中间件：SpringBoot-JAVA整合MQTT通信

在Spring Boot中整合MQTT通信，可以使用spring-integration-mqtt库。以下是一个简单的例子，展示如何在Spring Boot应用程序中配置MQTT客户端并接收消息。

1. 添加依赖到pom.xml：

<dependencies>
    <!-- Spring Boot Web Starter -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
 
    <!-- Spring Integration MQTT -->
    <dependency>
        <groupId>org.springframework.integration</groupId>
        <artifactId>spring-integration-mqtt</artifactId>
    </dependency>
</dependencies>

2. 配置MQTT客户端在application.properties或application.yml：

# MQTT Broker Configuration
spring.mqtt.username=
spring.mqtt.password=
spring.mqtt.url=tcp://localhost:1883
spring.mqtt.client.client-id=clientId
spring.mqtt.default.topic=testTopic

3. 配置MQTT消息的接收和发送：

@Configuration
@IntegrationComponentScan
public class MqttConfig {
 
    @Value("${spring.mqtt.url}")
    private String url;
 
    @Value("${spring.mqtt.client.client-id}")
    private String clientId;
 
    @Value("${spring.mqtt.username}")
    private String userName;
 
    @Value("${spring.mqtt.password}")
    private String password;
 
    @Value("${spring.mqtt.default.topic}")
    private String defaultTopic;
 
    @Bean
    public MqttPahoClientFactory mqttClientFactory() {
        DefaultMqttPahoClientFactory factory = new DefaultMqttPahoClientFactory();
        MqttConnectOptions options = new MqttConnectOptions();
        options.setServerURIs(new String[]{url});
        options.setUserName(userName);
        options.setPassword(password.toCharArray());
        factory.setConnectionOptions(options);
        return factory;
    }
 
    @Bean
    public MessageChannel mqttInputChannel() {
        return new DirectChannel();
    }
 
    @Bean
    public MessageProducer inbound() {
        MqttPahoMessageDrivenChannelAdapter adapter =
                new MqttPahoMessageDrivenChannelAdapter(clientId, mqttClientFactory(), defaultTopic);
        adapter.setQos(1);
        adapter.setOutputChannel(mqttInputChannel());
        return adapter;
    }
 
    @Bean
    @ServiceActivator(inputChannel = "mqttInputChannel")
    public MessageHandler handler() {
        return message -> {
            MqttMessage mqttMessage = (MqttMessage) message.getPayload();
            String payload = new String(mqttMessage.getPayload(), StandardCharsets.UTF_8);