@Override
 public Response toResponse(MethodConstraintViolationException ex) {
   Map<String, String> errors = new HashMap<String, String>();
   for (MethodConstraintViolation<?> methodConstraintViolation : ex.getConstraintViolations()) {
     errors.put(
         methodConstraintViolation.getParameterName(), methodConstraintViolation.getMessage());
   }
   return Response.status(Status.PRECONDITION_FAILED).entity(errors).build();
 }