MQTTJavaAndroïd - 订阅$ SYS /＃

Question

我正在使用paho订阅mqtt主题“$ SYS /＃”，以便查看客户端的连接。

我在本主题中实现了MqttCallback接口以接收消息发送，目前我只想在控制台中显示消息内容。

我的问题是无休止地接收消息，“messageArrived”函数每秒调用一次，并且始终具有相同的客户端名称。

import android.app.Activity;

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class MainActivity extends Activity {
    private static final String MQTT_DIR = "/home/persistence.log";
    private static final String MQTT_URI = "tcp://x.x.x.x:1883";
    private MqttClient client;

    private String clientId = "AndroidClient";
    private String clientName = "usermqtt";
    private char[] password = {'x', 'x', 'x'};

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        MemoryPersistence persistence = new MemoryPersistence();
        MqttConnectOptions options = new MqttConnectOptions();

        options.setUserName(clientName);
        options.setPassword(password);

        try {
            client = new MqttClient(MQTT_URI, clientId, persistence);
            client.connect(options);
            client.subscribe("$SYS/#");
        } catch (MqttException e) {
            e.printStackTrace();
        }

        client.setCallback(new MqttCallback() {
            @Override
            public void connectionLost(Throwable throwable) {
            }

            @Override
            public void messageArrived(String arg0, MqttMessage arg1)  
            throws Exception {
                // TODO Auto-generated method stub
                System.out.println("Message Received");
                System.out.println(arg0);
                System.out.println(arg1.toString());
            }

            @Override
            public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
            }
        });
}