validation of the entered field

Question

in my application, I enter the values of the three parameters, fromCurrency, toCurrency, and amount into the address bar and in the controller. I want to check the correctness of the entered data. But I have generated an exception during the test and nothing goes further Those. I need a code that in the controller will check the correctness of the entered data and, depending on the field in which the error was made, will produce a 400th error with the name of the incorrectly filled field

I'm tried this validation, with

if(!Currency.getAvailableCurrencies().contains(Currency.getInstance(fromCurrency)))

but it's generate exception if Currency doesn't contain fromCurrency

@RestController
class ExchangeController {

    private static final Logger logger = Logger.getLogger(ExchangeController.class.getName());

    @SuppressWarnings("SpringJavaAutowiredFieldsWarningInspection")
    @Autowired
    @Qualifier("dataService")
    private CurrencyExchangeService currencyExchangeService;

    @SuppressWarnings("SameReturnValue")
    @RequestMapping(value = "/", method = RequestMethod.GET, produces = "application/json")
    public String start() {
        return "input parameters";
    }

    @RequestMapping(value = "/convert", method = RequestMethod.GET, produces = "application/json")
    public ExchangeRateDTO converting(@RequestParam("fromCurrency") String fromCurrency,
                                      @RequestParam("toCurrency") String toCurrency,
                                      @RequestParam("amount") String amount) throws IOException {
        if (!Currency.getAvailableCurrencies().contains(Currency.getInstance(fromCurrency))) {

        }
        BigDecimal convertedAmount = currencyExchangeService.convert(fromCurrency, toCurrency, new BigDecimal(amount));
        return new ExchangeRateDTO(fromCurrency, toCurrency, new BigDecimal(amount), convertedAmount);
    }
}

Answer 1

You can use Hibernate Validator to validate the @RequestParam of your controller.

Add this dependency to your pom.xml

<dependency>
    <groupId>org.hibernate.validator</groupId>
    <artifactId>hibernate-validator</artifactId>
    <version>6.0.10.Final</version>
</dependency>

Then you have to enable validation for both request parameters and path variables in your controllers by adding the @Validated annotation like this

@RestController
@RequestMapping("/")
@Validated
public class Controller {
    // ...
}

Then you can add Annotations like @NotNull @Min @Max to your RequestParam Like

@RequestMapping(value = "/convert", method = RequestMethod.GET, produces = "application/json")
    public ExchangeRateDTO converting(@RequestParam("fromCurrency") @NotNull @NotBlank @Size(max = 10) String fromCurrency,
                                      @RequestParam("toCurrency") String toCurrency,
                                      @RequestParam("amount") String amount) throws IOException {
        if (!Currency.getAvailableCurrencies().contains(Currency.getInstance(fromCurrency))) {

        }
        BigDecimal convertedAmount = currencyExchangeService.convert(fromCurrency, toCurrency, new BigDecimal(amount));

You can also define custom annotations for your needs.

There is more detailed and nice article here