[seam-dev] Seam 3 porting issues

[Pete Muir]

On 2 May 2009, at 04:24, Dan Allen wrote:

> Before I get started, I want to mention that we should have wiki  
> pages up to discuss the status (Jay is doing this with RichFaces and  
> it is working out nicely). I'll duplicate some of my response there.
>
> On Wed, Apr 29, 2009 at 8:17 PM, Shane Bryzak  
> <shane.bryzak at jboss.com> wrote:
> To get the ball rolling, I've hand picked a couple of the more  
> important issues from my list.  We can discuss these in more depth  
> during the conf call, however I would like people to start thinking  
> about them now.
>
> 1. Obtaining instances to a Web Beans component from outside of the  
> component framework.  There are a number of places that we need to  
> do this.  I got around it in SeamLoginModule by extending the  
> CallbackHandler to support callbacks for Identity, Authenticator,  
> etc.  We unfortunately don't have such an easy workaround in other  
> places - here's just a few examples:
>
>  * DroolsHandler (which is a jBPM handler) needs to access the  
> Expressions and WorkingMemory components.
>  * SeamGlobalResolver (which resolves Drools global variables) needs  
> to get an instance of Manager to perform lookups.
>  * EntitySecurityListener and HibernateSecurityInterceptor both  
> require access to security components.
>  * DateConverter needs to access the TimeZone and Locale components
>
> The 299 spec guarantees that the Manager will be available in JNDI.  
> So that is our bridge.

This is problematic as it's only guaranteed for EE, for example by  
default in TC it's not available. The better hook is to observe the  
startup event.

> The question becomes, should we cache the result of this lookup. We  
> can either do a thread locale cache...which is fine since a single  
> JNDI lookup per request is very cheap.

If the lifecycle of the place you need to propagate it is well defined  
(i.e. you know it will occur next in the current thread) this is safe,  
but sometimes this isn't well defined.

> We could, however, think about putting it in application-scope since  
> it shouldn't change between deployments. For that, we would need  
> access to the servlet context application scope which would mean  
> having a seam-contexts module. Anyway, I have an impl already. See  
> JndiManager in the seam-faces module. It can be changed to use a  
> thread local.

I would avoid this. If you are in a bean then inject it using @Current  
Manager manager, if you are in a non-bean, you need to decide this  
case by case, depending on the lifecycle of the object.

> One possible solution to this issue is to have a thread local  
> Manager available for the lifecycle of a single request, which can  
> be accessed by non-component classes.

Again, I would avoid this - why do you need to do this? It is also  
potentially dangerous with async requests where you can have the same  
thread sequentially processing different requests before they end.

In general, don't make assumptions about JNDI, or that you are in  
servlet.

I've said it before, and I'll say it again. There is no global pattern  
to solve this, we have to address this for each case.

>
>
> 2. Module granularity / dependencies.  I'm going to use security as  
> an example for this issue, however there are other modules which are  
> similarly affected.  Within the security module, there are certain  
> features (such as the action components, RememberMe, etc) that  
> depend on the faces module.  My preference is to not have any  
> dependencies on faces and that the security module remains view- 
> layer independent.
> One possible way to solve this issue is to introduce a bridging  
> module, in this example it would be seam-faces-security which  
> contains the functionality that you would require if you were using  
> Seam Security in a JSF environment.  The only downside to this is  
> that it may lead to jar bloat (which may not really be an issue).   
> The upside is that it keeps everything nice and modular, and helps  
> to simplify the dependency tree.

I think this is the correct approach. We can then provide a seam-jsf  
jar that bundles *all* JSF related seam modules, and people can dump  
that in their WEB-INF/lib to get going. As their project develops,  
they can pick up individual modules as they want.

>
> Remember there is a difference between compile time and runtime  
> dependencies. It may be necessary for seam-faces to depend on seam- 
> security for compile, but if you don't have seam-identity deployed,  
> the the observer never get called. The other line of thought is that  
> security is so central that seam-faces should depend on it. We'll  
> just keep moving things around until it feels right.

This is another good option.

>
>
> -Dan
>
> -- 
> Dan Allen
> Senior Software Engineer, Red Hat | Author of Seam in Action
>
> http://mojavelinux.com
> http://mojavelinux.com/seaminaction
> http://in.relation.to/Bloggers/Dan
>
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--
Pete Muir
http://www.seamframework.org
http://in.relation.to/Bloggers/Pete