[cdi-dev] Can an observer be both async and sync?

[Martin Kouba]

Well, it's not 100% clear but I believe it should be forbidden. The spec 
only states:

"An observer method may be declared by annotating a parameter 
@javax.enterprise.event.Observes OR 
@javax.enterprise.event.ObservesAsync of a default-access, public, 
protected or private method. That parameter is the event parameter."

I think it wouldn't hurt to add:

"If an event parameter is annotated with both @Observes and 
@ObservesAsync, the container automatically detects the problem and 
treats it as a definition error."

Weld throws a DefinitionException.

Martin

Dne 6.3.2017 v 07:55 Tomas Remes napsal(a):
>
> Hi John,
>
> No it shouldn't. The problematic and confusing case would be when there is some other param (injection point) in this observer method and this param resolves to let's say @SessionScoped bean. How does it work then? Once it fails (since there's no context propagation for async event), once it works (sync event)? Therefore this was forbidden.
>
> Tom
>
> ----- Original Message -----
> From: "John Ament" <john.ament at spartasystems.com>
> To: "cdi-dev" <cdi-dev at lists.jboss.org>
> Sent: Monday, March 6, 2017 1:42:09 AM
> Subject: [cdi-dev] Can an observer be both async and sync?
>
>
>
> Section 10.4.4 has the following section which got me thinking
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> public void refreshOnDocumentUpdate(@Observes(notifyObserver=IF_EXISTS) @Updated Document doc) { ... }
>
> public void asyncRefreshOnDocumentUpdate(@ObservesAsync(notifyObserver=IF_EXISTS) @Updated Document doc) { ... }
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> I'm wondering, is it OK to have an observer method defined like this?
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> public void asyncRefreshOnDocumentUpdate( @Observes(notifyObserver=IF_EXISTS) @ObservesAsync(notifyObserver=IF_EXISTS) @Updated Document doc) { ... }
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> I don't see anything against this in the spec, but I suspect most people are going to think this shouldn't work. So I'm asking the question - should it work?
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> John
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-- 
Martin Kouba
Senior Software Engineer
Red Hat, Czech Republic