[cdi-dev] Subclassing?
Mark Struberg
struberg at yahoo.de
Tue Sep 18 10:31:01 EDT 2012
Well, I think that is not exactly the case here.
In OWB I once tried subclassing but reverted it back to a proxy based solution because I couldn't get it right.
Status OWB: proxy for Decorators
In Weld it once was a proxy, then they moved to subclassing with a few hacks because the CDI specified behaviour is a mixture between subclassing and proxy effects. As I already showed (A->B->A) this solution is only 70% working (with nasty side effects for the other 30%). It also cannot work any @NormalScoped beans and for @Dependent beans which are intercepted. And I fear it's pretty hard to get this implemented
Status Weld: proxy in older versions, partially broken subclassing in newer versions
Stu, Pete, is this summary correct?
If so then I see not much reason for not not moving back to proxies for Decorators again.
LieGrue,
strub
>________________________________
> From: Joseph Bergmark <bergmark at us.ibm.com>
>To: Pete Muir <pmuir at redhat.com>
>Cc: "cdi-dev at lists.jboss.org" <cdi-dev at lists.jboss.org>
>Sent: Tuesday, September 18, 2012 3:35 PM
>Subject: Re: [cdi-dev] Subclassing?
>
>
>FWIW I agree with Mark & Stu, but isn't backwards compatibility a concern here for implementations that previously supported subclassing?
>
>Pete Muir ---09/18/2012 05:01:07 AM---I'm happy to go with whatever you guys agree on here :-) Marius, I guess you are the only dissenter
>
>
>
>
>Pete Muir <pmuir at redhat.com>
>
>
>Mark Struberg <struberg at yahoo.de>,
>
>
>"cdi-dev at lists.jboss.org" <cdi-dev at lists.jboss.org>
>
>
>09/18/2012 05:01 AM
>
>
>Re: [cdi-dev] Subclassing?
>
>
>cdi-dev-bounces at lists.jboss.org
>________________________________
>
>
>
>I'm happy to go with whatever you guys agree on here :-)
>
>Marius, I guess you are the only dissenter now :-) WDYT?
>
>On 18 Sep 2012, at 07:46, Mark Struberg wrote:
>
>> Hi Stu!
>>
>> +1, fully agree.
>>
>>
>> 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: Tuesday, September 18, 2012 12:22 AM
>>> Subject: Re: [cdi-dev] Subclassing?
>>>
>>>
>>>
>>> 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
>>>>>>>>
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