我正在尝试使用
Eclipse Paho在Java中的MQTT客户端上实现某些功能.目标是订阅主题,并且当收到消息时,客户端发送关于另一主题的另一消息.
这看起来很容易,但我有一个奇怪的问题,我无法解决.这是我的代码：
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://: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) {
}
}
问题是,这个程序只运行一次.收到消息后,将发送此消息的答案,但似乎消息“消息已发布”从未显示在屏幕上,并且客户端不会收到任何其他消息.
我有这样的印象,即sampleClient.publish行(“topic / example / ofanswer”,ans);永远不会完成它的执行.
有谁知道它是怎么来的,请问如何解决我的问题？
