Java通过MQTT协议对接第三方设备————够用但不详细

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;
 
public class MqttPublishClient {
    private MqttClient mqttClient;
    private String broker;
    private int qos;
    private String topic;
    private String userName;
    private String password;
 
    public MqttPublishClient(String broker, int qos, String topic, String userName, String password) throws MqttException {
        this.broker = broker;
        this.qos = qos;
        this.topic = topic;
        this.userName = userName;
        this.password = password;
 
        initializeClient();
    }
 
    private void initializeClient() throws MqttException {
        String clientId = MqttClient.generateClientId();
        mqttClient = new MqttClient(broker, clientId, new MemoryPersistence());
        MqttConnectOptions connOpts = new MqttConnectOptions();
        connOpts.setCleanSession(true);
        connOpts.setUserName(userName);
        connOpts.setPassword(password.toCharArray());
 
        mqttClient.connect(connOpts);
    }
 
    public void publishMessage(String message) throws MqttException {
        MqttMessage mqttMessage = new MqttMessage(message.getBytes());
        mqttMessage.setQos(qos);
 
        mqttClient.publish(topic, mqttMessage);
    }
 
    public void disconnect() throws MqttException {
        if (mqttClient.isConnected()) {
            mqttClient.disconnect();
        }
    }
 
    public static void main(String[] args) {
        try {
            MqttPublishClient publisher = new MqttPublishClient("tcp://broker.hivemq.com", 2, "test/topic", "user", "pass");
            publisher.publishMessage("Hello MQTT");
            publisher.disconnect();
        } catch (MqttException e) {
            e.printStackTrace();
        }
    }
}

这段代码展示了如何使用Eclipse Paho客户端库创建一个MQTT客户端，连接到一个MQTT代理，并发布一条消息。这个例子使用了HiveMQ的公共代理，并设置了清理会话和用户认证。在实际应用中，你需要替换代理地址、用户认证信息以及主题名，并根据自己的需求调整服务质量(QoS)。