Add Multi-input Bridge

[garyrussell]

Perhaps

@BridgeFrom({ channels = "foo", "bar", "*.baz.*" })
@Bean
public MessageChannel out() {
    ...
}

and create multiple bridges.

See spring-cloud/spring-cloud-stream#1582 for one use case.

Also consider adding @Repeatable(BridgesFrom.class) to @BridgeFrom

[garyrussell]

Pattern(s) might be tricky unless we move annotation processing to later in the context lifecycle; we can't getBeansOfType in a BPP.

[artembilan]

Sounds like we need to think about MultiInputConsumerEndpoint or CompositeIntegrationConsumer to support several input channels including patterns.

In the past, when I developed applications using Spring Integration, I also thought why there is no fan-in support when we would like to dump several channels to a single one...
Doesn't sound like should be as a general feature, but at least the bridge capabilities...

[artembilan]

Seems for me we end up with the replyChannel header population in the end of each flow. I mean the @BridgeTo with upstream HeaderEnricher does the required trick.

Although i don't mind to go ahead with proposed feature to avoid even that boilerplate code. 😄

[garyrussell]

MultiInputChannel consumer PoC here... garyrussell@e10722d

[artembilan]

Yeah... The problem is that you don't support PollableChannel and ReactiveStreamsSubscribableChannel over there.
That's why I thought about CompositeIntegrationConsumer instead. Where every channel will get its own endpoint.

But we can continue to play.
Thank you for cracking this one!

[garyrussell]

I am trying to avoid too much work in the annotation BPP - if we want to support patterns then we can't resolve channels early.

But, yes, some kind of wrapper around the existing consumers should work.

[artembilan]

While it is still hot in mind mind I would like to share it.
Another way to achieve a request is like @Repeatable hint:

@BridgeFrom("channel1")
@BridgeFrom(value = "channel2", poller = @Poller)

Similar trick we should apply for all the Messaging annotations.
I even believe that we don't need to modify anything in the MessagingAnnotationPostProcessor.

Might be as a separate issue though, since this one is more about pattern matching support and composite endpoint.

[garyrussell]

Yes; I included that in the original description 😄

Also consider adding @Repeatable(BridgesFrom.class) to @BridgeFrom

But, yes, it could apply to all.

[artembilan]

The same concept must be applied for the @StreamListener in the Spring Cloud Stream: https://stackoverflow.com/questions/54573861/spring-cloud-stream-how-to-specify-single-message-handler-for-a-set-of-bindings