How to do split-aggregate in java dsl by invoking another flow? - spring-integration

Question

In the below example, I'm getting [Manoj, Jeeva] as output. But [Hello Manoj, Hello Jeeva] is the expected. Why serviceChnl is NOT giving output to aggregate?
#Bean
public IntegrationFlow sayHelloIntFlow() {
return IntegrationFlows.from("serviceChnl")
.handle(new GenericHandler<String>() {
public Object handle(String payload, Map<String, Object> headers) {
return "Hello " + payload;
}
})
.get();
}
#Bean
public IntegrationFlow splitFlow() {
return IntegrationFlows.from("splitChnl")
.split()
.channel("serviceChnl")
.aggregate()
.handle(new GenericHandler() {
public Object handle(Object payload, Map headers) {
System.out.println(payload);
return null;
}
})
.channel("nullChannel")
.get();
}
#Test
public void test() {
String[] strArr = new String[] {"Manoj", "Jeeva"};
Message msg = MessageBuilder.withPayload(strArr)
.build();
splitChnl.send(msg);
}

Answer 1

I got it now, after split the message, i either do enrich or transform. I should not put it into the channel.
#Bean
public IntegrationFlow splitFlow() {
return IntegrationFlows.from("splitChnl")
.split()
.transform(new HelloTransformer())
.aggregate()
.handle(new ShowOutput<String>())
.channel("nullChannel")
.get();
}

Answer 2

That's correct answer and you can accept it yourself. Your issue was that you misunderstood a bit inter-channel concept. They aren't intended to send messages to the separate flow (also we can do that), but they connect those endpoints in the one flow. They are there anyway, even if you don't declare .channel() there. For the other flow we have .wireTap() and .gateway(). Please, read Spring Integration Reference Manual about <chain> and DSL Manual. There is enough info to not confuse on the development phase...

Answer 3

Below is an example using .gateway to delegate to another flow.
DefaultAggregatingMessageGroupProcessor is used to aggregate the individual Message payloads into a Collection of payloads.
#Bean
IntegrationFlow splitAndDelegate(IntegrationFlow delegateFlow) {
return flowDef -> flowDef.split()
.gateway(delegateFlow)
.aggregate(aggregatorSpec -> aggregatorSpec.outputProcessor(new DefaultAggregatingMessageGroupProcessor()));
}