[cdi-dev] [JBoss JIRA] Commented: (CDI-4) Need a way to provide ordering for Event observers (@Observes)

Mark Struberg (JIRA) jira-events at lists.jboss.org
Sun May 8 05:20:18 EDT 2011

    [ https://issues.jboss.org/browse/CDI-4?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12600520#comment-12600520 ] 

Mark Struberg commented on CDI-4:

John, think you mean the discussion over in CDI-7, right?

Btw, good discussion right now. Think we are moving forward.

I understand that magic numbers is not an optimal idea neither. So lets step back a bit and look at the problem from the distance. 

* the @Before doesn't scale out in practice. You cannot always change your event if someone adds a jar into the classpath which needs that event
* the @After is not necessary. The problems you explained can also easily get solved with the current spec. See my example below

The original code just throws the original Event:
BeanManager.fire(new MyEvent());

The 'before' observes this event, does some security checks and rethrows it with a qualifier @Secured

public void checkSecurity(@Observes MyEvent me) {
  bm.fire(me, SecuredAnnotationLiteral);

The 'after' then just observes the @Secured version of the event
public void doThaRealThing(@Observes @Secured MyEvent me) {

I'm coming always closer to the firm conviction that we should pull out the observer ordering into an external config, as we did with interceptor ordering.

> Need a way to provide ordering for Event observers (@Observes)
> --------------------------------------------------------------
>                 Key: CDI-4
>                 URL: https://issues.jboss.org/browse/CDI-4
>             Project: CDI Specification Issues
>          Issue Type: Feature Request
>          Components: Events, Portable Extensions
>    Affects Versions: 1.0
>         Environment: All
>            Reporter: Lincoln Baxter III
>            Assignee: Mike Brock
>             Fix For: TBD
> There needs to be a way to specify some kind of ordering for Event observers. 
> Understandably, this is somewhat counter-intuitive to the general concept of observing an event, but there is going to be need for this in an upcoming JBoss project. While it can be done manually, it might be nice to have a built-in API.

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