You'll find below my feedback on Generic Beans in Seam Social (at last)
What I need is an easy way to create automatically a bunch of beans when a bean
with a given annotation is declared (i.e. triggers implicit creation of
associated beans). This solution make my task easier than declare a bunch of
producer but also will ease the work of third party developers when they'll
create a new module for a new Social Service.
In my OAuth use case I have a collection of beans created by the
OAuthApplication generic annotation. This annotation has to be put on an
OAuthService bean and contains information needed by all user to use this
application (mainly consumer key and secret key).
The beans created the generic beans mechanism are
- an OAuthService with basic methods to deal with Oauth requests. It is
Application Scoped.
- an OAuthserviceSettings which contains data about the the service (data
retrieve from OAuthApplication annotation), it's also Application Scoped
- an OAuthProvider which contains low-level methods for OAuth encryption and
hide the concrete implementation which today is a third party library :
scribe-java. It's also application scoped
- an OAuthSession which contains data for a given user : OAuthToken
and identity information cache. It's Session scoped.
So with this line of code :
@OAuthApplication(apiKey = "FQzlQC49UhvbMZoxUIvHTQ", apiSecret =
"VQ5CZHG4qUoAkUUmckPn4iN4yyjBKcORTW0wnok4r1k")
@Twitter
@Produces
@ApplicationScoped
TwitterBaseService twitterService;
I create 4 beans with the @Twitter Qualifier and different scopes. When a 3rd
party developer adds a new service, she has to create a new Qualifier
(@LinkedIn for instance) a service bean managing calls to this service and
that's all.
Now I had some issues with Generics. The main one is the documentation which is
far from being up to date. I watched code and tests to figure out how it was
suppose to run and I have to admit the code seems very complex (I'm not sure to
figure out exactly how it does its magic). Last issue is more a CDI one but
with Generics it becomes obvious : the difficulty for a bean to dynamically
retrieve its qualifier(s) when its not in the depends scope (in that case
@InjectionPoint does the job). To make short Generics would be better with more
introspection tools for bean.
IMHO the concept behind Generics should be kept in DS but the implementation
and usage should be simplified if possible.
regards,
Antoine
Le 7 mars 2012 à 16:55, Pete Muir a écrit :
> Yes, we need a new name for the feature, generic beans isn't good ;-)
>
> I'm not sure Bean Groups is right, any other ideas?
>
> On 7 Mar 2012, at 02:13, John D. Ament wrote:
>
>> @pete
>>
>> Reminds me of the JMS issue we have.
>>
>> So I suppose - could we rename the feature - "Bean Groups" ? Then describe
>> the feature more along the lines of "the ability to define a bean that
>> contains producers that inherit the qualifiers of the existing injection
>> point.
>>
>> John
>>
>> On Tue, Mar 6, 2012 at 5:47 AM, Pete Muir <[email protected]> wrote:
>>
>>> It's probably fair. They are certainly missing some things you might
>>> expect, that Antoine ran into…
>>>
>>> If we can find a way to create a similar extension capability but
>>> implemented differently, it would be good. However what they offer is too
>>> useful to pass up.
>>>
>>> You often have a situation where you want to create the effect of having a
>>> group of beans for a multiple configurations of something. Injection of
>>> InjectionPoint can go some way to solving this, but suffers from three key
>>> limitations. Let's first take an example problem domain which I know well -
>>> caches, specifically Infinispan.
>>>
>>> You obviously want to be able to configure multiple caches in an
>>> application, as they might well have different characteristics, such as
>>> eviction policy, persistent storage, and so on.
>>>
>>> Infinispan offers a number of caching classes associated with a cache - a
>>> Cache interface, and an AdvancedCache interface, as well as the
>>> Configuration for the cache. We want to be able to inject any of these
>>> objects for each cache configured. e.g.
>>>
>>> @Inject @Cache("cache1") Cache cache;
>>> @Inject @Cache("cache1") AdvancedCache cache;
>>> @Inject @Cache("cache1") Configuration cache;
>>>
>>> @Inject @Cache("cache2") Cache cache;
>>> @Inject @Cache("cache2") AdvancedCache cache;
>>> @Inject @Cache("cache2") Configuration cache;
>>>
>>> The first problem we can see here is that we've lost type safety. This is
>>> quite easy to fix, simply by having the user create an annotation per
>>> cache, which perhaps could be meta-annotated with the name of cache. We now
>>> have (truncated for brevity!)
>>>
>>> @Inject @Cache1 Cache cache;
>>>
>>> However, now let's assume we are running in JavaSE, and we need to don't
>>> have something like JNDI to look up the CacheManager in, every time we want
>>> to access a cache. We need to make the beans that hold the cache reference
>>> application scoped. This is the first of the key problems I identified
>>> above.
>>>
>>> We could solve this by saying that the cache manager is stored in
>>> application scope, and the cache is looked up each time, but it's also
>>> reasonable to assume that there can be multiple cache managers in an
>>> application.
>>>
>>> The second problem, is that we really still need a way to attach a
>>> configuration to a cache. A producer method is an ideal way to do this
>>> (produce the configuration needed for the cache, so that CDI can pass it to
>>> Infinispan at the right point), but we somehow need to associate this
>>> producer method through, and have CDI know how to call this. Qualifiers of
>>> course solve this.
>>>
>>> Finally, we of course want this properly validated at startup, and we do
>>> know the entire system at startup.
>>>
>>> I hope that outlines some of the problems we wanted to solve with generic
>>> beans. Anyone have a better idea how to solve this? I'm all ears :-D
>>>
>>> On 4 Mar 2012, at 20:01, Mark Struberg wrote:
>>>
>>>> I don't think it's correct to call them buggy. It's just that it might
>>> be _very_ hard to provide the same behaviour over all our supported
>>> containers.
>>>> But we will hit those kind of compat problems sooner or later anyway and
>>> will need to find a way to deal with them.
>>>>
>>>>
>>>> LieGrue,
>>>> strub
>>>>
>>>>
>>>>
>>>> ----- Original Message -----
>>>>> From: Antoine Sabot-Durand <[email protected]>
>>>>> To: [email protected]
>>>>> Cc:
>>>>> Sent: Sunday, March 4, 2012 8:38 PM
>>>>> Subject: Re: [DISCUSS] DELTASPIKE-14 GenericBeans
>>>>>
>>>>> T hank you John to launch this subject. I've been very busy since
>>> january and
>>>>> didn't found time to launch the subject. To be totally honest I thought
>>> I
>>>>> was the only one interested in them.
>>>>>
>>>>> Now regarding Generic beans in Solder :
>>>>>
>>>>> - documentation is quite inaccurate
>>>>> - they are bugy : I didn't had bug, but it seems that some their tests
>>>>> don't pass
>>>>> - I read some wrong information about them : you can't create beans in
>>>>> another scope that the generic bean definition.
>>>>>
>>>>> I'll prepare a description of how I use them in Seam Social to ease
>>>>> extension of the framework and the issue I encounter using them.
>>>>>
>>>>> regards,
>>>>>
>>>>>
>>>>> Antoine SABOT-DURAND
>>>>>
>>>>>
>>>>> Le 4 mars 2012 à 18:27, Jason Porter a écrit :
>>>>>
>>>>>> I think they're really powerful, but we may need to do some rewrite to
>>>>> make sure it works correctly in a modular container.
>>>>>>
>>>>>> Sent from my iPhone
>>>>>>
>>>>>> On Mar 4, 2012, at 8:52, "John D. Ament"
>>>>> <[email protected]> wrote:
>>>>>>
>>>>>>> Hi All
>>>>>>>
>>>>>>> I would like to begin discussing the use of Generic Beans from Solder
>>>>>>> (currently this issue is assigned to Antoine, but I have some
>>> bandwidth
>>>>> and
>>>>>>> offered to help him here). This feature is used to configure a set of
>>>>>>> related beans that require shared components, while still allowing
>>>>> scopes
>>>>>>> to be provided. This is useful when trying to make legacy
>>>>> libraries/APIs
>>>>>>> CDI capable. The following are the API components required for
>>>>>>> GenericBeans:
>>>>>>>
>>>>>>> - @GenericType(Class<?> clazz) - defines the type of
>>>>> configuration for the
>>>>>>> generic. This annotation is placed on another annotation, as defined
>>>>> by
>>>>>>> the application developer or framework author to support how
>>>>> configuration
>>>>>>> is resolved. This will look for a matching bean of the given type and
>>>>>>> resolve it based on the annotation that this is assigned to.
>>>>>>> - @Generic - when using the manager type, defines an expected
>>> injection
>>>>>>> point for a generic bean.
>>>>>>> - @GenericConfiguration(Class<?> clazz) - defines the
>>>>> relationship between
>>>>>>> generic objects.
>>>>>>> - @ApplyScope - indicates that the produced object should inherit the
>>>>> scope
>>>>>>> of the configuration.
>>>>>>>
>>>>>>>
>>>>>>> The examples in the Solder documentation describe this in depth:
>>>>>>>
>>>>>
>>> http://docs.jboss.org/seam/3/3.1.0.Final/reference/en-US/html/solder-genericbeans.html
>>>>>>>
>>>>>>> Thoughts/questions on the feature?
>>>>>>>
>>>>>>> john
>>>>>
>>>
>>>
>
