[cdi-dev] [JBoss JIRA] (CDI-43) Allow Extensions to specify the annotations that they are interested in

[Jozef Hartinger (JIRA)]

    [ https://issues.jboss.org/browse/CDI-43?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12727995#comment-12727995 ] 

Jozef Hartinger commented on CDI-43:
------------------------------------

Several consequences are implicit and we should discuss whether these are expected and/or should be declared explicitly:

h3. Overriding

As per current proposal of https://issues.jboss.org/browse/CDI-132, AnnotatedType.getMethods() returns even those methods that are overridden. Therefore in this situation:

{code:JAVA}
public class SimpleExtension implements Extension {

   void observe(@Observes @WithAnnotations(Blah.class) ProcessAnnotatedType<Bar> event)
}

public class Foo {

   @Blah
   public void ping() {
   }
}

public class Bar extends Foo {

   // no annotation here
   public void ping() {
   }

}
{code}

The observer method would be invoked for ProcessAnnotatedType<Bar> even though Bar does not effectively use the @Blah annotation.

h3. Modification by extensions

Having a class

{code:JAVA}
@Bar
public class Foo {
}
{code}

there may be multiple observers of ProcessAnnotatedType<Foo>. These observers may modify the annotated type and therefore modify the annotations that the type provides. That means that if there are extension observer methods:

{code:JAVA}
void observe1(@Observes ProcessAnnotatedType<Foo> event) {
   event.setAnnotatedType(removeBar(event.getAnnotatedType)); // removes @Bar from the annotated type
}

void observe2(@Observes @WithAnnotations(Bar.class) ProcessAnnotatedType<Foo> event) {
}
{code}

We can either:

* resolve the observer methods upfront and invoke observe2 even if observe1 has been invoked before and the AnnotatedType no longer contains Bar which is required by observe2.
* check the annotations of an AnnotatedType after each modification of the AnnotatedType and only invoke the other observer method if the AnnotatedType still matches its requirements

The latter approach seems wrong. Since the order of observer method invocation is not specified, this could lead to random results. (the result would be dependent on the unspecified order)

However, from the extension developer perspective it may be confusing if the observe2 method is invoked but the AnnotatedType contains no @Bar even though the observer methods defined @WithAnnotations(Bar.class), so we should probably document that this may happen.
                
> Allow Extensions to specify the annotations that they are interested in
> -----------------------------------------------------------------------
>
>                 Key: CDI-43
>                 URL: https://issues.jboss.org/browse/CDI-43
>             Project: CDI Specification Issues
>          Issue Type: Feature Request
>          Components: Portable Extensions
>    Affects Versions: 1.0
>            Reporter: Stuart Douglas
>            Assignee: Pete Muir
>             Fix For: 1.1 (Proposed)
>
>
> Currently portable extensions that wish to look for a specific annotation have to look through all availible classes in the ProcessAnnotatatedType event, which is quite inefficient. It would be good if extensions could do something like:
> public void processAnnotatedType(@Observes @RequireAnnotations({@Unwraps.class}) ProcessAnnotatedType pat) 
> This could allow the container to take advantage of annotation indexing to improve boot time performance, as well as reducing uneeded processing in the observer.

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