Java 连接MQTT

<dependency>
            <groupId>org.eclipse.paho</groupId>
            <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
            <version>1.2.2</version>
</dependency>

1.模拟客户端接收消息

import java.util.concurrent.ScheduledExecutorService;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttTopic;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
 
/**
 * 模拟一个客户端接收消息
 *
 * @author Unclue_liu
 */
public class ClientMQTT {
 
    public static final String HOST = "tcp://192.168.1.77:1883";
    public static final String TOPIC1 = "pos_message_all";
    private static final String clientid = "12345678";
    private MqttClient client;
    private MqttConnectOptions options;
    private String userName = "mqtt";    //非必须
    private String passWord = "mqtt";  //非必须
    private ScheduledExecutorService scheduler;
 
    private void start() {
        try {
            // host为主机名，clientid即连接MQTT的客户端ID，一般以唯一标识符表示，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，设置为true表示每次连接到服务器都以新的身份连接
            options.setCleanSession(false);
            // 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);
            //设置断开后重新连接
            options.setAutomaticReconnect(true);
            // 设置回调
            client.setCallback(new PushCallback());
            MqttTopic topic = client.getTopic(TOPIC1);
            //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
            //遗嘱
            options.setWill(topic, "close".getBytes(), 1, true);
            client.connect(options);
            //订阅消息
            int[] Qos = {1};//0：最多一次 、1：最少一次 、2：只有一次
            String[] topic1 = {TOPIC1};
            client.subscribe(topic1, Qos);
 
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
    public static void main(String[] args)  {
        ClientMQTT client = new ClientMQTT();
        client.start();
 
    }

2.模拟服务端发送消息

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.persist.MemoryPersistence;
/**
 * Title:Server 这是发送消息的服务端
 * Description: 服务器向多个客户端推送主题，即不同客户端可向服务器订阅相同主题
 * @author Unclue_liu
 */
public class ServerMQTT {
 
    //tcp://MQTT安装的服务器地址:MQTT定义的端口号
    public static final String HOST = "tcp://192.168.1.77:1883";
    //定义一个主题
    public static final String TOPIC = "pos_message_all";
    //定义MQTT的ID，可以在MQTT服务配置中指定
    private static final String clientid = "server11";
 
    private MqttClient client;
    private static MqttTopic topic11;
//    private String userName = "mqtt";  //非必须
//    private String passWord = "mqtt";  //非必须
 
    private static MqttMessage message;
 
    /**
     * 构造函数
     * @throws MqttException
     */
    public ServerMQTT() 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();
    }
 
    /**
     *  用来连接服务器
     */
    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);
            topic11 = client.getTopic(TOPIC);
 
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
    /**
     *
     * @param topic
     * @param message
     * @throws MqttPersistenceException
     * @throws MqttException
     */
    public static void publish(MqttTopic topic , MqttMessage message) throws MqttPersistenceException,
            MqttException {
        MqttDeliveryToken token = topic.publish(message);
 
        token.waitForCompletion();
        System.out.println("message is published completely! "
                + token.isComplete());
    }
 
 
    public static void sendMessage(String clieId,String msg)throws Exception{
        ServerMQTT server = new ServerMQTT();
        server.message = new MqttMessage();
        server.message.setQos(1);  //保证消息能到达一次
        server.message.setRetained(true);
        String str ="{\"clieId\":\""+clieId+"\",\"mag\":\""+msg+"\"}";
        server.message.setPayload(str.getBytes());
        try{
            publish(server.topic11 , server.message);
            //断开连接
//            server.client.disconnect();
        }catch (Exception e){
            e.printStackTrace();
        }
 
    }
    /**
     *  启动入口
     * @param args
     * @throws MqttException
     */
    public static void main(String[] args) throws Exception {
        sendMessage("123444","哈哈");
    }
}

3.发布消息回调类

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttMessage;
 
/**
 * 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(IMqttDeliveryToken token) {
        System.out.println("deliveryComplete---------" + token.isComplete());
    }
 
    public void messageArrived(String 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);
        System.out.println("接收消息Qos : " + message.getQos());
        System.out.println("接收消息内容 : " + new String(message.getPayload()));
    }
}