Autowiring a service into a validator

Question

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:

Answer 1

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"/>

EDIT: 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()) {   
        ...
    }
}

This also requires <mvc:annotation-driven/> in the config.

Answer 2

Instead of creating a new validator, you have to autowire or inject it to controller. The NPE from the service not being injected as your validator is not being created/managed by spring.