Example uses of both Refit (.NET) and Retrofit (Java).
You'll find the same 'Hello World' example implemented with both libraries. This sample invokes the GitHub Markdown API, passing-it a string and retrieves the translated HTML.
Note that, in this API, the request body is Json whereas the response is a raw string. In the Java case, there's a trick to apply to prevent Retrofit from trying to parse the response as Json: one must return a ResponseBody object instead of a String. Thanks @devnied for providing the solution.