[cdi-dev] Subclassing?

[Stuart Douglas]

Mark Struberg wrote:
> Not sure if the trick with the ThreadLocal would work (aside from being dog slow).
> A->B->A should all lead to decorator invocations. Is this the case with your impl? (B might be another Decorator or a simple Bean)

Depends if B is a normal scoped bean or not. I agree this is not ideal.

To be honest I think it may actually be better to tighten the 
requirements for intercepted/decorated beans to allow interception to be 
implemented via a proxy. The way the CDI 1.0 spec was written this was 
not really possible to do and still be spec compliant (although the TCK 
did not test this), but we could change to 1.1 spec to require all 
intercepted classes to meet the proxiability requirements.

Basically as I see it the pros/cons of each are:

Subclassing:

Pros:
1. Can use reflection to read fields / bean can have public fields
2. No proxiability requirement
3. Constructor is only called once

Cons:
4. Self invocation cannot be handled consistently
5. Implementation is more complex
6. For normal scoped beans the bean has to be proxied anyway, so there 
is no advantage


Proxying:

Pros:
7. Consistent with all other interceptor behavior
8. Self invocation works as expected

Cons:
9. Bean must meet proxiability requirements (although you can get around 
this with JVM specific hacks)
10. Constructor will be called twice

I do not consider 1. to be worth considering as a real advantage (public 
fields == yuck). Basically the only advantage that sub classing has is 
when you are dealing with a dependent scoped bean that would not meet 
the proxyability requirements. I think in this case adding a default 
constructor to enable the bean to be proxied is not a big deal.

Stuart


>
> LieGrue,
> strub
>
>
>
>
> ----- Original Message -----
>> From: Stuart Douglas<stuart.w.douglas at gmail.com>
>> To: Mark Struberg<struberg at yahoo.de>
>> Cc: Pete Muir<pmuir at redhat.com>; Romain Manni-Bucau<rmannibucau at gmail.com>; "cdi-dev at lists.jboss.org"<cdi-dev at lists.jboss.org>
>> Sent: Monday, September 17, 2012 11:31 PM
>> Subject: Re: [cdi-dev] Subclassing?
>>
>>
>>
>> Mark Struberg wrote:
>>>   The main difference we get from subclassing is that even 'internal
>> invocations' (contrary to 'external invocations') will invoke the
>> decorator method
>>>   example
>>>
>>>   public Class A implements X {
>>>
>>>
>>>      public void methA() {..}
>>>      public void methB() { methA(); }
>>>
>>>   }
>>>
>>>   @Decorator
>>>   public class Adecorator implements X {
>>>      @Inject @Delegate X x;
>>>
>>>      public void methA();
>>>   }
>>>
>>>   If we do _not_ apply subclassing but proxying, then invoking methB will NOT
>> trigger methA from Adecorator.
>>>   If we DO force subclassing, then a call to methB will also trigger the
>> decorator!
>>>   But that is contrary to all other EE proxying behaviour so far...
>>
>> In weld we currently use a thread local to work around this, so self
>> invocation does not result in interceptors / decorators running again.
>>
>> Stuart
>>
>>>
>>>   LieGrue,
>>>   strub
>>>
>>>
>>>
>>>   ----- Original Message -----
>>>>   From: Pete Muir<pmuir at redhat.com>
>>>>   To: Romain Manni-Bucau<rmannibucau at gmail.com>
>>>>   Cc: "cdi-dev at lists.jboss.org"<cdi-dev at lists.jboss.org>
>>>>   Sent: Monday, September 17, 2012 5:58 PM
>>>>   Subject: Re: [cdi-dev] Subclassing?
>>>>
>>>>   Romain,
>>>>
>>>>   I agree, we can't specify to use subclassing. Please take a look at
>>>>   https://github.com/jboss/cdi/pull/117 where I've tried to address
>> this, in
>>>>   terms of what effects people will see.
>>>>
>>>>   On 17 Sep 2012, at 16:54, Romain Manni-Bucau wrote:
>>>>
>>>>>     Hi,
>>>>>
>>>>>     There is a bunch of jira to specify subclassing should be used in
>> some
>>>>   cases so i mail here instead of answering all jira.
>>>>>     IMO it is specifying too much the technical part:  specify the
>> constructor
>>>>   should be called twice is better for a spec IMHO (but this case is not
>> logical
>>>>   at all ;))
>>>>>     Why this need?
>>>>>
>>>>>     - Romain
>>>>>
>>>>>     _______________________________________________
>>>>>     cdi-dev mailing list
>>>>>    cdi-dev at lists.jboss.org
>>>>>    https://lists.jboss.org/mailman/listinfo/cdi-dev
>>>>   _______________________________________________
>>>>   cdi-dev mailing list
>>>>   cdi-dev at lists.jboss.org
>>>>   https://lists.jboss.org/mailman/listinfo/cdi-dev
>>>>
>>>   _______________________________________________
>>>   cdi-dev mailing list
>>>   cdi-dev at lists.jboss.org
>>>   https://lists.jboss.org/mailman/listinfo/cdi-dev