Spring Boot Integration MQTT DSL - Channel not Autowired

Question

I will Spring Boot MQTT Integration with JAVA DSL Configuration. To publish a message I would like to use the MessageHandler as defined

@Slf4j
@Configuration
@EnableIntegration
public class MqttJavaApplicationConfig {

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

    @Bean
    public IntegrationFlow mqttOutFlow() {
        Mqttv5PahoMessageHandler messageHandler = new Mqttv5PahoMessageHandler(brokerUrl, "mqttv5SIout");
        MqttHeaderMapper mqttHeaderMapper = new MqttHeaderMapper();
        mqttHeaderMapper.setOutboundHeaderNames("some_user_header", MessageHeaders.CONTENT_TYPE);
        messageHandler.setHeaderMapper(mqttHeaderMapper);
        messageHandler.setAsync(true);
        messageHandler.setAsyncEvents(true);
        messageHandler.setDefaultTopic("testTopic");

        return f -> f.handle(messageHandler);
    }
}

What is working is to define the MessageGateway

@MessagingGateway
public interface MqttProduceGateway {

    @Gateway(requestChannel = "mqttOutFlow.input")
    void publishToMQTT(String data);
}

autowire the gateway bean

@Getter
@Setter
@NoArgsConstructor
@Component
public class PublishService {

    @Autowired
    MqttProduceGateway mqttProduceGateway;
    

    public boolean publishToMqttBroker(String data){
        mqttProduceGateway.publishToMQTT(data);
        return  true;
    }

}

and send message within my app.

But to keep it as simple as possible, I prefer to use the Message Handler directly, like

@Slf4j
@ComponentScan(basePackages = { "de.diag.testprototypes.projectscv.mqtt.client"})
@IntegrationComponentScan
@SpringBootApplication
public class MqttJavaApplication {

    @Autowired
    @Qualifier("mqttOutFlow.input")
    private DirectChannel mqttOutFlowInput;

But in this case autowiring failed

No qualifying bean of type 'org.springframework.integration.channel.DirectChannel' available:

but the bean exists:

Object object =  context.getBean("mqttOutFlow.input");
log.info("type " + object.getClass().getName());
 

2024-02-22T16:21:25.280+01:00 INFO 26304 --- [ main] d.k.d.t.p.m.client.MqttJavaApplication : type org.springframework.integration.channel.DirectChannel

I got this option from the text.

My question is, why autowiring does not work and what is the "best" option publish MQTT Messages via Spring Integration?