MessageBodyReader and Writer are used in various contexts. For example, on server side, Reader is used to read request body. On the client side, Reader is used to read response body. Writer is the same case as Reader, they do alway read message body, but there is no guarantee that it is going to be request or response.

Also, this mailing list is no longer used, JAX-RS has been moved under Eclipse foundation, please see https://projects.eclipse.org/projects/ee4j.jaxrs.

Regards,
Pavel