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