jsr366-experts@javaee-spec.java.net

[jsr366-experts] Re: Compatibility Problems with MR Resource Annotation Widening

From: Bill Shannon <bill.shannon_at_oracle.com>
Date: Tue, 03 Mar 2015 15:59:00 -0800

Jason Greene wrote on 03/02/15 14:34:
>
>> On Feb 27, 2015, at 5:38 PM, Bill Shannon <bill.shannon_at_oracle.com> wrote:
>>
>> Jason Greene wrote on 02/27/15 09:51:
>>>
>>>> On Feb 26, 2015, at 9:02 PM, Jason Greene <jason.greene_at_redhat.com>
>>>> wrote:
>>>>
>>>> So my recollection, was that this was intentional since the bindings
>>>> arenít useful to CDI applications, and you could always reference
>>>> another binding defined by a component which did support it, if you
>>>> needed such behavior. The deployment descriptor for CDI doesnít allow
>>>> you to override these bindings, and the other deployment descriptor
>>>> locations donít cover the full set where @Resource can appear (for
>>>> example ejb-jar overrides are defined on ejb components and not
>>>> globally). Finally, @Resource (and the other EE bindings) can only
>>>> appear on producer fields, which is a subset of what 250 defined.
>>>>
>>>> Iíll ping Pete to see if he remembers the same, but yeah I agree the
>>>> combination of the specs implies that it should work, other than the
>>>> fact that it canít work the way the global rules are defined.
>>>
>>> BTW I confirmed that this matched Petes understanding as well.
>>>
>>> There was never any interest for CDI managed beans to support:
>>>
>>> - Creation of @Resource (et al) JNDI Bindings - Usage of @Resource (et
>>> al) Class declarations - Usage of @Resource (et al) Method injection
>>>
>>> These all have no benefit to CDI applications because they are all
>>> superseded by other constructs. The annotations were just reused for the
>>> ties just to avoid creating new ones.
>>
>> Except that there's nothing anywhere in the spec that says in this
>> specific case you don't have to create the bindings that the spec says you
>> have to create. And for all the reasons described previously, we would not
>> want the spec to say that.
>
> My point is that even if you added in the bindings the semantics are still
> different. You arenít really using EE injection (in the traditional sense)
> when you define @Resource on a CDI bean.

I don't know why you say that. There's nothing in the spec that says in
this one special case you don't have to do what you have to do in all the
other cases. The reason this case is supposed to work is because the
container is handling it just like all the other cases, including creating
a JNDI entry and including allowing you to override that entry using a
deployment descriptor.

> You are instead defining a CDI field
> producer that does a resource lookup. In fact if you just renamed "@Produces
> @Resource" to be ď@Produces @JNDIObject", this confusion likely would have
> never occurred.

Because that would've been a different spec with different semantics.
Maybe that's the spec that some people wanted, but that's not the spec
we have.

> You could add full Java EE injection to CDI managed beans, but itís a lot of
> spec work that would serve little purpose. The whole point of CDI is to offer
> a strong type-safe injection mechanism, and for that reason CDI forces you to
> minimize your usage of @Resource to a single location that is then @Inject-ed
> where needed. If we defined the rest, we would end up saying ďHey this never
> worked before. We made it work now, but still donít use it.Ē

There's nothing that says you can only use resource injection in this
special way. It's simply a combination or two existing capabilities,
with no special cases needed. The Java EE container fills up the field
with the injected resource reference. CDI doesn't know or care how that
happens. CDI uses the value of that field for @Produces. Java EE doesn't
know or care how the value of that field is used. That was the beauty of
combining these two existing capabilities. We defined Java EE resource
injection to work for CDI managed beans so that we could combine these
two features without either having to know about the other.

> Iím hoping we keep the scope limited by either letting CDI have its own
> semantics, or we change it to define bindings consistent with EE resource
> injection and stop there.

It's kind of late to back out of what we defined some time ago. We're
definitely not going to change the semantics of @Resource so that it works
differently in some cases.

>>> In an early CDI draft there was a complete xml description language in
>>> beans.xml that could be used to override/define all aspects of CDI
>>> managed beans (including annotations). However, that was dropped since
>>> portable extensions allowed third party definitions of such a thing.
>>
>> I only ever expected that to be able to change how @Inject worked, not
>> change how @Resource worked, since @Resource was defined by the platform
>> spec and not the CDI spec.
>>
>>> The bindings, if desired for consistency purposes, could be addressed by
>>> the EE spec, and the existing CDI RI looks like it already can support
>>> that. Class declarations could likewise be addressed, but would probably
>>> require some CDI RI SPI improvements. Method injection on the other hand
>>> probably would require CDI spec involvement.
>>
>> The platform spec clearly requires that these bindings are created,
>> always.
>>
>> If you extract all the annotation information from an application using
>> whatever technique you think is correct, turn it into the corresponding
>> deployment descriptor information, merge it into the deployment
>> descriptors, set metadata-complete, and remove all the annotations from the
>> application, will the behavior be the same? It should. That was clearly
>> our intended design when we introduced these annotations and extended the
>> deployment descriptors to allow injection to be specified.
>
> If you use any element of CDI in your application (whether @Resource is done
> by CDI or by something else, or not used at all) then no. CDI does not define
> an xml format that can substitute all usage of its annotations. You could do
> it with a portable extension that defined one though.

metadata-complete has no effect on CDI. But you absolutely must be able
to use CDI with an application that also uses metadata-complete. You'll
still need to use the CDI annotations, since CDI doesn't provide an XML
equivalent, but all of the Java EE resource references and definitions
and injections can be specified in the deployment descriptor instead of
using the corresponding annotations.

It's been a design goal of all of the Java EE resource annotation support
(but not of *all other* annotation support), that everything you can do
with these annotations you can also do with the deployment descriptors.
This lets you convert the annotations into deployment descriptor entries,
set metadata-complete, and then customize the resource information without
changing the application.