Currently, new entity providers were added: java.lang.Boolean, java.lang.Character, java.lang.Number Only for text/plain. Corresponding
primitive types supported via boxing/unboxing conversion.
For the others, the spec. Section 4.2.4 says:
When reading zero-length request entities, all pre-packaged MessageBodyReader implementations except
the JAXB-related one MUST create a corresponding Java object that represents zero-length data;
they MUST NOT return null. The pre-packaged JAXB MessageBodyReader implementation MUST
throw a WebApplicationException with a client error response (HTTP 400) for zero-length request
entities. Moreover, all pre-packaged MessageBodyReader implementations SHOULD throw a Web-
ApplicationException with a client error response (HTTP 400) if any other error is encountered while
reading a request entity.
But for the entities, java objects representing zero length data are not possible to create.