Java通过MQTT订阅主题为xxx步骤代码

桃扇骨 2024-03-16 19:13 85阅读 0赞

![208f3d0247557eacabe956c60c8438ca.png_pic_center][]

要通过MQTT订阅主题为xxx步骤，可以使用以下示例代码：

import org.eclipse.paho.client.mqttv3.*;
    import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
    
    public class MqttSubscribeExample {
    
        public static void main(String[] args) {
    
            String broker = "tcp://mqtt.eclipseprojects.io:1883";
            String clientId = "JavaMqttClient";
            String topic = "主题";
    
            try {
                // 创建一个MQTT客户端
                MqttClient mqttClient = new MqttClient(broker, clientId, new MemoryPersistence());
    
                // 创建连接选项
                MqttConnectOptions connOpts = new MqttConnectOptions();
                connOpts.setCleanSession(true);
    
                // 连接到MQTT服务器
                System.out.println("Connecting to broker: " + broker);
                mqttClient.connect(connOpts);
                System.out.println("Connected");
    
                // 创建订阅回调
                mqttClient.setCallback(new MqttCallback() {
                    @Override
                    public void connectionLost(Throwable cause) {
                        System.out.println("Connection lost");
                    }
    
                    @Override
                    public void messageArrived(String topic, MqttMessage message) throws Exception {
                        System.out.println("Message arrived: " + topic + " " + message);
                    }
    
                    @Override
                    public void deliveryComplete(IMqttDeliveryToken token) {
                        System.out.println("Delivery complete");
                    }
                });
    
                // 订阅主题
                mqttClient.subscribe(topic);
                System.out.println("Subscribed to topic: " + topic);
    
            } catch (MqttException e) {
                e.printStackTrace();
            }
        }
    }

这将使用Paho MQTT库订阅 xxx 主题。当收到新消息时，`messageArrived` 方法将会被调用并输出接收到的消息。请注意，您需要将 `broker` 变量的值替换为您要连接的MQTT服务器地址。

[208f3d0247557eacabe956c60c8438ca.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/fb7ee1fe4b7640a083b591c8d2191077.png