument of the org.eclipse.paho.client.mqttv3.IMqttActionListener type. The anonymous class provides implementations for the previously explained two methods required by the IMqttActionListener interface: onSuccess and onFailure.
The code in the onSuccess method prints a message indicating that the client has subscribed to the topic filter and the granted QoS level. The asyncActionToken.getGrantedQoS...
