# MQTT 订阅者项目 - 核心代码总结

## 项目概述
Spring Boot MQTT 订阅者最小可行性验证项目，用于连接 MQTT Broker 并订阅指定 Topic 接收消息数据。

## 技术栈
- Eclipse Paho MQTT 1.2.5
- dotenv-java 3.2.0


## 2. application.yaml

```yaml
mqtt:
  broker: ${MQTT_BROKER:tcp://10.0.0.202:8082}
  client-id: ${MQTT_CLIENT_ID:springboot-mqtt-client}
  username: ${MQTT_USERNAME:mqtt}
  password: ${MQTT_PASSWORD:XAsOsLxaPs1}
  topic: ${MQTT_TOPIC:test/topic}
  timeout: ${MQTT_TIMEOUT:30}
  keepalive: ${MQTT_KEEPALIVE:60}
```

## 4. MqttConfig.java

```java
package com.example.demo.config;

import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MqttConfig {

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

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

    @Value("${mqtt.timeout:30}")
    private int timeout;

    @Value("${mqtt.keepalive:60}")
    private int keepalive;

    @Bean
    public MqttConnectOptions mqttConnectOptions() {
        MqttConnectOptions options = new MqttConnectOptions();
        options.setCleanSession(true);
        options.setConnectionTimeout(timeout);
        options.setKeepAliveInterval(keepalive);

        if (username != null && !username.isEmpty()) {
            options.setUserName(username);
            options.setPassword(password.toCharArray());
        }

        return options;
    }
}
```

---

## 5. MqttSubscriber.java

```java
package com.example.demo.subscriber;

import jakarta.annotation.PostConstruct;
import org.eclipse.paho.client.mqttv3.*;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import java.nio.charset.StandardCharsets;

@Component
public class MqttSubscriber {

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

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

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

    private final MqttConnectOptions options;

    public MqttSubscriber(MqttConnectOptions options) {
        this.options = options;
    }

    @PostConstruct
    public void init() throws MqttException {
        MqttClient client = new MqttClient(broker, clientId);

        client.setCallback(new MqttCallback() {
            @Override
            public void connectionLost(Throwable cause) {
                System.out.println("❌ MQTT 连接断开：" + cause.getMessage());
            }

            @Override
            public void messageArrived(String topic, MqttMessage message) {
                String payload = new String(message.getPayload(), StandardCharsets.UTF_8);
                System.out.println("📥 收到消息");
                System.out.println("Topic: " + topic);
                System.out.println("Payload: " + payload);
            }

            @Override
            public void deliveryComplete(IMqttDeliveryToken token) {
            }
        });

        client.connect(options);
        client.subscribe(topic, 0);

        System.out.println("✅ MQTT 已连接，订阅 Topic：" + topic);
    }
}
```