Injecting Spring Dependencies into ConstrantValidator

Question

I\'m using Bean Validation. I have a custom validator @MyValidator that needs to look up a value with an injected Spring managed DAO object. How can I get access t

Answer 1

The minimum setup for @Autowired to work properly in ConstraintValidator implementation is to have this bean in a Spring @Configuration:

    @Bean
    public Validator defaultValidator() {
        return new LocalValidatorFactoryBean();
    }

This allows any beans, including ApplicationContext, to be injected directly into a ConstraintValidator:

@Constraint(validatedBy = DemoValidator.class)
public @interface DemoAnnotation {
    // ...
    Class<?> beanClass();
}

public class DemoValidator implements ConstraintValidator<DemoAnnotation, String> {

    private final ApplicationContext applicationContext;

    private Object bean;

    @Autowired
    public DemoValidator(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @Override
    public void initialize(DemoAnnotation constraint) {
        Class<?> beanClass = constraint.beanClass();
        bean = applicationContext.getBean(beanClass);
    }

    @Override
    public boolean isValid(String obj, ConstraintValidatorContext context) {
        return !obj.isEmpty();
    }
}

Demo

For a really flexible validation solution I would recommend Jakub Jirutka's Bean Validator utilizing Spring Expression Language (SpEL) which allows things like:

public class Sample {

    @SpELAssert("@myService.calculate(#this) > 42")
    private int value;
}