[bv-dev] Do we need ConstraintValidatorFactory#releaseInstance()?

[Hardy Ferentschik]

Hi,

I agree with Gunnar. Assuming that most (or at least the most popular) decency injection frameworks have support for @PreDestroy (or equivalent),
it would be simpler to just state in the spec that it is the responsibly of the dependency injection enabled ConstraintValidatorFactory to release validators 
when the factory itself gets destroyed. 

Does anyone have a good use case for an explicit ConstraintValidatorFactory#releaseInstance or an example of a framework which would not be able
to integrate with Bean Validation when releaseInstance would be removed. If not, I second Gunnar's suggestions of removing the method and changing the spec.

--Hardy



On 3 Jan 2012, at 12:44 PM, Gunnar Morling <gunnar at hibernate.org> wrote:

> Hi all,
> 
> The latest RI version [1] also implements the spec changes regarding the integration of BV and CDI.
> 
> During implementation Hardy, Emmanuel and I got into a discussion regarding the lifecycle of CDI-managed objects [2] which I'd like to continue. 
> 
> The question is whose responsibility is it to release involved objects such as message interpolator, traversable resolver or constraint validators. Generally we think objects should be released by that party/code that created them.
> 
> This means:
> 
> 1) objects created by the user and passed via bootstrap API: to be released by user
> 2) objects created by BV implementation (e.g. internal caches): to be released by BV implementation
> 3) objects passed by CDI integration layer (e.g. CDI-enabled message interpolator etc. based on BootstrapConfiguration): to be released by integration layer
> 
> I think 1) is not in our focus, let the user deal with it. For 2) we have ValidatorFactory#close(). Interesting is 3). A CDI portable extension could make sure that its created managed beans are properly released using CDI's pre-destroy hook [3].
> 
> But that way a CDI-enabled ConstraintValidatorFactory could also easily release all the constraint validators it created:
> 
> CdiConstraintValidatorFactory implements ConstraintValidatorFactory {
> 
>   public <T extends ConstraintValidator<?, ?>> T getInstance(Class<T> key) {
>     //create validators. keep track of them. 
>   }
> 
>   @PreDestroy
>   public cleanUpValidators() {
>     //release created validators
>   }
> }
> 
> That is, we'd again adhere to the principle that whoever creates objects has to release them. When following this approach, we actually wouldn't need ConstraintValidatorFactory#releaseInstance() anymore. I think this would be a good thing as it IMO simplifies the contract between the BV provider and code integrating with it (such as a CDI portable extension) and clarifies responsibilities.
> 
> In the spec we would describe that a CDI-enabled CVF has to release its validators when it itself is going to be destructed and for ValidatorFactory#close(), that a BV provider has to release its internal state but no objects passed to it.
> 
> One thing not possible with that approach is to release CV instances before the application is shut down. The spec currently says that releaseInstance() is "typically" invoked when the ValidatorFactory is closed, but AFAICS it leaves room for releasing constraint validators also in between. OTOH I wouldn't know when/how a BV provider would decide to do that.
> 
> Any thoughts?
> 
> --Gunnar
> 
> [1] http://in.relation.to/Bloggers/HibernateValidator500Alpha2And431Final
> [2] https://hibernate.onjira.com/browse/BVAL-338
> [3] http://docs.oracle.com/javaee/6/tutorial/doc/gmgkd.html
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