Код

@Slf4j

@RestControllerAdvice

public class GlobalExceptionController {

  @ExceptionHandler(UserNotFoundException.class)

  @ResponseStatus(HttpStatus.NOT_FOUND)

  public Mono handleUserNotFoundException(Exception ex) {

    return Mono.just(new ErrorDto(ex.getMessage()));

  }

  @ExceptionHandler({UserAlreadyExistsException.class})

  @ResponseStatus(HttpStatus.NOT_ACCEPTABLE)

  public Mono handleUserAlreadyExistsException(Exception ex) {

    return Mono.just(new ErrorDto(ex.getMessage()));

  }

}