On Tue, May 26, 2009 at 11:59 PM, Dan Allen <dan.j.allen(a)gmail.com> wrote:
What I realized is that StatusMessages are really a generic repository that
should be updated and consumed by the framework-specific activity.
Therefore, it seems to me like there should be one and only one
conversation-scoped StatusMessages. Then, if you want to have some extra
methods for convenience (for instance in JSF to add a StatusMessage from an
existing FacesMessage) you create a class which extends and wraps the
StatusMessages component (StatusMessages would be injected into it and all
overrides delegating to it). You could also override the onBeforeRender()
method where you might put the logic for converting and transfering to the
native message type and storage. The executor of that conversion would be
implemented in the framework-specific listener.
For instance, 9 out of 10 times you simply inject the StatusMessages to use
in your application:
@Current StatusMessages statusMessages;
For JSF, there is a FacesMessages bean which inherits from StatusMessages
(to keep the API the same) and delegates calls to the StatusMessages
instance. It also adds the logic to create FacesMessage objects in the
onBeforeRender() method
public void onBeforeRender() {
super.onBeforeRender();
// create FacesMessage objects and register them here
}
The ConvertStatusMessagesListener (a JSF system event listener) executes
the onBeforeRender() call.
manager.getInstanceByType(StatusMessages.class, new
AnnotationLiteral<Faces>() {}).onBeforeRender();
There are also some convenience methods on the FacesMessages instance. If
you want to use them, you inject as follows:
@Faces FacesMessages facesMessages;
I can't use @Current here because otherwise the resolution would be
ambigous. I could just clone the StatusMessages API in the FacesMessages
class to avoid having to use this binding type, so if you have a
feeling/advice there, I would be glad to here it.
This approach seems fine to me, but I also wonder if composition might be
better than inheritance in this case, i.e. StatusMessages is framework
independent and not specialized, and provide a separate component subclassed
by each framework that propagates the contents of StatusMessages into the
view. Most code that injects StatusMessages only wants to add to it
messages to it, and the only code that wants to render those messages is in
the view framework glue, so they seem like separate concerns. The only
reason I didn't go this route in my mods to Seam2 was to minimize changes
for backward compatibility.
Okay, that's one approach. Now for something different. There is a similar
specialization w/ the Expressions class (an EL convenience API). If working
within the JSF request, we want to override some methods so that the bean
uses the current JSF EL context. In this case, I decided to try Clint's
approach described in the cited issue report.
That approach also looks fine to me, although I should note that with regard
to your specific example, Wicket has no notion of Expressions, and so
wouldn't specialize it. Wicketeers don't go for EL, as we have nothing that
isn't in java :)
Now that s/Manager/BeanManager/ is view agnostic, and once StatusMessages is
refactored as above, I'm not sure there's a use case for the
RuntimeSelectedBean mechanism. Well, yet :)
-Clint
A producer method will locate beans that have the binding type
@RuntimeSelected and will consult the isActive() method to determine which
one is prepared to handle the current request. The isActive() method comes
from the RuntimeSelectedBean interface. So the bean must have both the
binding type and the interface. There is a second binding type, @Default,
which indicates which implementation should be used when there are no
@RuntimeSelected implementations present or active. It is mutually exclusive
with @RuntimeSelected.
So you have:
public @Default class Expressions { ... }
public @RuntimeSelected class FacesExpressions extends Expressions,
RuntimeSelectedBean {
public boolean isActive()
{
return FacesContext.getCurrentInstance() != null;
}
}
public @RuntimeSelected class WicketExpressions extends Expressions,
RuntimeSelectedBean {
public boolean isActive()
{
return Application.exists();
}
}
The producer type for the Expressions bean is application-scoped and the
producer method is dependent-scoped (or request-scoped?). The available
instances are looked up when the producer is initialized and the instance is
selected from this set each time the producer is resolved.
Of course, I could have used this strategy for the StatusMessages too,
except in the case of StatusMessages it is logical to use the shared/generic
StatusMessages bean. It's only when you need to convert the messages do you
need the specialization and therefore I think we can avoid having to do the
runtime selection.
I've committed all of this to the Seam trunk if you want to check it out.
I'm open to suggestions...I'm just trying to get used WB and find a workable
approach. The solutions we decide on are important because the define a
standard practice we will follow as more cases arise.
-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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Clint Popetz
http://42lines.net
Scalable Web Application Development