// pseudo-java code
@Path("/orders")
OrderResource {
   OrderV1Impl v1Impl;
   OrderV2Impl v2Impl;
   @GET
   public List<Order> findAll(@HeaderParam header) {
       version = header.get("accepts")
       if(version.equals("v1")) { return v1Impl.findAll() }
       else if(version.equals("v2")) { return v2Impl.findAll() }
       return error
   }
}