春季从MQTT出站通道适配器获取事件

Question

I am already using the Spring Integration 4.1.0 SNAPSHOT.

I have this MQTT outbound adapter:

<int-mqtt:outbound-channel-adapter
        async="true"
        async-events="true"
        id="mqttOutput"
        channel="httpInputChannel"
        client-id="#{controller.mqttPublisherConfig.clientID}"
        url="#{controller.mqttPublisherConfig.completeURL}"
        default-qos="#{controller.mqttPublisherConfig.qosString}"
        default-retained="#{controller.mqttPublisherConfig.retainFlag}"
        default-topic="#{controller.mqttPublisherConfig.topic}"
        />

Now in my Controller (MVC app), I want to receive the events emitted by the adapter.

I am implementing ApplicatinListener:

    @Controller
    public class ServletController implements ApplicationListener {

        public void onApplicationEvent(ApplicationEvent event)
        {
         //
        }

        ...
    }

Still , I am not receiving any events from the MQTT adapter.

Implementing an in-event:inbound-channel-adapter works, though:

<int-event:inbound-channel-adapter channel="eventLogger" 
                               error-channel="eventErrorChannel"
                               />

But I would really like to handle the events in the code!

Answer 1

Is your @Controller in the same application context as the MQTT adapter? Or (as is most common), the controller is in the web ( DispatcherServlet 's) context and the other beans are in the root application context loaded by the ContextLoaderListener .

The problem is beans in the root context cannot "see" beans in the servlet context and events published in the root context are not received by listeners in the child context.

You would have to subvert this visibility issue - either move the business beans into the web context (not generally recommended, but not terrible for a small application) or somehow wire a listener from the root context into the controller - perhaps by wiring it into the controller and have the controller pass itself into the listener during initialization ( afterPropertiesSet() ). You'd have a class tangle (mutual dependency), but it should work.

By the way, ApplicationListener can take generics so

public class MyListener implements ApplicationListener<MqttIntegrationEvent> { ... }

will only get MQTT events.

EDIT:

Another solution would be to use the event channel adapter and add an outbound-channel-adapter to the web context (the same context as the controller)...

@Controller
...

    public void onMqttEvent(MqttIntegrationEvent event) { ... }


<int:outbound-channel-adapter channel="eventLogger"
    ref="myController" method="onMqttEvent" />

It will have visibility to the channel in the root context.

Be sure to configure the event adapter to only receive MqttIntegrationEvent s.