Reza,
I have some comments inline.
On Tue, Aug 30, 2011 at 4:58 PM, Reza Rahman <reza_rahman_at_lycos.com> wrote:
> John,
>
> Overall, I think the @Inject support for JMS 2 proposal is a good start.
> The way I see it, we should focus on getting this right before spending too
> much time considering the other approaches since it is the least intrusive
> and most flexible.
>
> Specific concerns below that we could discuss further (tried hard to be as
> concise as possible - please ask follow-up questions):
>
> * I think we should avoid making this CDI specific as much as possible. I
> think all of this can really be done by just sticking to the javax.inject
> APIs and concepts. We could add a comment in the spec that these features
> would be implemented using CDI in a Java EE environment. In terms of the
> TCK, it might be necessary to use META-INF/beans.xml to trigger injection.
> It would have been nice to just be able to use @Resource for this, but the
> issue is that @Resource does not have much flexibility in terms of adding
> the additional meta-data that would be needed for this (it is also not that
> readable as compared to the more general purpose @Inject and might be
> treated as "legacy" in most Java EE 6 applications). The big benefit to
> sticking to JSR 330 is that non-CDI containers like Spring and Guice could
> still implement this API as could some JMS providers that would support
> these features in Java SE (in non-standard ways) and still not require a CDI
> container. It is also the case that Spring already supports concepts like
> the transaction scope that could be leveraged to make this approach scalable
> in a server-side environment (more on that below).
>
Unfortunately, I don't think there's much we can provide if it's only
JSR-330. Would we then require JMS implementations to support the Provider
interface for all injectable interfaces?
>
> * I'd rather not add the AcknowledgeMode enumeration. If the JMS API were
> designed today, this is the route we'd likely go, but adding this now
> introduces a potentially confusing redundancy that really does not provide
> much practical value right now.
>
This relates back to a note that Nigel had passed around. the existing
methods would need not be modified, but new methods could potentially use
the enum. Plus, in this case we can make more type safe. Perhaps the enums
would have int values and the necessary translation capabilities.
>
> * @JmsCredentials is not really very appropriate in a Java EE environment
> where such configuration would likely be specified at the container/resource
> level.
>
>
Agreed, would only be useful in SE.
> * I don't think MessageFactory is needed at all if we simply allow for
> injecting proxied, transaction-scoped message sub-types and enhancing
> message producers/consumers to directly handle Objects (in fact, a major
> goal of DI is to avoid such factories/resource look-ups). I detailed such a
> mechanism in my initial write-up of this approach. I do know Seam JMS does
> not support this today in part due to the session/message coupling ambiguity
> but we could simply get that ambiguity cleared up for JMS 2 instead of
> introducing a potentially redundant API.
>
>
So I was thinking about this a bit more through the hurricane. I decided
that the method belongs best at the ConnectionFactory level. I thought
about injecting messages as you had said when we met up, I don't know if it
will work well in a multiple implementation environment.
> * I don't think JmsDestinationLiteral, JmsConnectionLiteral or
> JmsCredentialsLiteral are needed at all. Where additional programmatic
> flexibility is needed, it is sufficient to simply inject and/or look-up
> higher level JMS objects/resources like connection factories, destinations,
> connections and sessions. The look-ups would be performed via JNDI just as
> they are done today. Introducing these also creates a CDI dependency that
> can be avoided.
>
>
One issue I know the seam guys ran into was that no literals were provided
out of the box. From my perspective, I think the literals should be
provided just to make it one last thing that doesn't need to be boilerplate
code.
> * ConnectionProducer seems to be a CDI specific implementation detail that
> can be avoided in favor of JCA pluggability and existing Java EE container
> defaults. I think this not really needed.
>
It's one example, we could require a CDI extension that injects as well.
Don't know if we even want to provide concrete classes in the api at all at
this point, but I think it would make some things a bit easier.
>
> * The implicit conversion is definitely a good idea the way I see it. I
> think it should be supported for both sending and receiving messages. I did
> mention this in my JMS utility API proposal too.
> * I think all usable non-deprecated JMS objects including messages,
> temporary queues/topics and connection meta-data should be injectable, not
> just connections, sessions, message producers, message consumers and queue
> browsers. This would be pretty easy to implement and add to usability. Now,
> I do understand that this is not what is currently in Seam JMS. Is the
> difficulty here the reliance on CDI producers as opposed to creating custom
> proxies or is this just a simple oversight?
>
> * I don't think @JmsConnection, @JmsDestination, etc need be qualifiers.
> They can simply be plain annotations. Making them qualifiers adds a needless
> dependency and I can't think of a case where it is actually necessary to use
> these annotations as qualifiers?
>
This goes back to the other side of my proposal. They won't need to be
here, however for events to work they need to be.
>
> * The issue of correct scoping for the injected JMS objects is pretty
> critical to guaranteeing scalability across different container
> implementations/applications/**environments. I do know that Seam JMS
> currently has these injected objects in the dependent scope, in part because
> there is not yet a standard @TransactionScoped for CDI as of yet. The
> problem is that having these objects in the dependent scope will eventually
> cause the connection pool to run out if the objects are injected into very
> long-lived objects such as Servlets, pooled stateless session beans,
> singletons and application scoped services. This is basically the opposite
> problem of the connection thrashing that happens with Spring JmsTemplate.
> JPA avoids this problem by making the persistence context transaction scoped
> by default and caching underlying logical sessions/connections per
> transaction (and limiting the extended persistence scope option to stateful
> session beans). We can specify the same thing for injected JMS objects in
> addition to specifying inter-dependencies for intermediate JMS objects to
> maximize resource re-use. For reference, I outlined the solution that we had
> for Resin in my initial detailed proposal. Now, implementing transaction
> scoped resources does typically require some vendor-specific code to
> interact with the underlying transaction manager. This can be modularized
> very easily just as is done for EclipseLink as well as JBoss/Hibernate (I am
> sure the folks responsible for that code base could easily help us if
> needed). We also have a @TransactionScoped annotation implemented in Resin
> that might help here. As such, this could be specified without explicitly
> specifying CDI either and just sticking to JSR 330.
>
I'm not against using a standardized scope, but this sounds like something
that we need to get clarified at the platform level or within CDI.
>
> Hope this makes sense. Is it a good idea to have another conference call to
> sort some of this out? Alternatively or in addition to, I am happy to meet
> in person again as well.
>
> Cheers,
> Reza
>
>
>
> On 8/17/2011 9:40 AM, Nigel Deakin wrote:
>
>> Many thanks, John, for your work in drafting these documents. I look
>> forward to reading them.
>>
>> I think sending these round as attachments is fine for now. This allows
>> the expert group, and subscribers to the user alias, to read them. Please
>> use this email thread for questions and comments. I'm sure I will have some
>> of my own soon.
>>
>> I agree with John that we should seek comments as soon as possible, so
>> please respond within two weeks, after which I hope we can draw some general
>> conclusions as to what the next step should be. In addition to any more
>> detailed comments, please think about the higher-level topics, such as
>> whether you agree with the general direction taken by each document or
>> whether you would prefer a different direction. Please consider the
>> implications for both SE and EE.
>>
>> I think the way John has presented this as to separate documents is very
>> helpful. To help us all manage the comments that are made, I suggest we
>> submit our comments on each document separately.
>>
>> Use *this* thread ("JMS Support for DI") to discuss John's first document
>> (JMS Support for AtInject).
>>
>> I'll start another thread to discuss John's second document "JMS 2.0 Event
>> Messaging".
>>
>> If you have questions about the DI/CDI technology itself, ask them in
>> either thread. I'm sure the rest of us would be interested as well.
>>
>> (I appreciate I'm being a bit prescriptive about email subject lines, but
>> it really does help me ensure that every comments gets considered properly,
>> especially when I go back to old threads which I intended to do shortly)
>>
>> Nigel
>>
>>
>>
>>
>>
>> On 17/08/2011 02:14, John D. Ament wrote:
>> > Hello All,
>> >
>> > Attached are documents containing my proposal for CDI support in JMS
>> 2.0. There are two documents:
>> >
>> > 1. JMS2.0AtInjectSupport - this document describes basic injection
>> capabilities that are desirable to JMS 2.0. These
>> > injection capabilities allow for the injection of the standard JMS
>> client APIs into any managed object within a bean
>> > archive. This document also describes some minor API changes that I
>> believe would help simplify development.
>> > 2. JMS2.0EventMessaging - this document describes a mapping process
>> from POJOs to JMS Messages, usage of the CDI Event
>> > model API to send events that were observed as JMS messages to
>> specified destinations and to handle incoming JMS
>> > messages as CDI events.
>> >
>> >
>> > I started to put these up on the wiki, however the formatting support in
>> the wiki doesn't seem to be there for how I was
>> > looking to structure the documents, but I'll work on getting them in; I
>> really wanted to get the documents out there as
>> > I work with the wiki. I recommend reading these documents in the
>> numbered order as listed in this email. I tried very
>> > hard to not make them dependent on one another, however there are some
>> shared contents between them. It makes sense to
>> > support both if either is chosen for support, however there is no
>> required behavior between the documents that is no
>> > touched upon by both. I'm not sure what the process should be for
>> review, but I figure we should set a time limit on
>> > the review period, maybe 2 weeks? (Nigel, I hope you can provide some
>> feedback on a timeline, since one of the issues we
>> > noted on the call was a time frame for draft). I assume all comments
>> should be posted back to the EG, If anyone would
>> > like to ask me specific questions related to CDI, I assume it's fine to
>> ask directly. As a note, these should be
>> > considered in parallel to Reza's documentation on a Spring-styled API.
>> >
>> >
>> > Regards,
>> >
>> > John
>>
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 10.0.1392 / Virus Database: 1520/3835 - Release Date: 08/15/11
>>
>>
>>
>