apollo-common/src/main/java/com/ctrip/framework/apollo/common/controller/GlobalDefaultExceptionHandler.java/GlobalDefaultExceptionHandler/handleMethodArgumentNotValidException
class GlobalDefaultExceptionHandler:  @ExceptionHandler(MethodArgumentNotValidException.class)
  public ResponseEntity<Map<String, Object>> handleMethodArgumentNotValidException(
      HttpServletRequest request, MethodArgumentNotValidException ex
  ) {
    final Optional<ObjectError> firstError = ex.getBindingResult().getAllErrors().stream().findFirst();
    if (firstError.isPresent()) {
      final String firstErrorMessage = firstError.get().getDefaultMessage();
      return handleError(request, BAD_REQUEST, new BadRequestException(firstErrorMessage));
    }
    return handleError(request, BAD_REQUEST, ex);
  }