I have found some code about the initialization of the HandlerMethodReturnValueHandler.
It uses a custom InitializingBean an the EtagHeaderResultReturnValueHandler wraps two
HandlerMethodReturnValueHandler from the RequestMappingHandlerAdapter.


private HandlerMethodReturnValueHandler wrap(HandlerMethodReturnValueHandler handler) {
if (handler instanceof RequestResponseBodyMethodProcessor
|| handler instanceof RepresentationModelProcessorHandlerMethodReturnValueHandler) {
return new EtagHeaderResultReturnValueHandler(handler);
}
return handler;
}


Hope this helps.

I am sorry but there is no puplic repository where you have access to the source code.
Registering the custom HandlerMethodReturnValueHandler was/is tricky.
As far as I remember, you have to use the RequestMappingHandlerAdapter and get the List of all HandlerMethodReturnValueHandler and inject the custom one at a appropiate place.
But I will look throw my private repositories for further information.

Greetings Lucca