JSR 303 Country code validator with java locale

CountryCodeValidator.java

public class CountryCodeValidator implements ConstraintValidator<ValidIso2CountryCode, String> {

    private static final Set<String> isoCountries = Locale.getISOCountries(Locale.IsoCountryCode.PART1_ALPHA2);

    @Override
    public boolean isValid(String content, ConstraintValidatorContext context) {
        if (content == null) {
            setErrorMessage(context, "Country code must not be null");
            return false;
        }
        boolean contains = isoCountries.contains(content.toUpperCase());
        if (!contains) {
            setErrorMessage(context, "Invalid country code "+content);
        }
        return contains;
    }

    private void setErrorMessage(ConstraintValidatorContext context, String message) {
        context.disableDefaultConstraintViolation();
        context.buildConstraintViolationWithTemplate(message).addConstraintViolation();
    }
}

ValidIso2CountryCode.java

@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = { CountryCodeValidator.class })
public @interface ValidIso2CountryCode {

    String message() default "iso2 country code invalid";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}