将服务自动装配到验证器中

Question

这个例子有点人为; 我简化了它以删除无关的细节,并专注于我遇到的问题.我有一个看起来像这样的验证器:

@Component
public class UniqueUsernameValidator implements ConstraintValidator<UniqueUsername, String> {

    @Autowired
    UsernameService usernameService;

    @Override
    public void initialize(UniqueUsername uniqueUsername) {
    }

    @Override
    public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
        return !usernameService.exists(s);
    }   
}

我从我的控制器调用验证器,如下所示:

@RequestMapping
public void checkUsername(Model model, User user) {
    ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
    Validator validator = factory.getValidator();

    Set<ConstraintViolation<User>> constraintViolations = validator.validateProperty(user, "username");
    model.addAttribute("error", constraintViolations.size() > 0);
}

但是,我一直有NullPointerException例外.我在验证器添加一个断点,并看到usernameService了null.为什么不进行自动装配？最初我认为这是因为我没有注释验证器@Component,但即使在注释它之后我仍然有同样的问题.该UsernameService班已经标注了@Service,我可以验证它的构造函数获取调用.

我是Spring的新手,所以我甚至不确定将服务连接到验证器是否可以.我究竟做错了什么？

Answer 1

在Spring中,您需要获取ValidatorFactory(或Validator自身)via LocalValidatorFactoryBean而不是Validation.buildDefaultValidatorFactory(),如引用中所述.

@Autowired
Validator validator;

@RequestMapping 
public void checkUsername(Model model, User user) { 
    Set<ConstraintViolation<User>> constraintViolations = validator.validateProperty(user, "username"); 
    model.addAttribute("error", constraintViolations.size() > 0); 
} 

-

<bean id="validator"
    class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"/>

编辑:但也许更好的方法是使用Spring MVC的自动验证和@Valid注释:

@RequestMapping  
public void checkUsername(Model model, @Valid User user, BindingResult result) {  
    if (result.hasErrors()) {   
        ...
    }
}

这<mvc:annotation-driven/>在配置中也需要.