MQTT协议之订阅及发布（使用paho-mqtt-client或mqttv3实现）

另外一个MQTT发布订阅客户端paho-mqtt-client或mqttv3采用回调的方式实现消息的接收，下面看一下实现：

1.消息接收回调类

 package cn.smartslim.mqtt.demo.paho;

 import org.eclipse.paho.client.mqttv3.MqttCallback;
 import org.eclipse.paho.client.mqttv3.MqttDeliveryToken;
 import org.eclipse.paho.client.mqttv3.MqttMessage;
 import org.eclipse.paho.client.mqttv3.MqttTopic;

 /**
  * 发布消息的回调类
  *
  * 必须实现MqttCallback的接口并实现对应的相关接口方法
  *      ◦CallBack 类将实现 MqttCallBack。每个客户机标识都需要一个回调实例。在此示例中，构造函数传递客户机标识以另存为实例数据。在回调中，将它用来标识已经启动了该回调的哪个实例。
  *  ◦必须在回调类中实现三个方法：
  *
  *  public void messageArrived(MqttTopic topic, MqttMessage message)
  *  接收已经预订的发布。
  *
  *  public void connectionLost(Throwable cause)
  *  在断开连接时调用。
  *
  *  public void deliveryComplete(MqttDeliveryToken token))
  *      接收到已经发布的 QoS 1 或 QoS 2 消息的传递令牌时调用。
  *  ◦由 MqttClient.connect 激活此回调。
  *
  */
 public class PushCallback implements MqttCallback {

     public void connectionLost(Throwable cause) {
         // 连接丢失后，一般在这里面进行重连
         System.out.println("连接断开，可以做重连");
     }

     public void deliveryComplete(MqttDeliveryToken token) {
         // publish后会执行到这里
         System.out.println("deliveryComplete---------"+ token.isComplete());
     }

     public void messageArrived(MqttTopic topic, MqttMessage message) throws Exception {
         // subscribe后得到的消息会执行到这里面
         System.out.println("接收消息主题:"+topic.getName());
         System.out.println("接收消息Qos:"+message.getQos());
         System.out.println("接收消息内容:"+new String(message.getPayload()));
     }

 }

2.服务端发布消息

 package cn.smartslim.mqtt.demo.paho;

 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.MqttException;
 import org.eclipse.paho.client.mqttv3.MqttMessage;
 import org.eclipse.paho.client.mqttv3.MqttPersistenceException;
 import org.eclipse.paho.client.mqttv3.MqttTopic;
 import org.eclipse.paho.client.mqttv3.internal.MemoryPersistence;

 public class Server {

     public static final String HOST = "tcp://192.168.36.102:1883";

     public static final String TOPIC = "tokudu/yzq124";
     private static final String clientid ="server";

     private MqttClient client;
     private MqttTopic topic;
     private String userName = "test";
     private String passWord = "test";

     private MqttMessage message;

     public Server() throws MqttException {
          //MemoryPersistence设置clientid的保存形式，默认为以内存保存
         client = new MqttClient(HOST, clientid, new MemoryPersistence());
         connect();
     }

     private void connect() {
         MqttConnectOptions options = new MqttConnectOptions();
         options.setCleanSession(false);
         options.setUserName(userName);
         options.setPassword(passWord.toCharArray());
         // 设置超时时间
         options.setConnectionTimeout(10);
         // 设置会话心跳时间
         options.setKeepAliveInterval(20);
         try {
                client.setCallback(new PushCallback());
                client.connect(options);
                topic = client.getTopic(TOPIC);
         } catch (Exception e) {
                e.printStackTrace();
         }
     }

     public void publish(MqttMessage message) throws MqttPersistenceException, MqttException{
         MqttDeliveryToken token = topic.publish(message);
         token.waitForCompletion();
         System.out.println(token.isComplete()+"========");
     }

     public static void main(String[] args) throws MqttException {
         Server server =  new Server();
         server.message = new MqttMessage();
         server.message.setQos(1);
         server.message.setRetained(true);
         server.message.setPayload("eeeeeaaaaaawwwwww---".getBytes());
          server.publish(server.message);
          System.out.println(server.message.isRetained()+"------ratained状态");
     }

 }

3.客户端接收消息

 package cn.smartslim.mqtt.demo.paho;

 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;

 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.MqttSecurityException;
 import org.eclipse.paho.client.mqttv3.MqttTopic;
 import org.eclipse.paho.client.mqttv3.internal.MemoryPersistence;

 public class Client {

     public static final String HOST = "tcp://192.168.36.102:1883";
     public static final String TOPIC = "tokudu/yzq124";
     private static final String clientid = "client";
     private MqttClient client;
     private MqttConnectOptions options;
     private String userName = "test";
     private String passWord = "test";

     private ScheduledExecutorService scheduler;

     //重新链接
     public void startReconnect() {
         scheduler = Executors.newSingleThreadScheduledExecutor();
         scheduler.scheduleAtFixedRate(new Runnable() {
             public void run() {
                 if (!client.isConnected()) {
                     try {
                         client.connect(options);
                     } catch (MqttSecurityException e) {
                         e.printStackTrace();
                     } catch (MqttException e) {
                         e.printStackTrace();
                     }
                 }
             }
         }, 0 * 1000, 10 * 1000, TimeUnit.MILLISECONDS);
     }

     private void start() {
         try {
             // host为主机名，test为clientid即连接MQTT的客户端ID，一般以客户端唯一标识符表示，MemoryPersistence设置clientid的保存形式，默认为以内存保存
             client = new MqttClient(HOST, clientid, new MemoryPersistence());
             // MQTT的连接设置
             options = new MqttConnectOptions();
             // 设置是否清空session,这里如果设置为false表示服务器会保留客户端的连接记录，这里设置为true表示每次连接到服务器都以新的身份连接
             options.setCleanSession(true);
             // 设置连接的用户名
             options.setUserName(userName);
             // 设置连接的密码
             options.setPassword(passWord.toCharArray());
             // 设置超时时间 单位为秒
             options.setConnectionTimeout(10);
             // 设置会话心跳时间 单位为秒 服务器会每隔1.5*20秒的时间向客户端发送个消息判断客户端是否在线，但这个方法并没有重连的机制
             options.setKeepAliveInterval(20);
             // 设置回调
             client.setCallback(new PushCallback());
             MqttTopic topic = client.getTopic(TOPIC);
             //setWill方法，如果项目中需要知道客户端是否掉线可以调用该方法。设置最终端口的通知消息
             options.setWill(topic, "close".getBytes(), 0, true);

             client.connect(options);
             //订阅消息
             int[] Qos  = {1};
             String[] topic1 = {TOPIC};
             client.subscribe(topic1, Qos);
         } catch (Exception e) {
             e.printStackTrace();
         }
     }
     public void disconnect() {
          try {
             client.disconnect();
         } catch (MqttException e) {
             e.printStackTrace();
         }
     }



     public static void main(String[] args) throws MqttException {
         Client client = new Client();
         client.start();
     }

 }

Android手机客户端实现demo：

https://github.com/dobermai/android-mqtt-push