我正在嘗試使用

Eclipse Paho在Java中的MQTT客戶端上實現某些功能.目標是訂閱主題,并且當收到消息時,客戶端發送關于另一主題的另一消息.

這看起來很容易,但我有一個奇怪的問題,我無法解決.這是我的代碼：

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;

import org.eclipse.paho.client.mqttv3.IMqttToken;

import org.eclipse.paho.client.mqttv3.MqttCallback;

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.MqttClient;

import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class MqttOperations implements MqttCallback {

MqttClient sampleClient;

MqttConnectOptions connOpts;

public MqttOperations() {

}

public static void main(String[] args) throws InterruptedException {

new MqttOperations().launchMqttClient();

}

public void launchMqttClient() throws InterruptedException {

try {

MemoryPersistence persistence = new MemoryPersistence();

sampleClient = new MqttClient("tcp://broker.mqttdashboard.com:1883", "iamaclient", persistence);

connOpts = new MqttConnectOptions();

connOpts.setCleanSession(true);

sampleClient.connect(connOpts);

sampleClient.subscribe("topic/example/ofmessage");

sampleClient.setCallback(this);

} catch(MqttException me) {

System.out.println("reason "+me.getReasonCode());

System.out.println("msg "+me.getMessage());

System.out.println("loc "+me.getLocalizedMessage());

System.out.println("cause "+me.getCause());

System.out.println("excep "+me);

me.printStackTrace();

}

}

@Override

public void connectionLost(Throwable cause) {

// TODO Auto-generated method stub

}

@Override

public void messageArrived(String topic, MqttMessage message) throws MqttException

{

System.out.println("Received: " + message.toString());

try{

System.out.println("Publishing message: i am the answer");

MqttMessage ans = new MqttMessage("i am the answer".getBytes());

ans.setQos(2);

sampleClient.publish("topic/example/ofanswer", ans);

System.out.println("Message published");

}catch(MqttException me){

System.out.println("reason "+me.getReasonCode());

System.out.println("msg "+me.getMessage());

System.out.println("loc "+me.getLocalizedMessage());

System.out.println("cause "+me.getCause());

System.out.println("excep "+me);

me.printStackTrace();

}

}

@Override

public void deliveryComplete(IMqttDeliveryToken token) {

}

}

問題是,這個程序只運行一次.收到消息后,將發送此消息的答案,但似乎消息“消息已發布”從未顯示在屏幕上,并且客戶端不會收到任何其他消息.

我有這樣的印象,即sampleClient.publish行(“topic / example / ofanswer”,ans);永遠不會完成它的執行.

有誰知道它是怎么來的,請問如何解決我的問題？

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