[cdi-dev] Should javax.enterprise.inject.Produces be inherited?

Emily Jiang EMIJIANG at uk.ibm.com
Tue Sep 13 09:34:07 EDT 2016


John,

Basically what you suggested is to omit the @Produces on overriding the 
producer methods. 

I am trying to spell out the gap: I am not sure whether the user scenario, 
where you would override the method but not adding @Produces, is useful. 
Is this potentially used by any testing apps? If you don't add @Produces 
on overriding a producer method, when the container calls the producer 
method, which one will be invoked?

Something related to this area, for the following two code snippets, the 
first producer is a kind of alternative even though not annotating with 
@Alternative. They are the same, right?

@Alternative
@Priority(100)
@ApplicationScoped
public class BoopAlternative extends Boop{
    @Override
    @Produces
    public Simpler makeSimpler() {
        return new Simpler("Boop2");
    }

@Alternative
@Priority(100)
@ApplicationScoped
public class BoopAlternative extends Boop{
    @Override
    @Produces
    @Alternative
    public Simpler makeSimpler() {
        return new Simpler("Boop2");
    }


Many thanks,
Emily
===========================
Emily Jiang
WebSphere Application Server, CDI Development Lead
 
MP 211, DE3A20, Winchester, Hampshire, England, SO21 2JN
Phone:  +44 (0)1962 816278  Internal: 246278

Email: emijiang at uk.ibm.com 
Lotus Notes: Emily Jiang/UK/IBM at IBMGB




From:   John Ament <john.ament at spartasystems.com>
To:     Emily Jiang/UK/IBM at IBMGB
Cc:     cdi-dev <cdi-dev at lists.jboss.org>
Date:   13/09/2016 11:38
Subject:        Re: [cdi-dev] Should javax.enterprise.inject.Produces be 
inherited?
Sent by:        cdi-dev-bounces at lists.jboss.org



Emily,

Just want to make sure I follow.  Are you saying this because right now it 
is required that you add @Produces to the overridden method?

I don't realistically see a scenario where you would override the method 
and not add produces.  This method is intended to be called by the 
container.

John



From: Emily Jiang <EMIJIANG at uk.ibm.com>
Sent: Tuesday, September 13, 2016 4:37 AM
To: John Ament
Cc: Matej Novotny; Mark Struberg; cdi-dev
Subject: Re: [cdi-dev] Should javax.enterprise.inject.Produces be 
inherited? 
 
First of all, the subject line suggests the produces should be inherited 
under all conditions. Anyway, after your explanation, I think this 
suggestion contradicts with spec and breaks backward compatibility. In the 
cdi 1.2/cdi 2.0 spec, 


The only way one bean can completely override a second bean at all 
injection points is if it implements all the bean types and declares all 
the qualifiers of the second bean. However, if the second bean declares a 
producer method or observer method, then even this is not enough to ensure 
that the second bean is never called! 
To help prevent developer error, the first bean may: 
directly extend the bean class of the second bean, or 
directly override the producer method, in the case that the second bean is 
a producer method, and then
explicitly declare that it specializes the second bean. 
After this suggestion, the above sentence is not true any more. 

Many thanks,
Emily
===========================
Emily Jiang
WebSphere Application Server, CDI Development Lead 
 
MP 211, DE3A20, Winchester, Hampshire, England, SO21 2JN
Phone:  +44 (0)1962 816278  Internal: 246278

Email: emijiang at uk.ibm.com 
Lotus Notes: Emily Jiang/UK/IBM at IBMGB




From:        John Ament <john.ament at spartasystems.com> 
To:        Matej Novotny <manovotn at redhat.com>, Mark Struberg 
<struberg at yahoo.de> 
Cc:        Emily Jiang/UK/IBM at IBMGB, cdi-dev <cdi-dev at lists.jboss.org> 
Date:        12/09/2016 13:31 
Subject:        Re: [cdi-dev] Should javax.enterprise.inject.Produces be 
inherited? 
Sent by:        cdi-dev-bounces at lists.jboss.org 



@Matej - Yes, that would be consistent with what I was seeing as well. 

@Mark - Are you thinking about decorators and not alternatives?  See also 
[1] 
Really the goal here is to substitute the bean, but not just the provided 
bean the producer method that it exposes.  It seems to work as I would 
expect it in weld (as mentioned), when I add @Produces to the method, it 
overrides the base class's producer method.  No ambiguous resolutions, it 
just works properly. 

Realistically, this is all an experiment to see if I can provide spring 
boot like default configurations (beans, config values, etc) in a 
framework, and override them as an application developer. 


[1]: http://docs.jboss.org/cdi/spec/2.0.EDR2/cdi-spec.html#alternatives 



From: Matej Novotny <manovotn at redhat.com>
Sent: Monday, September 12, 2016 3:28 AM
To: Mark Struberg
Cc: John Ament; Emily Jiang; cdi-dev
Subject: Re: [cdi-dev] Should javax.enterprise.inject.Produces be 
inherited? 
  
Hi all,

I did some testing (with Weld) and it seems the scope IS inherited when 
you use @Alternative.
However it IS NOT inherited when you use @Specialized.

Not yet sure if this is intended or anyhow spec-defined, just stating 
facts.

Matej

----- Original Message -----
> From: "Mark Struberg" <struberg at yahoo.de>
> To: "John Ament" <john.ament at spartasystems.com>, "Emily Jiang" 
<EMIJIANG at uk.ibm.com>
> Cc: "cdi-dev" <cdi-dev at lists.jboss.org>
> Sent: Monday, September 12, 2016 8:00:55 AM
> Subject: Re: [cdi-dev] Should javax.enterprise.inject.Produces be 
inherited?
> 
> 
> 
> > Right now inheritance of managed beans is itself problematic, as
> 
> > injecting the base class can cause these ambiguous resolutions.
> 
> Yes, that's why we originally introduced @Typed.
> 
> 
> 
> Your sample wont work as an Alternative as it extends a concrete class 
and
> doesn't implement any interface.
> Did you mean @Specializes?
> Note that with @Alternative you won't make the original producer go 
away.You
> would also need to add @Alternative to the producer method imo. The 
rules
> for making an alternative producer method are really a bit confusing ;) 
I
> think the most portable way is to annotate both the class and the 
producer
> method with @Alternative.
> 
> 
> LieGrue,
> strub
> 
> 
> On Monday, 12 September 2016, 0:57, John Ament 
<john.ament at spartasystems.com>
> wrote:
> >
> >Hi Emily,
> >
> >
> >I disagree, at least it doesn't add any new ambiguous injections.  The
> >use-case is specifically to Specialized/Alternative beans.  Right now
> >inheritance of managed beans is itself problematic, as injecting the 
base
> >class can cause these ambiguous resolutions.
> >
> >
> >The example I sent out actually works correctly (in weld at least), 
really
> >my propose is to remove the need to have Produces a second time and 
update
> >the spec to clarify what happens here (FWIW, I don't believe the case 
is
> >currently described in the spec), hopefully to say that qualifiers and
> >scopes from the base method remain in effect, unless explicitly 
overridden.
> >
> >
> >John
> >
> >
> >
> >________________________________
> > 
> >From: Emily Jiang <EMIJIANG at uk.ibm.com>
> >Sent: Sunday, September 11, 2016 5:59 PM
> >To: John Ament
> >Cc: cdi-dev
> >Subject: Re: [cdi-dev] Should javax.enterprise.inject.Produces be 
inherited?
> > 
> >I think this is very problematic as you will get
> >AmbiguousResolutionException all the time once we introduce this
> >inheritance.
> >
> >Many thanks,
> >Emily
> >===========================
> >Emily Jiang
> >WebSphere Application Server, CDI Development Lead
> > 
> >MP 211, DE3A20, Winchester, Hampshire, England, SO21 2JN
> >Phone:  +44 (0)1962 816278  Internal: 246278
> >
> >Email: emijiang at uk.ibm.com
> >Lotus Notes: Emily Jiang/UK/IBM at IBMGB
> >
> >
> >
> >
> >From:        John Ament <john.ament at spartasystems.com>
> >To:        cdi-dev <cdi-dev at lists.jboss.org>
> >Date:        11/09/2016 20:04
> >Subject:        [cdi-dev] Should javax.enterprise.inject.Produces be
> >inherited?
> >Sent by:        cdi-dev-bounces at lists.jboss.org
> >>________________________________
> > 
> >
> >
> >All,
> >
> >I was just thinking about alternatives and producer methods.  Suppose I 
have
> >the following bean:
> >
> >@ApplicationScoped
> >public class Boop {
> >
> >    @Produces
> >    @ApplicationScoped
> >    public Simpler makeSimpler() {
> >        return new Simpler("Boop");
> >    }
> >}
> >
> >If I want to override the producer method, I need to declare fully:
> >
> >@Alternative
> >@Priority(100)
> >@ApplicationScoped
> >public class BoopAlternative extends Boop{
> >    @Override
> >    @Produces
> >    public Simpler makeSimpler() {
> >        return new Simpler("Boop2");
> >    }
> >}
> >
> >For some reason, scopes are inherited, but the produces annotation is 
not.
> >At least in the case of a producer method, it seems like it would be
> >useful for @Produces to be inherited as well.
> >
> >John
> >
> >________________________________
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