I think that Arjan's explanation sounds solid. Having one less attribute
to worry about would certainly make things easier for those getting started.
Best
Josh Juneau
juneau001_at_gmail.com
http://jj-blogger.blogspot.com
https://www.apress.com/index.php/author/author/view/id/1866
On Thu, Aug 13, 2015 at 2:27 AM, arjan tijms <arjan.tijms_at_gmail.com> wrote:
> Hi,
>
> On Thu, Aug 13, 2015 at 12:34 AM, Edward Burns <edward.burns_at_oracle.com>
> wrote:
> > Spec> FlowScoped is a CDI scope that causes the runtime to consider
> > Spec> classes with this annotation to be in the scope of the specified
> > Spec> Flow. [...] beans with this annotation are created when
> > Spec> the user enters into the specified Flow, and de-allocated when the
> > Spec> user exits the specified Flow.
> >
> > But I don't think it's 100% eager. I think they only get created when
> > something such as EL tries to access it.
>
> If they only get created upon access, then isn't it the same as with
> every scope that doesn't require an ID?
>
> E.g.
>
> @Named
> @RequestScoped
> public class Foo {}
>
> ...
>
> somePage.xhtml:
>
> #{foo.toString()} <---- gets created at this point
>
> It's not necessary here to use @RequestScoped("somePage").
>
> And now it's seemingly the same with @FlowScoped:
>
> @Named
> @FlowScoped("bar")
> public class Foo {}
>
> ...
>
> somePage.xhtml:
>
> #{foo.toString()} <---- gets created at this point
>
>
> At this point the id "bar" is not used at all, since it's the name of
> the bean "foo" and the EL reference to it that caused the bean to be
> created on demand.
>
>
> With an id you could theoretically do the following:
>
> Suppose a flow with view bar.xhtml and next.xhtml both in the flow.
>
> @Named
> @FlowScoped("bar")
> public class Foo {}
>
> ...
>
> bar.xhtml
>
> (bean "foo" is created when the user enters flow "bar", since the
> system can look up the bean by its flow id)
>
> somePage.xhtml:
>
> #{foo.toString()} <---- already exists at this point
>
>
>
> > Finally, the main reason the value is necessary is that how else can a
> > FlowScoped bean be declared to be in a scope?
>
> I think just by using @FlowScoped:
>
> @Named
> @FlowScoped
> public class Foo {}
>
> With that the bean "foo" is scoped to whatever the current active flow
> is. Technically this is already what happens.
>
> The current implementation code doesn't actually use the flow id on
> @FlowScoped, except for a validation that the current flow id matches
> with the id (value) of the @FlowScoped annotation. But this is only a
> check. If you remove the check and recompile the code everything still
> seems to work. Which leads to the question, why is the check there in
> the first place?
>
> #{flowScope} is a Map<Object, Object> that's effectively flow scoped
> too, but this one does not define a flow id. It simply resolves to the
> "current" flow.
>
> Now as a consequence there is a small problem when you want to make a
> dynamic producer (Bean<T>) for #{flowScope}. You need to set the scope
> of this to @FlowScoped (no value possible here, and even if possible
> not wanted):
>
> public class FlowMapProducer extends CdiProducer<Map<Object, Object>> {
>
> public FlowMapProducer() {
> super.name("flowScope")
> .scope(FlowScoped.class) // <------- problematic with
> current implementation
> .qualifiers(new FlowMapAnnotationLiteral())
> .types(
> new ParameterizedTypeImpl(Map.class, new
> Type[]{Object.class, Object.class}),
> Map.class,
> Object.class)
> .beanClass(Map.class)
> .create(e ->
>
> FacesContext.getCurrentInstance().getApplication().getFlowHandler().getCurrentFlowScope());
> }
>
> }
>
> In this case the Map needs to be retrieved from the *current* flow
> scope, and so for this definition it makes no sense to put a value
> that represents a specific flow id somewhere.
>
> This case too works when I remove the check for the matching flow IDs.
> (there's an alternative solution as well, but that too boils down to
> simply not doing the check).
>
> Kind regards,
> Arjan Tijms
>
>
>
>
>
>
> >
> > Ed
> >
> > --
> > | edward.burns_at_oracle.com | office: +1 407 458 0017
> > | 59 Business days til JavaOne 2015
> > | 74 Business days til DOAG 2015
>