Hi, all.
I think extending CDI stereotypes is good and the right way to go.
Sorry for late feedback.
--
--------------------
Software Innovation Evangelist
Researcher & Executive Director / WAS Lab / TmaxSoft R&D Center
PGP http://www.javadom.com/personal/yoonforhatgmaildotcom.asc
2012. 9. 21., ¿ÀÈÄ 3:56, Bill Shannon <bill.shannon_at_oracle.com> ÀÛ¼º:
>
> As with my previous message, I'd like to hear from the rest of the
> expert group on this topic.
>
> Bill Shannon wrote on 08/30/2012 01:58 PM:
>> Some time ago David Blevins started a discussion in the EJB expert
>> group about "meta-annotations". The thread starts here:
>> http://java.net/projects/ejb-spec/lists/jsr345-experts/archive/2011-12/message/21
>>
>> Several of us have been discussing this idea privately on and off
>> for some time, and it's time to bring that discussion to this expert
>> group. The general idea is to allow developers to create their own
>> annotations that are combinations of existing annotations. You can
>> think of this as a limited "macro" facility for annotations.
>>
>> For example:
>>
>> @Metatype
>> @Stateless
>> @TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
>> public @interface NonTransactional { }
>>
>> @NonTransactional
>> public class MyStatelessEJB { ... }
>>
>>
>> This is essentially CDI stereotypes, which leads to a counter-proposal
>> to simply allow CDI stereotypes to be used more widely.
>>
>> The issues with using stereotypes more widely are:
>>
>> - Stereotypes are implemented by CDI, but (typically) the Java EE
>> deployment processing has no knowledge of CDI when it's looking
>> for Java EE annotations. Integrating with CDI so that stereotypes
>> could be considered during this deployment-time annotation processing
>> would require a new CDI SPI.
>>
>> - CDI extensions can change the definition of a stereotype. Because
>> most Java EE annotations are processed at deployment time, before
>> any application code (including CDI extensions) can run, any dynamic
>> changes to stereotypes can't effect the deployment process.
>>
>> - The additional processing required at deployment time to handle
>> stereotypes could have a non-trivial impact on deployment performance.
>>
>> To address these issues, we could introduce a new @Metatype annotation
>> with most of the same functionality as stereotypes, but without the
>> ability to change them dynamically. Of course, introducing a new
>> annotation has issues of its own:
>>
>> - Developers will be confused as to when to use @Stereotype and when
>> to use @Metatype. In most, but not all, cases they will behave
>> similarly.
>>
>> - Introducing a new annotation, without a common place to handle
>> processing of that annotation, will likely lead to inconsistencies
>> in its implementation.
>>
>>
>> Our preliminary analysis suggests that the performance impact of
>> handling stereotypes when processing deployment time annotations
>> will not be significant. While there's a very small incremental
>> cost to be *able* to handle stereotypes, most of the actual cost
>> is only incurred if applications *use* stereotypes. And in any
>> event, the cost would be essentially the same as the @Metatype
>> approach.
>>
>> Based on our experience so far, very few developers make use of the
>> dynamic capabilities of stereotypes. That fact, along with the
>> potential confusion of having two annotations that are almost but
>> not exactly the same, makes it attractive to consider enhancing
>> the definition of stereotypes to indicate that when they're used
>> with Java EE annotations, the definition of the stereotype is static
>> at deployment time. Of course, this also requires a tighter
>> integration of CDI with the rest of the Java EE platform, which
>> seems to be the direction we're moving on several fronts. (More
>> on that later.)
>>
>> Using stereotypes for this purpose would only work when CDI is
>> enabled. Separately, the CDI expert group is considering whether we
>> should change the default and enable CDI by default. Doing so would
>> make this approach more attractive, although it may also introduce
>> additional performance issues that would need to be addressed.
>>
>> Allowing the use of stereotypes for this purpose requires changing
>> many existing annotations to include ANNOTATION_TYPE as a @Target.
>>
>> Many existing implementations would need to be changed to understand
>> how to expand stereotypes. Requiring every technology to do this
>> itself will almost certainly lead to inconsistencies. Since stereotypes
>> are a CDI feature, CDI will provide a simple replacement for the
>> java.lang.reflect methods such as getAnnotations that takes into
>> account stereotypes.
>>
>> Some technologies will not want to have a hard dependency on CDI so
>> we'll need to provide a simple way for them to conditionally invoke
>> these new methods only if CDI is present, falling back to java.lang.reflect
>> if not. This seems straightforward. In this case, the functionality of
>> @Stereotype would not be available to applications that chose to run
>> without CDI.
>>
>> What do you think of the above approach? Is expanding the use of
>> @Stereotype the best approach? Or are the issues with that approach
>> significant enough that we should consider introducing a new annotation
>> for this purpose?
>>
>