Support of Multiple @StreamListener methods on the same bound element

Hi,

I have a case where I want to have multiple @StreamLinstner methods that are listening on the same bound element. The methods signature are different depending the type of message being received. Here is the example:

@StreamListener(Sink.INPUT)
public void on(PostUpvotedEvent event) {

}

@StreamListener(Sink.INPUT)
public void on(PostDownvotedEvent event) {

}

Currently, this is not supported and there is an exception with this message Duplicate @StreamListener mapping for 'input'.

I think it will be convenient to have this feature. Thanks

[mbogoevici]

Chatting a bit more with @dturanski, here are couple of further refinements to the proposal in cases when more than one condition is met for an incoming message:

• if more than one condition matches, handlers will be executed serially in the same thread (for now, there’s no ordering convention) - at a first error, an exception will be thrown;
• if more than one condition matches at runtime, and at least one of the handlers has a return type, an exception will be thrown - this is in order to prevent side-effects;
• if no condition matches, we will issue a warning - it might be possible to consider adding a fallback mapping for a channel;

[garyrussell]

It’s best to not add comments to closed issues, but open a new issue if you find a problem. Questions should be submitted on Stack Overflow or in gitter.

If you are using the kafka11 binder, headers are supported natively (added to the 0.11.x.x client and above including 1.0.0).

If you are using 1.3.0 or earlier versions of the binder (with the default kafka 0.10.x.x client) you need to tell the binder which header(s) should be transported. See Kafka Binder Properties in the documentation.

spring.cloud.stream.kafka.binder.headers The list of custom headers that will be transported by the binder.

Default: empty.