Allow a single action method to support multiple request content types

[mmihic]

Currently action methods can only support a single request content type, and content negotiation picks actions based on the incoming content type. We should allow actions to support multiple request content types; this would allow a single action to support both json and protobuf for wire messages, for example.

[swankjesse]

Tough problem. I think this is equivalent to image formats: application layer can serve PNGs and interceptors can convert to GIFS or JPGS for the client’s benefit.

I wonder if we should take that approach – get the application layer to work in protos, and for interceptors or other mechanism to automatically convert. That might be easier.

[tso]

This is somewhat done (perhaps entirely?) with #85

[mmihic]

#85 is different - it allows us to pick between two actions that map to the same path based on requested content type. This issue is to allow a single action to support multiple content types that map to the same Java type representation, and to have the interceptor or marshalling framework convert to the appropriate wire format based on the content type that was requested.

[MartinHorsfieldFaire]

I am working on a similar problem right now, what is the best approach to support multiple content types from a single action currently?