[cdi-dev] [JBoss JIRA] (CDI-414) Support for "self" injection or intercepted self invocation

[Antoine Sabot-Durand (JIRA)]

    [ https://issues.jboss.org/browse/CDI-414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13164732#comment-13164732 ] 

Antoine Sabot-Durand commented on CDI-414:
------------------------------------------

I relaunch discussion on this ticket since we are on the verge to introduce a new annotation related to "proxy" or "business methods" exception with CDI-527.
This annotation could be designed to support broader proxy related feature than just CDI-527 and could provide a solution to extend proxy generation to self invocation.
Suppose the annotation to be like
{code}
@Target({TYPE})
@Retention(RUNTIME)
@Documented
public @interface AllowProxy {
    boolean withFinalMethods() default true; 
    boolean onSelfInvocations() default false;
}
{code}

{{@AllowProxy}} alone could be used for CDI-527, but this annotation could be used for this ticket.
The code provided by [~struberg] above would become

{code}
@ApplicationScoped
@AllowProxy(selfInvocation=true) //ask the container to create proxy on all invocation
public class CountryService {

  private List<Country> cachedCountries;

  public List<Counry> getCountries() { 
    if (cachedCountries == null) {
       loadCountries(); // this call would be a business method call thanks to the annotation
    }
    return cachedCountries;
  }

  // Transactional aspect will be activated for all calls including from method in the same instance
  @Transactional
  protected synchronized loadCountries() {
   if (countries != null) return;
   countries = em…. load all countries form DB
  }
}
{code}

As [~jharting] stated multiple times above, it is technically doable thanks to subclassing proxy.
It's not done today because CDI was initially aligned on EJB regarding interception.

Today Interceptor spec is no more part EJB and refers to "business method" concept (without defining it) for interception.
CDI has its own definition of "business method" in http://docs.jboss.org/cdi/spec/1.2/cdi-spec.html#biz_method, so we could imagine adding definition for business method with this new annotation and stay consistant with interceptor spec.

> Support for "self" injection or intercepted self invocation
> -----------------------------------------------------------
>
>                 Key: CDI-414
>                 URL: https://issues.jboss.org/browse/CDI-414
>             Project: CDI Specification Issues
>          Issue Type: Bug
>          Components: Resolution
>            Reporter: arjan tijms
>             Fix For: 2.0 (discussion)
>
>
> Many features of CDI and EJB work by means of a proxy that intercepts calls and adds 'aspects'. In Java it's however not possible to decorate the {{this}} pointer, so methods called on the same bean instance from within a method in the bean do not get their 'aspects' applied.
> This is a well known limitation, but in EJB it's possible to work around this by injecting a bean into itself. E.g.
> {code}
> @Stateless
> public class Foo {
>     @EJB
>     private Foo self;
>     // ...
> }
> {code}
> Also see http://adam-bien.com/roller/abien/entry/how_to_self_invoke_ejb
> Unfortunately using CDI and {{@Inject}} this doesn't work. Weld for instance fails the deployment and logs:
> {noformat}
> WELD-001443 Pseudo scoped bean has circular dependencies.
> {noformat}
> See also: http://adam-bien.com/roller/abien/entry/inject_vs_ejb
> Although there are workarounds, it would be great if {{@Inject}} in combination with CDI could support self injection as well.
> With that projects migrating from {{@EJB}} to {{@Inject}} can do so more easily and the capability can be convenient for new projects as well (e.g. calling two separate {{@Transactional}} methods from a single method without being required to create a new bean).



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