jaxrs 2.1 spec says:
In a product that supports the Java API for JSON Processing (JSON-P) [18], implementations MUST support
entity providers for JsonValue and all of its sub-types: JsonStructure , JsonObject , JsonArray ,
JsonString and JsonNumber .

We should add provider for JsonSring and JsonNumber and read/write this type argument and return like :

@Path("number")
@POST
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public JsonNumber testNumber(JsonNumber number)

{ return Json.createValue(number.intValue() + 100); }

@Path("string")
@POST
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public JsonString testString(JsonString string)

{ return Json.createValue("Hello " + string.getString()); }