RE: [Springframework-developer] webflow: subflow behavior question

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Steven,

We should likely take this off-line, but just some suggestions for neat
things you could cover in your upcoming web flow article:

- Demonstrate a good case for 'transitional criteria' beyond that of a
signaled event within a state.  Show how the path through the flow can be
effected based on contextual information, for example, the value of an
object in request or flow scope.

- Demonstrate the use of the Multi-Action to centralize related flow action
logic in one place. 

- Examples showing the Java based flow builder as well as the Xml flow
builder.

- A flow execution listener implementation, for auditing or otherwise
annotating an executing client instance of a flow at specific points within
its lifecycle.

- Tips and gotchas related to browser navigation button use.

Sounds like you've got some most of the other key features covered, like sub
flows, for example.

Keith

-----Original Message-----
From: spr...@li...
[mailto:spr...@li...] On Behalf Of
Steven Devijver
Sent: Tuesday, March 29, 2005 10:31 AM
To: spr...@li...
Subject: Re: [Springframework-developer] webflow: subflow behavior question

Keith,

> 
> That's possible now, right?
That's right.

> 
> The way I see it, just have your FlowAttributeMapper implementation
> implement BeanFactoryAware to get a callback to the factory for dependency
> lookup.  Your implementation is likely already managed by Spring anyway,
so
> nothing special there.
> 
> Method injection would work here as well.

An alternative approach would be to put an action-state in front of
the flow-state that creates algorithm class instances and puts them in
the flow context. Separating mapping and state management is probably
a better approach.

> 
> I don't see the need for one-shot mappers, and quite like how the current
> implementation optimally wires the system in "for use" after
configuration.
> If we needed a one-shot mapper, we could have a FlowAttributeMapper that
was
> a proxy to a service lookup.
> 
> Keith
> 
> -----Original Message-----
> From: spr...@li...
> [mailto:spr...@li...] On Behalf
Of
> Steven Devijver
> Sent: Tuesday, March 29, 2005 8:20 AM
> To: spr...@li...
> Subject: Re: [Springframework-developer] webflow: subflow behavior
question
> 
> > Mmm. So you're thinking about a custom mapper that (in the
> > 'createSubFlowInputAttributes' method) takes a list of persons (ids)
from
> > the parent flow scope and instantiates an algorithm object, passing in
> those
> > ids. Once that is done it puts the algorithm object in the subflow
scope.
> As
> > far as I can see the mapper would still be thread safe right --
everything
> > happens in a method call with local variables?
> 
> This is indeed what I was thinking about. The mapper is the pivot
> point between two sub flows. Since the Person flow requires the
> algorithm class the mapper to me looks like the obvious point to
> create it.
> 
> Since the mapper is a singleton and I would like to use IoC to
> configure which algorithm class the mapper should use the mapper needs
> to create the algorithm instance on every call to
> 'createSubFlowInputAttributes'. This would require the use of the
> 'getBean' method of the application context and a string property on
> the mapper class to set the bean name of the algorithm class. The
> algorithm class would be stateful thus needs to be configured as a
> prototype and its instances cannot outlive the scope of a request.
> 
> >
> > All mappers (and actions) should be stateless and there should be little
> > need to make them statefull.
> 
> Agreed.
> 
> >
> > Anyway, thinking about this popped the following into my mind: currently
> the
> > flow keeps references to the mapper objects that are looked up at flow
> > configuration (build) time. The same is also true for actions and other
> > flows (i.e. for all flow services looked up via a FlowServiceLocator).
> > This is actually different from my original implementation where you
could
> > control wheter or not an action or mapper was a singleton by using the
> > "singleton" property in the application context and the mapper or action
> was
> > looked up every time it was needed. This kind of prototype mapper or
> action
> > wasn't really that usefull since you could only hold state for a very
> short
> > time: one 'use' of the object in the flow (e.g. input & output mapping
> would
> > be 2 uses, so you could not share state by making the mapper statefull).
> > However, I'm thinking that if you could have a singleton action/mapper
per
> > flow execution, you could really make the action or mapper statefull.
Not
> > sure if that would be a good idea though....just brainstorming...
> >
> > Agreed that 'porting' the old article to the new system would be a good
> > idea. When we approach Spring web flow 1.0 final I'll take care of that.
> 
> Great.
> 
> >
> > Erwin Vervaet
> > erw...@er...
> > ----- Original Message -----
> > From: "Steven Devijver" <ste...@gm...>
> > To: <spr...@li...>
> > Sent: Tuesday, March 29, 2005 8:48 AM
> > Subject: Re: [Springframework-developer] webflow: subflow behavior
> question
> >
> > > Erwin, Keith,
> > >
> > > Thanks for your feedback. Regarding thread-safety, there would indeed
> > > be no concern if the model-mapper object would be instantiated on
> > > every execution of a flow-state. Is this the case? Otherwise, the
> > > model-mapper would have no way of knowing when to create an new
> > > algorithm instance, which would contain state.
> > >
> > > Regarding the old webflow article, I find it more concise than the
> > > current docs on Confluence, it provides an excellent overview of how
> > > to get started with WebFlow and I feel it should not be discarded.
> > > With a little bit of work this article could be kept up to date.
> > >
> > > Regarding this new article, it will probably be published in the next
> > > couple of weeks. I'm discussing the creation of a wizard across
> > > multiple pages and the reuse of a subflow, the disadvantages of
> > > classic MVC for these scenarios (I'm talking based on personal
> > > experience :) and the advantages offered by WebFlow.
> > >
> > > Steven
> > >
> > > On Mon, 28 Mar 2005 12:02:41 -0500, Keith Donald
<ke...@in...>
> > > wrote:
> > >> As Erwin mentioned, there should be no concern of thread safety here.
> > >> Just
> > >> create a prototype instance that encapsulates the context you need an
> > >> pass
> > >> it to the spawned subflow.  That'll be thread safe, as operations on
> flow
> > >> executions are synchronized per session per request.
> > >>
> > >> "PersonSearchAlgorithm" will would be a callback to some kind of
> > >> contextual,
> > >> query, yes?  Yea, to me it makes sense to parameterize the sub flow
> > >> execution with an instance of an appropriate contextual
implementation
> of
> > >> that interface (e.g "all persons where manager != <x>, or all persons
> not
> > >> already attending or excluded"), delegating down to the DAO layer to
> > >> actually perform the data access.  I like the notion of this better
> than
> > >> passing in a snapshot array of persons to exclude.
> > >>
> > >> HTH! Just curious, what is the web flow article? When will it be
> > >> published?
> > >>
> > >> Keith
> > >>
> > >> Keith Donald
> > >> Interface21 - Spring Training, Consulting, and Support, "From the
> Source"
> > >> http://www.springframework.com
> > >>
> > >> -----Original Message-----
> > >> From: spr...@li...
> > >> [mailto:spr...@li...] On
> Behalf
> > >> Of
> > >> Erwin Vervaet
> > >> Sent: Monday, March 28, 2005 11:35 AM
> > >> To: spr...@li...
> > >> Subject: Re: [Springframework-developer] webflow: subflow behavior
> > >> question
> > >>
> > >> Threading issues are limited in web flows since a flow execution is
> > >> basically single threaded: i.e. the flow execution entry methods
> (start()
> > >> and signalEvent()) are synchronized. (At least this is the behaviour
in
> > >> the
> > >> new implementation in the sandbox.)
> > >>
> > >> Ofcourse you could also pass the list of ids to the Person subflow.
In
> > >> that
> > >> case your "subflow signature" would be something like
> > >>
> > >> public Person PersonFlow(String action, Person[] personsToExclude)
> > >>
> > >> We're maintaining documentation related to the "new" Spring web flow
> > >> system
> > >> at
> > >>
http://opensource.atlassian.com/confluence/spring/display/WEBFLOW/Home.
> > >> Keith Donald has been working on a new partical guide that you can
find
> > >> there.
> > >>
> > >> Regarding the "old" Ervacon Spring web flow: I will let it go to
1.0.0
> > >> and
> > >> then provide a migration guide to the new Spring web flow system.
> Ervacon
> > >> Spring web flow is still useful for those people that stick with
Spring
> > >> 1.1.x, but if you have 1.2 or later it's probably better to go with
the
> > >> new
> > >> system.
> > >>
> > >> Erwin
> > >>
> > >> Erwin Vervaet
> > >> erw...@er...
> > >> ----- Original Message -----
> > >> From: "Steven Devijver" <ste...@gm...>
> > >> To: <spr...@li...>
> > >> Sent: Monday, March 28, 2005 5:51 PM
> > >> Subject: Re: [Springframework-developer] webflow: subflow behavior
> > >> question
> > >>
> > >> > Hi Erwin,
> > >> >
> > >> > Although this is just a silly example to highlight my question
> passing
> > >> > behavior through the model does seem a bit awkward to me.
Especially,
> > >> > the behavior class would also contain state (unless the state is
> > >> > passed separately in the model but then the Person flow would need
to
> > >> > pass the state to the behavior). This would make the design not
> > >> > thread-safe.
> > >> >
> > >> > In this scenario I would prefer to pass a list of ID's of Persons
> that
> > >> > cannot be shown in the Person flow and implement the behavior once.
> > >> > I'm looking into this because I'm working on an article on webflow.
> > >> >
> > >> > btw, I found you article "Spring Web Flows: A Practical Guide" very
> > >> > helpful. Are you planning to keep it up to date with the latest
> > >> > changes to WebFlow (e.g. the changes to the action interface)?
> > >> >
> > >> > Thanks
> > >> >
> > >> > Steven
> > >> >
> > >> >
> > >> > On Mon, 28 Mar 2005 17:11:32 +0200, Erwin Vervaet
> > >> > <erw...@er...> wrote:
> > >> >> The Manager and Meeting flow indeed have to put a SearchAlgorithm
> > >> >> instance
> > >> >> in flow scope, probably in an 'initFlow' action state or something
> > >> >> like
> > >> >> that, which could also take care of any type of flow data
> > >> >> initialisation,
> > >> >> e.g. pulling in reference data.. You then use an attribute mapper
to
> > >> >> pass
> > >> >> the SearchAlgorithm to the subflow in the subflow state.
> > >> >>
> > >> >> Erwin Vervaet
> > >> >> erw...@er...
> > >> >> ----- Original Message -----
> > >> >> From: "Steven Devijver" <ste...@gm...>
> > >> >> To: <spr...@li...>
> > >> >> Sent: Monday, March 28, 2005 4:59 PM
> > >> >> Subject: Re: [Springframework-developer] webflow: subflow behavior
> > >> >> question
> > >> >>
> > >> >> > Hi Erwin,
> > >> >> >
> > >> >> >
> > >> >> >> I would probably do this by making the search (or filter)
> algorithm
> > >> >> >> configurable for the Person flow. That way the calling parent
> flow
> > >> >> >> can
> > >> >> >> pass
> > >> >> >> in the algorithm to use. I find that a good way to think about
a
> > >> >> >> flow
> > >> >> >> is
> > >> >> >> as
> > >> >> >> a method: it has input parameters and can return results. So
your
> > >> >> >> person
> > >> >> >> flow would be something like this, when expressed as a method:
> > >> >> >>
> > >> >> >> public Person PersonFlow(String action, SearchAlgorithm
> algorithm)
> > >> >> >>
> > >> >> > Does this mean the Manager and Meeting flows have to put a
> > >> >> > SearchAlgorithm instance in the session (or the model?) before
> > >> >> > passing
> > >> >> > control to the Person subflow? Does this require an action-state
> > >> >> > before the flow-state in the Manager and Meeting flows?
> > >> >> >
> > >> >> > Thanks
> > >> >> >
> > >> >> > Steven
> > >> >> >
> > >> >> >
> > >> >> > -------------------------------------------------------
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> > >> >> > _______________________________________________
> > >> >> > Springframework-developer mailing list
> > >> >> > Spr...@li...
> > >> >> >
> https://lists.sourceforge.net/lists/listinfo/springframework-developer
> > >> >> >
> > >> >> >
> > >> >>
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> > >> >>
> > >> >
> > >> >
> > >> > --
> > >> > "If you want to be a different fish, you gotta jump out of the
> school."
> > >> > -- Captain Beefheart
> > >> >
> > >> >
> > >> > -------------------------------------------------------
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> > >> >
> > >>
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> > >>
> > >
> > >
> > > --
> > > "If you want to be a different fish, you gotta jump out of the
school."
> > > -- Captain Beefheart
> > >
> > >
> > > -------------------------------------------------------
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> >
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> >
> 
> --
> "If you want to be a different fish, you gotta jump out of the school."
> -- Captain Beefheart
> 
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> 

-- 
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-- Captain Beefheart

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