org.eclipse.paho.client mqtt客戶端連接超時

客戶端訂閱mqtt 的時候 顯示超時。第二次重起服務可能就好了，但是可能會丟消息。

報錯如下

org.eclipse.paho.client.mqttv3.MqttException: 等待來自服務器的響應時超時
        at org.eclipse.paho.client.mqttv3.internal.ExceptionHelper.createMqttException(ExceptionHelper.java:31) ~[org.eclipse.paho.client.mqttv3-1.2.1.jar!/:na]
        at org.eclipse.paho.client.mqttv3.internal.ClientState.checkForActivity(ClientState.java:741) ~[org.eclipse.paho.client.mqttv3-1.2.1.jar!/:na]
        at org.eclipse.paho.client.mqttv3.internal.ClientComms.checkForActivity(ClientComms.java:816) ~[org.eclipse.paho.client.mqttv3-1.2.1.jar!/:na]
        at org.eclipse.paho.client.mqttv3.internal.ClientComms.checkForActivity(ClientComms.java:802) ~[org.eclipse.paho.client.mqttv3-1.2.1.jar!/:na]
        at org.eclipse.paho.client.mqttv3.TimerPingSender$PingTask.run(TimerPingSender.java:79) ~[org.eclipse.paho.client.mqttv3-1.2.1.jar!/:na]
        at java.util.TimerThread.mainLoop(Timer.java:555) ~[na:1.8.0_221]
        at java.util.TimerThread.run(Timer.java:505) ~[na:1.8.0_221]

　　解決辦法:

 

log.info("try connect to mqtt");
//調用connect 后，一定要再調用 一下token.waitForCompletion();這樣應該就可以了。原因不明。

IMqttToken token = client.connect(connOpts);
token.waitForCompletion();
log.info("connect mqtt success");
client.subscribe(topic, 1, new MqttMsgListener());