How to log SpringBoot request validation errors?

How to log request validation errors in springboot? Say, we have an API like below and I need to log if there's a validation error in one of the request params?

@GetMapping(value = "/hello", produces = MediaType.APPLICATION_JSON_VALUE)
    public String sayHi(@RequestParam(name = "size") @Max(30) Integer size) {
      return "Hi" + size.toString();
}

If the size value is more than 30 then the API returns a validation error. But, along with that, I'm also looking for a way to log such invalid requests

Since you are using springboot , you could use spring boot centralized exception handling using @ControllerAdvice to log these errors or return a custom common response class . The @ControllerAdvice annotation will make it apply globally to all controllers.
In order to catch validation errors for request bodies , we will handle MethodArgumentNotValidExceptions like:

@ControllerAdvice
class ErrorHandlingControllerAdvice {

  private static final Logger LOGGER = LoggerFactory.getLogger(ErrorHandlingControllerAdvice.class);
  @ExceptionHandler(ConstraintViolationException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  @ResponseBody
  ApiErrorResponse onConstraintValidationException(
      ConstraintViolationException e) {
    ApiErrorResponse apiErrorResponse = new ApiErrorResponse();
    for (ConstraintViolation violation : e.getConstraintViolations()) {
      apiErrorResponse.getViolations().add(
        new Violation(violation.getPropertyPath().toString(), violation.getMessage()));
    }
    return apiErrorResponse;
  }

  @ExceptionHandler(MethodArgumentNotValidException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  @ResponseBody
  ApiErrorResponse onMethodArgumentNotValidException(
      MethodArgumentNotValidException e) {
    ApiErrorResponse error = new ApiErrorResponse();
    for (FieldError fieldError : e.getBindingResult().getFieldErrors()) {
      error.getViolations().add(
        new Violation(fieldError.getField(), fieldError.getDefaultMessage()));
    }
    LOGGER.error("Log whatever you want to here");
    return error;
  }

}