[cdi-dev] Subclassing?
Pete Muir
pmuir at redhat.com
Tue Sep 18 10:34:40 EDT 2012
On 18 Sep 2012, at 15:31, Mark Struberg wrote:
>
>
> 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?
Stuart is the best person to ask.
>
> 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
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> cdi-dev mailing list
>>>>>>>>> cdi-dev at lists.jboss.org
>>>>>>>>> https://lists.jboss.org/mailman/listinfo/cdi-dev
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>>
>>
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