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