如果问题欢迎大佬指正!!!

导包

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

配置MQTT连接信息

mqtt:
  addr: tcp://localhost:1883
  clientId: client_1
  username: admin
  password: public
  keepAlive: 60
  timeout: 60

Mqtt消息回调类

@Component
public class PushCallBack implements MqttCallback {

    @Autowired
    private MqttConfig config;

    @Override
    public void connectionLost(Throwable cause) {
        System.out.println("连接断开");
        MqttPushClient client = config.getMqttPushClient();
        if(client != null){
            client.connect(config.getAddress(),config.getClientId(),config.getUsername(),config.getPassword(),config.getTimeout(),config.getKeepalive());
        }
    }

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

    @Override
    public void deliveryComplete(IMqttDeliveryToken token) {
        System.out.println("消息发送完成");
    }
}

Mqtt发送消息类

@Component
@Data
public class MqttPushClient {

    @Autowired
    private PushCallBack pushCallBack;

    //mqtt连接对象
    private static MqttClient client;

    public static void setClient(MqttClient client) {
        MqttPushClient.client = client;
    }

    public static MqttClient getClient() {
        return client;
    }


    /**
     * 连接mqtt
     * @param host
     * @param clientId
     * @param username
     * @param password
     * @param timeout
     * @param keepalive
     */
    public void connect(String host,String clientId,String username,String password,int timeout,int keepalive){
        MqttClient client;
        try{
            client = new MqttClient(host,clientId);
            MqttConnectOptions options = new MqttConnectOptions();
            options.setUserName(username);
            options.setPassword(password.toCharArray());
            options.setCleanSession(false);
            options.setConnectionTimeout(timeout);
            options.setKeepAliveInterval(keepalive);
            MqttPushClient.setClient(client);
            //设置回调类
            client.setCallback(pushCallBack);
            IMqttToken iMqttToken = client.connectWithResult(options);
            boolean complete = iMqttToken.isComplete();
            System.out.println(complete?"连接成功!":"连接失败！");
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    /**
     * 发送消息
     * @param topic
     * @param msg
     * @param qos
     */
    public void push(String topic,String msg,int qos){
        MqttMessage message = new MqttMessage();
        message.setPayload(msg.getBytes(StandardCharsets.UTF_8));
        message.setQos(qos);
        message.setRetained(false);
        MqttTopic mqttTopic = client.getTopic(topic);
        if (mqttTopic == null){
            System.out.println("主题不存在！");
        }else {
            try {
                client.publish(topic,message);
            } catch (MqttException e) {
                e.printStackTrace();
                System.out.println("消息发送失败！");
            }
        }
    }
}

初始化MqttClient

@Configuration
@Data
public class MqttConfig {

    @Value("${mqtt.addr}")
    private String address;

    @Value("${mqtt.username}")
    private String username;

    @Value("${mqtt.password}")
    private String password;

    @Value("${mqtt.clientId}")
    private String clientId;

    @Value("${mqtt.timeout}")
    private Integer timeout;

    @Value("${mqtt.keepalive}")
    private Integer keepalive;



    @Autowired
    private MqttPushClient mqttPushClient;


//当前类创建好之后，连接MQTT break
    @PostConstruct
    public void mqttInit(){
        mqttPushClient.connect(address,clientId,username,password,timeout,keepalive);
    }
}

测试

@RequestMapping("/mqtt")
@RestController
public class MqttController {

    @Autowired
    private MqttPushClient client;
	
	//发送消息
    @RequestMapping("/send/{msg}")
    public String send(@PathVariable("msg") String msg) throws MqttException {
        client.push("wsl",msg,1);
        return "SUCESS";
    }

	//订阅主题
    @RequestMapping("/sub/{topic}")
    public String subscribe(@PathVariable("topic") String topic) throws MqttException {
        MqttPushClient.getClient().subscribe(topic,1);
        return "SUCESS";
    }
}