10:04 p.m.
On 02/21/2011 10:31 PM, Jason T. Greene wrote:
On 2/21/11 1:22 PM, Andrew Lee Rubinger wrote:
> Alongside our metadata discussions this morning, I'd like to offer up a
> prototype for use as the preferred metadata view for AS subsystems.
-snip-
> The purpose of the project is to define an object model for
> specification and JBoss-specific metadata, with the following driving
> tenets:
One of the problems of any kind of metadata project, is that the scope
is somewhat vague. It can be anything from just spec descriptors all the
way to the entire runtime state of server deployment. Without a clear
scope, it will likely feature creep towards the latter.
Exactly, the idea behind this one is to offer nothing aside from an
object view of spec metadata, along with import/export utils. Its scope
is intentionally limited. And as you've noted below, I gave an overview
of the proposed scope further down the email.
> * No compile dependencies outside the JDK
> * Pluggable backends (ie. DOM, XB, Stax, right now we use DOM and
> straight hardcoded parsing logic)
Why bother with pluggable backends? In particular whats the point of
having both a DOM parser AND a STAX parser?
The design is pluggable, but I've no plans slated ATM for any other
backends besides DOM. For instance Remy specifically mentioned StAX, so
if he were so inclined he could provide that backend and user code
wouldn't know the difference. Or, alternatively we could actually use
the existing jboss-metadata stuff as the backend, and use this as a user
view atop. Swapping out jboss-metadata later when we wanted.
> * Easy import/export to/from File/URL/String/Stream/bytes
>
> Other concerns are to be addressed at another level, namely:
>
> * Merging
> * Annotation scanning repo output> object model view
> * Validation
> * ...basically anything initiated during deployment.
This is a good start on specifying a scope. It sounds like an attempt to
do a saner JSR-88 framework.
JSR-88 is a weird beast. It's a deployment spec which also exposes out
deployment configuration for tooling?
The itch which lead to this project's inception was from the testing
community; users wanted to be able to mock out servlet configs in java
code, and send 'em off for deployment in ShrinkWrap.
But I think we could be well served to adopt it here as the agreed view
for AS subsystems. Because the API does little more than expose
spec/JBoss metadata grammars (and brings in no dependencies), I think
we've got a good chance of agreeing upon this model.
One of the challenges of using something like this for annotation
processing is the assumption that there is a one-to-one relationship
with annotations and configurable xml. This is not always the case. CDI
for example has a large number of annotations to process that are only
relevant to the actual CDI engine itself. This is not to say that there
could not be value in some kind of xml override mechanism (originally in
the draft specification), just that the consumers of interest are rather
limited (just weld cares about this information). Also you probably
don't want to have something that produces annotation java output.
This is a problem, but not one for the Descriptors project. What we'd
need here is a bridge between the annotation provider/index (I'm aware
of a few we've mocked up already) and the Descriptor model.
Annotation processor > index > bridge > Descriptor model
> Deployment logic should be, IMO:
>
> Deployer takes in deployment> Gen object model> calls outside layers
> for merging/validation/etc> deployer installs final view
That seems inline with what we have at the moment. The key thing though
is that a deployer's state be allowed to evolve at the same pace as the
deployer.
Can you expand on the "deployer state evolving" bit? I'm near certain
Descriptors wouldn't be imposing on anything here, but let's clarify?
S,
ALR