java用mqtt收发消息

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.MqttDeliveryToken;import org.eclipse.paho.client.mqttv3.MqttMessage;import org.eclipse.paho.client.mqttv3.MqttTopic;public class Test {     private static String hostName="tcp://xxx:1883";//"tcp://iot.eclipse.org:1883";    public static String uuid="xxx";public static String token="xx";private static String username= uuid ;private static String password= token ;private static String subscribeTopic= uuid ;private static String publisheTopic= "message" ;private static String sendMsg="{\"devices\":\""+uuid+"\",\"payload\":{\"param1\":\"value1\"}}";private static MqttClient client ;public static void main(String[] args) {     //订阅消息的方法  subscribe();         //发布消息的类  publish();}  public static String subscribe() {           try {               //创建MqttClient          client=new MqttClient(hostName,"11");               client.setCallback(new MqttCallback(){public void connectionLost(Throwable arg0) {}public void deliveryComplete(MqttDeliveryToken arg0) {}public void messageArrived(MqttTopic topic, MqttMessage message)throws Exception {        try {               System.out.println(" 从服务器收到的消息为:"+message.toString());          } catch (Exception e) {               e.printStackTrace();           } }                        });            MqttConnectOptions conOptions = new MqttConnectOptions();               conOptions.setUserName(username);            conOptions.setPassword(password.toCharArray());            conOptions.setCleanSession(false);               client.connect(conOptions);               client.subscribe(subscribeTopic, 1);             boolean isSuccess =client.isConnected();            System.out.println("连接状态:"+isSuccess);            //client.disconnect();           } catch (Exception e) {               e.printStackTrace();               return "failed";           }           return "success";       }       public static void publish(){           try {               MqttTopic topic = client.getTopic(publisheTopic);               System.out.println("发送的消息内容为:"+sendMsg);            MqttMessage message = new MqttMessage(sendMsg.getBytes());               message.setQos(1);               while(true){                  MqttDeliveryToken token = topic.publish(message);                 while (!token.isComplete()){                       token.waitForCompletion(1000);                   }               }          } catch (Exception e) {               e.printStackTrace();           }       }  }