CODEWITHSUNDEEP
springapache-kafkaspring-integrationspring-cloudspring-cloud-stream
user26270
user26270

Reputation: 7084

why does spring cloud stream's @InboundChannelAdapter accept no parameters?

I'm trying to use spring cloud stream to send and receive messages on kafka. The examples for this use a simple example of using time stamps as the messages. I'm trying to go just one step further into a real world application when I ran into this blocker on the InboundChannelAdapter docs:

"A method annotated with @InboundChannelAdapter can't accept any parameters"

I was trying to use it like so:

@InboundChannelAdapter(value = ChannelManager.OUTPUT)
public EventCreated createCustomerEvent(String customerId, String thingId) {
    return new EventCreated(customerId, thingId);
}

What usage am I missing? I imagine that when you want to create an event, you have some data that you want to use for that event, and so you would normally pass that data in via parameters. But "A method annotated with @InboundChannelAdapter can't accept any parameters". So how are you supposed to use this?

I understand that @InboundChannelAdapter comes from spring-integration, which spring-cloud-stream extends, and so spring-integration may have a different context in which this makes sense. But it seems un-intuitive to me (as does using an _INBOUND_ChannelAdapter for an output/producer/source)

Upvotes: 0

Views: 644

Answers (2)

Vinicius Carvalho
Vinicius Carvalho

Reputation: 4156

How are you expecting to call that method? I think there was a miscommunication with your statement "stream extends integration" and Artem probably understood that we extend @InboundChannelAdatper

So, if you are actively calling this method, as it appears since you do have arguments that are passed to it, why not just using your source channel to send the data?

Usually sources do not require arguments as they are either push like the twitter stream that taps on twitter, listen for events and pushes them to the source channel, or they are polled, in which case, they are invoked on an interval defined via a poller.

As Artem pointed, if your intention is to call this method from your business flow, and deal with the return while triggering a message flow, then check his link from the docs.

Upvotes: 1

Artem Bilan
Artem Bilan

Reputation: 121552

Well, first of all the @InboundChannelAdapter is defined exactly in Spring Integration and Spring Cloud Stream doesn't extend it. That's false. Not sure where you have picked up that info...

This annotation builds something like SourcePollingChannelAdapter which provides a poller based on the scheduler and calls periodically a MessageSource.receive(). Since there is no any context and end-user can't effect that poller's behavior with his own arguments, the requirement for empty method parameters is obvious.

This @InboundChannelAdapter is a beginning of the flow and it is active. It does its logic on background without your events.

If you would like to call some method with parameters and trigger with that some flow, you should consider to use @MessagingGateway: http://docs.spring.io/spring-integration/reference/html/messaging-endpoints-chapter.html#messaging-gateway-annotation

Upvotes: 2

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