@Configuration
@ComponentScan("com.test.project")
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

...

    @Bean
    public MessageSource messageSource() {
        ReloadableResourceBundleMessageSource messageSource = new ReloadableResourceBundleMessageSource();
        messageSource.setBasenames("resources");
        messageSource.setUseCodeAsDefaultMessage(true);
        messageSource.setDefaultEncoding("UTF-8");
        messageSource.setFallbackToSystemLocale(false);
        return messageSource;
    }
}

user.loginIsEmpty = Login is required.
user.login = Login must be between 8 and 16 characters.
user.duplicateLogin = Such login already exists.
user.passwordIsEmpty = Password is required.
user.password = Password must be over 8 characters.
user.confirmPasswordIsEmpty = Confirm password is required.
user.differentPassword = Password don't match.

@Component
public class UserValidator implements Validator {

    @Autowired
    private UserService userService;

    @Override
    public boolean supports(Class<?> aClass) {
        return User.class.equals(aClass);
    }

    @Override
    public void validate(Object o, Errors errors) {
        User user = (User) o;

        ValidationUtils.rejectIfEmptyOrWhitespace(errors, "login", "user.loginIsEmpty");
        String login = user.getLogin();
        String password = user.getPassword();
        if (login.length() > 16 || login.length() < 8)
            errors.rejectValue("login", "user.login");

        ValidationUtils.rejectIfEmptyOrWhitespace(errors, "password", "user.passwordIsEmpty");
        ValidationUtils.rejectIfEmptyOrWhitespace(errors, "confirmPassword", "user.confirmPasswordIsEmpty");

        if (password.length() < 8)
            errors.rejectValue("password", "user.password");

        if (!password.equals(user.getConfirmPassword()))
            errors.rejectValue("confirmPassword", "user.differentPassword");

        if (userService.getByLogin(login) != null)
            errors.rejectValue("login", "user.duplicateLogin");
    }
}

@Controller
public class RegController {

    @Autowired
    UserValidator userValidator ;

    @Autowired
    private SecurityService securityService;

    @Autowired
    private UserService userService;


    @RequestMapping(value = "/reg", method = RequestMethod.GET)
    public String signUp(Model model) {
        model.addAttribute("user", new User());
        return "reg";
    }

    @RequestMapping(value = "/reg", method = RequestMethod.POST)
    public String signUp(@ModelAttribute("user") User user, BindingResult bindingResult, Model model) {
        userValidator.validate(user, bindingResult);
        if (!bindingResult.hasErrors()) {
            userService.create(passenger);
            return "/index";
        }
        else
            return "/reg";
    }
}

<form:form method="POST" modelAttribute="passenger">
    <spring:bind path="login">
        <div class="form-group ${status.error ? 'has-error' : ''}">
            <form:input type="text" path="login" class="form-control" placeholder="Login"></form:input>
            <form:errors path="login"></form:errors>
        </div>
    </spring:bind>

    <spring:bind path="password">
        <div class="form-group ${status.error ? 'has-error' : ''}">
            <form:input type="password" path="password" class="form-control" placeholder="Password"></form:input>
            <form:errors path="password"></form:errors>
        </div>
    </spring:bind>

    <spring:bind path="confirmPassword">
        <div class="form-group ${status.error ? 'has-error' : ''}">
            <form:input type="password" path="confirmPassword" class="form-control" placeholder="Confirm your password"></form:input>
            <form:errors path="confirmPassword"></form:errors>
        </div>
    </spring:bind>

    <button type="submit">Submit</button>
</form:form>

@Configuration
@PropertySource(value = {"file:resources/message.properties"})

@Configuration
@PropertySource(value = {"file:/opt/common_resources/message.properties"})

@Bean
public void properties(
        @Value("${user.loginIsEmpty}") String loginIsEmpty,
        @Value("${user.login}") String login,
        @Value("${user.duplicateLogin}") String duplicateLogin,
        @Value("${user.passwordIsEmpty}") String password,
        @Value("${user.confirmPasswordIsEmpty}") String confirmPasswordIsEmpty,
        @Value("${user.differentPassword}") String differentPassword,
) {
    // Работа с данными
}