spring-integration-mqtt 查看是否连接上mqtt服务器 代码

您可以通过 Spring Integration MQTT 提供的 `MqttPahoMessageDrivenChannelAdapter` 组件来检查是否连接到 MQTT 服务器。以下是一个示例：

@Configuration
@EnableIntegration
public class MqttConfiguration {

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

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

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

    @Bean
    public MessageChannel mqttInputChannel() {
        return new DirectChannel();
    }

    @Bean
    public MqttPahoClientFactory mqttClientFactory() {
        DefaultMqttPahoClientFactory factory = new DefaultMqttPahoClientFactory();
        MqttConnectOptions options = new MqttConnectOptions();
        options.setServerURIs(new String[]{brokerUrl});
        factory.setConnectionOptions(options);
        return factory;
    }

    @Bean
    public MessageProducer inbound() {
        MqttPahoMessageDrivenChannelAdapter adapter =
                new MqttPahoMessageDrivenChannelAdapter(clientId, mqttClientFactory(), topic);
        adapter.setCompletionTimeout(5000);
        adapter.setConverter(new DefaultPahoMessageConverter());
        adapter.setQos(1);
        adapter.setOutputChannel(mqttInputChannel());
        return adapter;
    }
    
    @Bean
    public IntegrationFlow mqttInFlow() {
        return IntegrationFlows.from(mqttInputChannel())
                .handle(new MessageHandler() {
                    @Override
                    public void handleMessage(Message<?> message) throws MessagingException {
                        // Handle received message
                    }
                })
                .get();
    }
    
    @Bean
    public ApplicationRunner runner() {
        return args -> {
            MqttPahoClientFactory factory = mqttClientFactory();
            IMqttAsyncClient client = factory.createMqttClient();
            IMqttToken token = client.connect();
            token.waitForCompletion();
            if (token.isComplete() && token.getException() == null) {
                System.out.println("Connected to MQTT broker: " + brokerUrl);
            } else {
                System.out.println("Failed to connect to MQTT broker: " + brokerUrl);
            }
            client.disconnect();
        };
    }

}

在上面的代码中，我们创建了一个 `MqttPahoMessageDrivenChannelAdapter` 对象，并将其配置为连接到 MQTT 服务器、订阅指定的主题，并将收到的消息发送到 `mqttInputChannel` 消息通道。我们还创建了一个 `ApplicationRunner` 对象，在应用程序启动时尝试连接到 MQTT 服务器，并在控制台上输出连接结果。通过查看控制台输出，您可以确定是否成功连接到 MQTT 服务器。