Java objects validation in spring without annotations

Question

I'm working with mybatis to perform all database actions. I'm also working with an Angular front-end, so the validations in the client are made with angular-validation-ghiscoding and the native HTML5 validations. I would like to validate the data in the bank-end to, but I don't want to use annotations.

Here is an example of the code:

    @RequestMapping(value = SecureApiResources.URI_UPDATE_ACCOUNT, method = RequestMethod.POST, produces = "application/json")
    public @ResponseBody Account updateAccount(
            @RequestBody final AccountRequestUpdate accountRequest) { // Object to be validated (accountRequest)

        Account account = accountMapper.getAccountOfMerchant(authContextHolder.getMerchantId(), authContextHolder.getDefaultAccountId());

        if (account == null) {
            HttpErrors httpErrors = new HttpErrors(
                    SecureApiResources.ERROR_ACCOUNTS_NOT_FOUND);
            throw new EntityNotFoundException(httpErrors);
        }
        int resultUpdate;
        try {
            // In this point I should validate the accountRequest object
            account.setAccountName(accountRequest.getAccountName());
            account.setCommercialName(accountRequest.getCommerciaName());
            account.setCountry(accountRequest.getCountry());
            account.setCity(accountRequest.getCity());
            resultUpdate = accountMapper.updateMerchant(account);
            if (resultUpdate == 0) {
                HttpErrors httpErrors = new HttpErrors(
                        SecureApiResources.ERROR_ACCOUNTS_NOT_FOUND);
                throw new EntityNotFoundException(httpErrors);
            }
        } catch (Exception e) {
            HttpErrors httpErrors = new HttpErrors(
                    SecureApiResources.ERROR_SQL_NOT_EXECUTE);
            throw new EntityNotFoundException(httpErrors);
        }

        return account;
    }

In the same class I have a method to create an account and I reciebe another model object (AccountRequestCreate accountRequest).

Which could be the most recommended option to implement without xml neither annotations?

Ironically, the most recommend approach is using @Valid or @validated annotations! What's the problem of annotations? You've already added a @RequestBody, i guess you can make room for one more annotation. — Ali Dehghani
– Ali Dehghani, Commented Mar 4, 2016 at 19:38

Ali Dehghani · Accepted Answer · 2016-03-11 11:29:48Z

The most recommended approach is using @Valid or @Validated annotations but since you're not totally OK with that, you can Autowire the javax.validation.Validator into your controller and perform the validation manually:

@Controller
public class SomeController {
    @Autowired private Validator validator;

    @RequestMapping(...)
    public ResponseEntity<?> someHandler(@RequestBody SomeBody body) {
        Set<ConstraintViolation<SomeBody>> violations = validator.validate(body);
        if (!violations.isEmpty()) {
            List<String> messages = violations
                                   .stream()
                                   .map(ConstraintViolation::getMessage)
                                   .collect(Collectors.toList());

            return ResponseEntity.badRequest().body(messages);
        }
        // the rest of controller
    }
}

With this approach, you will repeat the validation logic in all other controllers which is, well, not a good idea. Also you're violating the DRY principle.

As i said it's better to annotate your bean with @Valid or @Validated:

@RequestMapping(...)
public ResponseEntity<?> someHandler(@RequestBody @Valid SomeBody body) { ... }

If passed bean violates at least one validation rule, an MethodArgumentNotValidException would be thrown. For handling that exception you can write a ControllerAdvice that catches the exception and return a suitable HTTP response, say a 400 Bad Request:

@ControllerAdvice
public class ValidationAdvice {
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<?> handleValidationError(MethodArgumentNotValidException ex) {
         List<String> validationErrors = ex.getBindingResult()
                                            .getAllErrors()
                                            .stream()
                                            .map(ObjectError::getDefaultMessage)
                                            .collect(Collectors.toList());

         return ResponseEntity.badRequest().body(validatioErrors);
    }
}

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