Interesting - sounds like its modeled after Group of 4, Decorator Pattern...
These event listeners - are they passive or do they muck with the result
stream?
-jeff
----- Original Message -----
From: "Christian Cryder" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, June 06, 2001 11:37 AM
Subject: RE: Work flow RFC
> > The lead on the Barracuda project is a subscriber to the Struts list!
> > Christian Cryder ([EMAIL PROTECTED]). He was the one who said he
> > likes to "lurk" and spoke about security
>
> Yes, I lurk. Too much to on my plate to be more actively involved ;-)
>
> As didge pointed out:
>
> > From Barracuda's Scope Summary (see,
> > http://barracuda.enhydra.org/Barracuda/docs/scope_summary.html#2.4),
> > Barracuda's scope explicitly excludes application flow control.
>
> This is correct. Barracuda does not force any particular workflow on a
> system. That said, it was designed from the get-go so as not to preclude
it
> either...I know we've already had at least one person build an XML driven
> workflow engine on top of Barracuda (I don't think it was public though).
>
> Basically, what Barracuda gives you is this:
>
> 1. Event model - converts HTTP Requests into true, first class event
> objects, which can then be dispatched to all interested listeners.
> Additional events can be fired, etc.
>
> 2. Component model - a suite of strongly typed, Swing-like MVC components
> that can be used to manipulate DOM objects, instead of using the DOM apis.
>
> 3. Form mapping & Validation framework - Automatically convert HTTP Req
> params to first class objects and apply any number of validation rules to
> them.
>
> 4. Localization services - automatically localize *ML templates (based on
> property files) and create XMLC objects from them; ability to load the
> proper template based on a Locale (much like ResourceBundles, it finds the
> closest match)
>
> Each of these sub-systems are self contained and can be used independently
> from one another. In the case of work flow, its the event model portion
that
> would prove particularly useful. Here's how it could be applied (I think
> this is described in the Barracuda docs somewhere but I couldn't locate it
> this morning, so here's a brief summary)
>
> In Barracuda, there are two types of events: ControlEvents and ViewEvents
> (which nicely map to the Http Req/Resp paradigm). When the user does
> something on the client that results in an HttpRequest, that request will
> get translated to a ControlEvent, which then gets delivered to listeners.
> However, there's more to the event dispatch process than might first meet
> the eye.
>
> Control events implement a nifty little interface called Polymorphic. This
> tells the dispatcher "hey, before you dispatch me, dispatch all my parent
> events too (since I am after all an _instance_ of those events as well").
So
> if the event hierarchy looks something like this:
>
> AuthorizedEvent
> HREvent
> FireEmployee
> HireEmployee
>
> If the client generates a HireEmployee event, this system will first fire
an
> AuthorizedEvent, then an HREvent, then the actual HireEmployee event. This
> allows me to install a listener on AuthorizedEvent or HREvent to first
> _validate_ that the client actually has the necessary authority to invoke
> the event they're trying to fire. If they don't, I can wipe the event
queue
> and completely redirect the application flow simply by firing a different
> event. For instance, if they're not already logged in, I could fire a
> GetLoginEvent to redirect them to the login screen.
>
> This process can be applied to workflow quite easily. Basically all you
have
> to do to define a workflow system is create a mechanism for indicating
which
> events can be fired for a given user state. This could take a number of
> different forms: you might have a mechanism that controls event firing
based
> on user roles, or a statechart engine, or an XML schema approach...there
are
> a tons of different options (which btw, is why we didn't just build a
> workflow engine directly into Barracuda...there are two many ways of doing
> workflow, so we didn't want to lock anyone into one particular approach).
>
> At any rate, hopefully this better explains how "No, Barracuda does not
> provide a workflow engine but Yes, its event model mechanism is very well
> suited to that problem domain".
>
> The other question is "Could Barracuda be used to glue a workflow engine
> into Struts". I think the answer is yes, but I'm not a Struts guru so I
> won't try and offer any details. Basically, the Barracuda event model
> provides Model 2 flow control...your event handlers would have to be done
> with Barracuda style code, but I don't see any reason why your view event
> handlers couldn't just redirect to the appropriate JSP page.
>
> Ok, I'll shut up now ;-)
>
> Christian
> (See why I just lurk? Its too time consuming when I get involved in
> discussions! ;-)
> ------------------------------------------------
> Christian Cryder [[EMAIL PROTECTED]]
> Barracuda - MVC Component Framework for Webapps
> http://barracuda.enhydra.org
> ------------------------------------------------
> "What a great time to be a Geek"
>
>
> > -----Original Message-----
> > From: Jonathan [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, June 05, 2001 11:10 AM
> > To: [EMAIL PROTECTED]
> > Subject: Re: Work flow RFC
> >
> >
> > The lead on the Barracuda project is a subscriber to the Struts list!
> > Christian Cryder ([EMAIL PROTECTED])
> > He was the one who said he likes to "lurk" and spoke about security on
> > Monday May 7, "RE: Potential Security Flaw in Struts MVC"
> >
> >
> > ----- Original Message -----
> > From: "Ted Husted" <[EMAIL PROTECTED]>
> > To: <[EMAIL PROTECTED]>
> > Sent: Tuesday, June 05, 2001 12:48 PM
> > Subject: Re: Work flow RFC
> >
> >
> > > I'm still fuzzy on the mechanism we would use to represent and enforce
> > > the workflow. There has been mention of things like command tokens,
but
> > > are any code samples available.
> > >
> > > Can anyone explain how Barracuda implements their workflow, and
whether
> > > it could be mapped to the Struts Actions/ActionMappings model?
> > >
> > > I believe Barracuda and Struts are complementary in most ways, and it
> > > would be in our best interest to adopt and adapt rather than
> > > roll-our-own, if feasible.
> > >
> > > Jonathan wrote:
> > > >
> > > > Again, Ive got to say look at the Barracuda project. They have one
of
> > these
> > > > gui configurers. Check it out at
> > > > http://barracuda.enhydra.org/Barracuda/GetBConfig.event
> > >
> >
>
>
