如何通过Spring-boot从MQTT协议的代理接收消息？

Question

我对MQTT协议感兴趣，我已经知道Web后端的基本知识但又很新。因此，我想知道如何接收来自经纪人的消息。 这是我正在尝试的代码：

public class mqttHelper {

public IMqttClient publisher;
public String hostAddress;
public int port =1883;
public String publisherId = UUID.randomUUID().toString();

public mqttHelper(String hostAddress, int port) throws MqttException {
    this.hostAddress=hostAddress;
    this.port=port;
    publisher= new MqttClient(hostAddress+':'+port,publisherId);

    MqttConnectOptions options = new MqttConnectOptions();
    options.setAutomaticReconnect(true);
    options.setCleanSession(true);
    options.setConnectionTimeout(10);
    publisher.connect(options);


    /*
    //For receiving messages:
    CountDownLatch receivedSignal = new CountDownLatch(10);
    subscriber.subscribe(EngineTemperatureSensor.TOPIC, (topic, msg) -> {
        byte[] payload = msg.getPayload();
        // ... payload handling omitted
        receivedSignal.countDown();
    });
    receivedSignal.await(1, TimeUnit.MINUTES);

    */


}