Spring boot REST validation error response

You should create a class that use @ControllerAdvice and extends ResponseEntityExceptionHandler. Then you can override the method handleMethodArgumentNotValid. You can use something like that:

@ControllerAdvice
public class RestResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {

@Override
@ResponseStatus(HttpStatus.BAD_REQUEST)
protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
    final List<FieldError> fieldErrors = ex.getBindingResult().getFieldErrors();
    Map <String, Set<String>> errorsMap =  fieldErrors.stream().collect(
            Collectors.groupingBy(FieldError::getField,
                    Collectors.mapping(FieldError::getDefaultMessage, Collectors.toSet())
            )
    );
    return new ResponseEntity(errorsMap.isEmpty()? ex:errorsMap, headers, status);
    }
}