Database access from jsr-303 custom validator

问题

I'm using spring based validation in combination with hibernate validator enabled by the following in my application context:

<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        ....
        <property name="jpaPropertyMap">
            <map>
                <entry key="javax.persistence.validation.factory" value-ref="validator" />    
            </map>
        </property>
    </bean>

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

I've implemented a custom validator that accesses a database to check validity constraints for a particular object using a spring injected DAO. This results in a java.lang.StackOverflowError as it appears that the validation is called every time an object is loaded from the database from within the validator, causing an infinite loop. To get around this, I have tried setting the flush mode on my entity manager to commit from within the validator with the following code:

entityManager.setFlushMode(FlushModeType.COMMIT);

This results in an "collection not process by flush()" exception from hibernate.

Is there an example of best practice in accessing the database from within a custom validator which will allow me to get around both of these issues?

回答1:

After much experimentation, it would appear that the best way to do this to is to use the EntityManagerFactory directly from within the code. In the initialize(...) method of the validator class I have the following code:

EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu_name");
entityManager = emf.createEntityManager();

The downside is that you don't get Spring's DI features, but you can access the database nonetheless.

回答2:

I ran into this issue as well, here is how I solved it: @Autowired bean works with @Valid on controller but fails with CRUD repository

In a few words, I also got a reference to the EntityManagerFactory object. However, I set setFlushMode to FlushModeType.COMMIT just before calling my service method. Finally I set it back to FlushModeType.AUTO:

Here is an example:

public class UniqueUsernameValidator implements ConstraintValidator<UniqueUsername, String> {

    @PersistenceContext
    private EntityManager em;

    @Autowired
    UserService userService;

    @Override
    public void initialize(UniqueUsername constraintAnnotation) {       
    }

    @Override
    public boolean isValid(String username, ConstraintValidatorContext context) {
        try { 
            em.setFlushMode(FlushModeType.COMMIT);          
            return userService.findByUsername(username) == null;

            } finally { 
           em.setFlushMode(FlushModeType.AUTO);
           }    
    }
}

来源：https://stackoverflow.com/questions/6595354/database-access-from-jsr-303-custom-validator

标签

java

Spring

validation

bean-validation