Spring Integration: can one call a gateway from within a header enricher? - spring

Question

I need to make a number of calls to gateways and to then place the return payloads into headers. These gateway calls are really sending a message to a channel behind which there is a chain. It currently looks like this:
<int:channel id = "call_api_a" />
<int:chain input-channel = "call_api_a" >
...
</int:chain>
<int:channel id = "call_api_b" />
<int:chain input-channel = "call_api_b" >
...
</int:chain>
<int:gateway request-channel="call_api_a" />
<int:header-enricher>
<int:header name="a" expression="payload" />
</int:header-enricher>
<int:gateway request-channel="call_api_b" />
<int:header-enricher>
<int:header name="b" expression="payload" />
</int:header-enricher>
Is there an elegant way to embed the call to the gateway inside of the header-enricher?
Something like:
<int:header-enricher>
<int:header name="a">
<int:gateway request-channel="call_api_a" />
</int:header>
</int:header-enricher>
I know that the above doesn't work but gives the sense of what I'd like to achieve.
Thanks for any pointers and best regards.
-aljo

Answer 1

Not <gateway>, but like this:
<int:header-enricher>
<int:header name="a" ref="myGateway" method="gatewayMethod"/>
</int:header-enricher>
The <gateway> is bean based on some service interface.
You just point in the <header> definition to that bean and its method to be called against your payload or message.
There is some explanation in the docs: https://docs.spring.io/spring-integration/docs/current/reference/html/message-transformation.html#header-enricher

Answer 2

It looks like the "additional gateway definition" is the way to go on this one. Thanks, #artem-bilan, for pointing me in the right direction.
I want to call to my chain-channel directly from a header-enricher.
If my chain-channel is:
<int:channel id = "call_api_a" />
<int:chain input-channel = "call_api_a" >
...
</int:chain>
Define somewhere in the Java add your gateway interface.
package com.app.wonderful;
#FunctionalInterface
public interface MyChainChannelGatewayMethod {
Message<?> callChainChannel(Message<?> message) throws MessageException;
}
Define a gateway that points to your chain-channel:
<int:gateway default-request-channel = "call_api_a"
id = "call_api_a_GW"
service-interface. = "com.app.wonderful.MyChainChannelGatewayMethod" />
Then you can call your gateway in-line from the SpEL expression in the header-enricher:
<int:header-enricher >
<int:header name="a" expression="#call_api_a_GW(#root).payload" />
</int:header>
Does the trick for me. Thanks again.

Answer 3

#artem-bilan's suggestion to use <enricher> instead of <header-enricher> leads to a solution that obviates the Java interface signatures by addressing directly a channel.
<int:channel id = "call_api_a" />
<int:chain input-channel = "call_api_a" >
...
</int:chain>
We can call this channel from an <enricher>. Here, for simplicity, the <enricher> component is part of a chain, but that is not a requirement:
<int:chain ...>
<int:enricher request-channel="call_api_a"
request-payload-expression="payload" >
<int:header name="a" expression="payload" />
</int:enricher>
</int:chain>
Thanks again for the pointers.