[webbeans-dev] Re: Producer fields on EJBs

[Pete Muir]

I thought through this some, and bounced ideas off Andy.

Gavin, I'm not sure that producer fields on SLSBs makes much sense -  
SLSBs instance state is undefined I think (some EJB expert correct if  
I'm wrong ;-). I think the spec should say that the behaviour of  
producer fields on SLSBs is undefined.

Assuming the above, I would still argue for a getFieldValue SPI that  
throws IllegalStateException if invoked on an SLSB reference - and I  
think this removes the issue Ken has with a many-to-one instances.

I'm slipping this for the upcoming release as we are too far from  
consensus.

On 6 Apr 2009, at 18:22, Pete Muir wrote:

>
> On 6 Apr 2009, at 18:00, Kenneth Saks wrote:
>
>>
>> On Apr 6, 2009, at 12:31 PM, Pete Muir wrote:
>>
>>> Carlo, Ken, Andrew,
>>>
>>> JSR-299 supports the notion of a producer field. By adding the  
>>> annotation @Produces to a field, you make it into a bean, which  
>>> can be used as the source of injections. The field can also be  
>>> associated with a scope. When you first look up an instance of a  
>>> bean, the field value is accessed, and stored in the context for  
>>> it's lifetime.
>>>
>>> As we deal with EJB references, we can't directly access the field  
>>> value (using reflection) so I think we should use the SPI here.
>>>
>>> I propose we add a method with this signature to the  
>>> SessionObjectReference we previously created for the purpose of  
>>> casting/removing EJBs https://svn.jboss.org/repos/webbeans/ri/trunk/spi/src/main/java/org/jboss/webbeans/ejb/api/SessionObjectReference.java
>>
>> There isn't necessarily a one-to-one relationship between an ejb  
>> reference and a bean instance.   For stateless session beans, any  
>> one of the bean instances can be used for any invocation.
>>
>> Can't this behavior be handled by the web beans interceptor?  By  
>> definition, each interceptor instance has the same life cycle as  
>> its associated bean instance, and the bean instance is available  
>> via the Interceptor InvocationContext.
>
> I did consider this, but not sure how to retrieve the result  
> invocationContext.getTarget() at the time it is needed for accessing  
> the producer field. We can't just store it from the construction  
> point onwards (serializability) and I can't see a way to access it  
> at some other point in the lifecycle - the only way to run an  
> @AroundInvoke is to call a method, and in this case which method  
> would you run, and how would you guarantee it has no side effects?
>
>>
>>
>>>
>>> /**
>>>  * Retrieve the value of a (possibly private) field
>>>  *
>>>  * @param field
>>>  *           the field to retrieve the value of
>>>  * @return the retrieved value
>>>  * @throws IllegalArgumentException
>>>  *            if the field doesn't exist on this session object  
>>> instance
>>>  */
>>> public Object getFieldValue(Field field);
>>>
>>> Any comments?
>>>
>>>
>>> On 29 Mar 2009, at 22:57, Pete Muir wrote:
>>>
>>>> Ok, I would think that some language in the spec to hint at this  
>>>> might be good, as instances of session beans elsewhere in the  
>>>> spec implies a EJB reference.
>>>>
>>>> On 29 Mar 2009, at 18:04, Gavin King wrote:
>>>>
>>>>> Yes, this is a good question - the 299 implementation would need
>>>>> direct integration with the EJB container for this. (Not the only
>>>>> place this is needed.)
>>>>>
>>>>>
>>>>> On Sat, Mar 28, 2009 at 7:18 PM, Pete Muir <pmuir at redhat.com>  
>>>>> wrote:
>>>>>> Hey
>>>>>>
>>>>>> Not quite sure how this is supposed to work as everywhere we  
>>>>>> hold a
>>>>>> reference (proxy) to the EJB, and therefore don't have access  
>>>>>> to the
>>>>>> instance and therefore can't get hold of the fields. Any  
>>>>>> pointers?
>>>>>>
>>>>>> Thanks!
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Pete Muir
>>>>>> http://www.seamframework.org
>>>>>> http://in.relation.to/Bloggers/Pete
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> -- 
>>>>> Gavin King
>>>>> gavin.king at gmail.com
>>>>> http://in.relation.to/Bloggers/Gavin
>>>>> http://hibernate.org
>>>>> http://seamframework.org
>>>>
>>>> --
>>>> Pete Muir
>>>> http://www.seamframework.org
>>>> http://in.relation.to/Bloggers/Pete
>>>>
>>>> _______________________________________________
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>>>> https://lists.jboss.org/mailman/listinfo/webbeans-dev
>>>
>>> --
>>> Pete Muir
>>> http://www.seamframework.org
>>> http://in.relation.to/Bloggers/Pete
>>>
>>
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>
> --
> Pete Muir
> http://www.seamframework.org
> http://in.relation.to/Bloggers/Pete
>
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--
Pete Muir
http://www.seamframework.org
http://in.relation.to/Bloggers/Pete