将服务自动装配到验证器中 [英] Autowiring a service into a validator

问题描述

这个例子有些人为的.我已对其进行了简化，以删除多余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:

This example is a bit contrived; I've simplified it to remove extraneous details and to focus on the problem I am having. I have a validator that looks like this:

@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);
    }   
}

我从控制器中调用验证器，如下所示:

I call the validator from my controller like this:

@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，我一直收到NullPointerException异常.我在验证器中添加了一个断点，并看到usernameService是null.为什么不自动接线?最初，我认为这是因为我没有使用@Component注释验证器，但是即使在注释了它之后，我仍然遇到相同的问题. UsernameService类已经用@Service进行了注释，我可以验证其构造函数是否已被调用.

However, I keep getting an NullPointerException exception. I added a breakpoint in my validator and saw that usernameService was null. Why isn't it getting autowired? Initially I thought it was because I hadn't annotated the validator with @Component, but I still have the same problem even after annotating it. The UsernameService class has already been annotated with @Service and I can verify that its constructor is getting called.

我是Spring的新手，所以我什至不确定是否可以将服务连接到验证程序.我在做什么错了?

I am new to Spring, so I'm not even sure if it is alright to wire a service into a validator. What am I doing wrong?

推荐答案

在Spring中，您需要通过LocalValidatorFactoryBean而不是Validation.buildDefaultValidatorFactory()来获取ValidatorFactory(或Validator本身)，如 .

In Spring, you need to obtain ValidatorFactory (or Validator itself) via LocalValidatorFactoryBean instead of Validation.buildDefaultValidatorFactory(), as described in the reference.

@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:但是也许更好的方法是使用带有@Valid批注的Spring MVC的自动验证:

But perhaps the better way to do it is to use Spring MVC's automatic validation with @Valid annotation:

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

这还需要配置中的<mvc:annotation-driven/>.

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