java连接MQTT服务器(Springboot+gradle整合MQTT)

要在Spring Boot项目中使用MQTT，你需要引入以下依赖：

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation 'org.springframework.integration:spring-integration-mqtt'
    implementation 'org.eclipse.paho:org.eclipse.paho.client.mqttv3'
}

然后在application.properties文件中配置MQTT服务器连接信息：

spring.mqtt.broker-url=tcp://localhost:1883
spring.mqtt.username=username
spring.mqtt.password=password

接下来，你需要创建一个MQTT消息处理器类：

@Component
public class MqttMessageHandler {

    @ServiceActivator(inputChannel = "mqttInputChannel")
    public void handleMessage(String message) {
        System.out.println("Received message: " + message);
    }

}

最后，你需要在Spring Boot应用程序中配置MQTT消息通道：

@Configuration
@EnableIntegration
public class MqttConfig {

    private static final String MQTT_CLIENT_ID = "mqtt-client";

    @Value("${spring.mqtt.broker-url}")
    private String brokerUrl;

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

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

    @Bean
    public MqttPahoClientFactory mqttClientFactory() {
        DefaultMqttPahoClientFactory factory = new DefaultMqttPahoClientFactory();
        MqttConnectOptions options = new MqttConnectOptions();
        options.setServerURIs(new String[]{brokerUrl});
        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(MQTT_CLIENT_ID, mqttClientFactory(), "test-topic");
        adapter.setCompletionTimeout(5000);
        adapter.setConverter(new DefaultPahoMessageConverter());
        adapter.setQos(1);
        adapter.setOutputChannel(mqttInputChannel());
        return adapter;
    }

}

这里我们配置了一个名为test-topic的主题，用来接收MQTT消息。当有消息到达时，它将被传递到mqttInputChannel通道，然后被MqttMessageHandler处理。