pom依赖

        <dependency>
            <groupId>org.eclipse.paho</groupId>
            <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
            <version>1.2.0</version>
        </dependency>

发布端

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.MqttMessage;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

/**
 *发布端
 */
public class PublishSample {
    public static void main(String[] args) {

        String topic = "mqtt/test";
        String content = "hello 哈哈";
        int qos = 1;
        String broker = "tcp://iot.eclipse.org:1883";
        String userName = "test";
        String password = "test";
        String clientId = "pubClient";
        // 内存存储
        MemoryPersistence persistence = new MemoryPersistence();

        try {
            // 创建客户端
            MqttClient sampleClient = new MqttClient(broker, clientId, persistence);
            // 创建链接参数
            MqttConnectOptions connOpts = new MqttConnectOptions();
            // 在重新启动和重新连接时记住状态
            connOpts.setCleanSession(false);
            // 设置连接的用户名
            connOpts.setUserName(userName);
            connOpts.setPassword(password.toCharArray());
            // 建立连接
            sampleClient.connect(connOpts);
            // 创建消息
            MqttMessage message = new MqttMessage(content.getBytes());
            // 设置消息的服务质量
            message.setQos(qos);
            // 发布消息
            sampleClient.publish(topic, message);
            // 断开连接
            sampleClient.disconnect();
            // 关闭客户端
            sampleClient.close();
        } catch (MqttException me) {
            System.out.println("reason " + me.getReasonCode());
            System.out.println("msg " + me.getMessage());
            System.out.println("loc " + me.getLocalizedMessage());
            System.out.println("cause " + me.getCause());
            System.out.println("excep " + me);
            me.printStackTrace();
        }
    }
}

订阅端

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

/**
 *订阅端
 */
public class SubscribeSample {

    public static void main(String[] args) throws MqttException {
        String HOST = "tcp://testiot.zam.com";
        String TOPIC = "test1";
        String TOPIC2 = "test2";
        int qos = 1;
        String clientid = "88daba96-118f-4eff-8dc7-23f3d50fcdad";
        String userName = "admin";
        String passWord = "123456";
        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
            MqttClient client = new MqttClient(HOST, clientid, new MemoryPersistence());
            // MQTT的连接设置
            MqttConnectOptions 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);
            // 设置回调函数
            client.setCallback(new MqttCallback() {

                @Override
                public void connectionLost(Throwable cause) {
                    System.out.println("connectionLost");
                }

                @Override
                public void messageArrived(String topic, MqttMessage message) throws Exception {
                    System.out.println("topic:"+topic);
                    System.out.println("Qos:"+message.getQos());
                    System.out.println("message content:"+new String(message.getPayload()));
                }

                @Override
                public void deliveryComplete(IMqttDeliveryToken token) {
                    System.out.println("deliveryComplete---------"+ token.isComplete());
                }

            });
            client.connect(options);
            //订阅消息
            client.subscribe(TOPIC, qos);
            client.subscribe(TOPIC2, qos);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}