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From "Sean Schofield" <>
Subject Re: [dialog] Progress on weekend experiments
Date Thu, 31 Aug 2006 19:25:41 GMT
On 8/28/06, Craig McClanahan <> wrote:
> I've checked in some progress on my experiments with how we can improve the
> Dialog functionality.  Even though they're not done yet, they are far enough
> along to want some feedback and to make them available for experimentation
> and further development.  This mail will serve as a record of my thinking so
> far, so you can get a feel for why I took the approach I've taken so far.

Great.  I think we should do more of this sandbox in progress type
stuff.  Its easier to contribute your own ideas if the other person
hasn't nailed everything down yet.

> Initially, I wanted to address two shortcomings and one expanded feature in
> our current approach:
> * Make it possible for a single user to have multiple active dialog
> instances
>   (although limited to one per JSF view, per our discussion).

Great.  I see this also handles the "aborted" dialog case (user closes
popup window.)  Nicely done.

> * Make it possible to programmatically start up a dialog instance, as well
> as
>   start one with a prefix on a logical outcome.

This will be real nice.  I see how the create method establishes a
context but will this work in a popup scenario?  User clicks on a
"Start dialog" link and the dialog starts in a new popup window.  I'm
thinking one could use a view controller for your pop up window and
call the necessary create method.  Does the programmer need to find
the first page of the dialog on their own in this instance?

> * Make it possible to plug in different state machine implementations
>   (i.e. Commons SCXML), perhaps with different detailed feature sets.

I nice to have bonus.

> I have *not* tried to address synchronizing state when the user presses the
> browser navigation buttons yet.  One can of worms at a time :-).  Rahul had
> some comments earlier today on how SWF deals with this.  Seam does something
> similar, and we'll undoubtedly need to add functionality here later.

Don't worry.  We're not going to solve this anytime soon.

> To address these initial concerns, I focused first on abstracting out the
> APIs that an application *using* the dialog feature should have to interact
> with, and then providing generic integration for the navigation handler that
> can start a new dialog, or operate an existing one.  The guts of actually
> processing the transitions, then, is delegated to a state-machine-specific
> implementation.  The key APIs are (so far) incredibly simple -- they are in
> the "shale-dialog2" module in the sandbox.  There are two fundamental
> interfaces:
> org.apache.shale.dialog2.Context:
> * Represents the current state of an active dialog instance (similar to
> Status in the current implementation)
> * One instance per active dialog, rather than one per user
> * Cached in a o.a.s.dialog2.Contexts object stored in session scope (see
> below)
>   in between requests
> * Generic phase listener (o.a.s.dialog2.faces.Dialog2PhaseListener) is
> responsible
>   for saving and restoring access to the right instance:
>   - Before render response, caches the identifier of the currently ative
> instance
>     (if any) in the JSF component tree, as a generic attribute of the view
> root.
>   - After restore view, pulls the dialog identifier out, grabs the cached
> Context
>     instance from the session scope Contexts object, and exposes it as a
> request
>     scope attribute under a well known key ("dialog2" for the moment).
> * As we did in the original impl, Context exposes a "data" property for the
> app to
>   store whatever it wants.  So, binding expressions work very similarly to
> what they
>   did before ("#{}"), but with the bugfix that it is one
> instance per view
>   instead of one instance per user.
> * Contains an advance() method that can be called to have the state machine
> work its
>   way through the transitions until it runs into a state that needs input
> from the user (in
>   the terminology of the existing impl, that means when you hit a view
> state).  The advance
>   method returns the view id of the page to display, and a generic
> navigation handler
>   implementation (o.a.s.dialog2.faces.Dialog2NavigationHandler) then does
> the actual
>   JSF navigation.  NOTE - this navigation handler is generally the only code
> that should
>   call this method.

Context stuff looks good.  I'm going to try creating a few dialogs
later tonight to actually test it out.  Maybe even add some test

> org.apache.shale.dialog2.Contexts:

The name confuses me.  I would prefer to call it ContextManager or
something like that.  IMO its too confusing (visually) to have Context
and Contexts.  They are too similar looking and I find myself stopping
and saying "Now which one is it again?"

> * Defined by a particular implementation as a session scoped managed bean
> that is
>   stored under a well known key.
> * Maintains a cache of Context instances for the current user, keyed by
> dialog identifiers,
>   so we get the one-per-view capability.
> * Includes a create() method so that you can programmatically start a dialog
> instance.

The functionality of this class looks good.  Just don't like the name.
 Is it just me or does the code look a lot cleaner with this
refactoring?  It seems easier to follow this way.

> The remaining classes in shale-dialog2 implement the JSF integration
> (navigation handler and phase listener), and should not be utilized directly
> by applications.

Makes sense.

> To validate this design, I've refactored the current support into a module
> (shale-dialog2-legacy) that does pretty much the same thing as the existing
> implementation, but organzied with the new APIs.  (Side note ... Sean is
> definitely not going to like what I did to the config classes, making
> everything I could package private ... that's my new habit when designing
> APIs ... we can make things more public later as needed, but cannot really
> go the other way.)  As I mentioned in the commit comments, this stuff has
> only been desk checked and not actually used yet, so it undoubtedly has
> bugs, but it should be easy to make functional -- and it benefits from the
> "dialog instance per view" fix in the underlying architecture to fix that
> problem.

I fixed a DTD issue in your faces-config.xml that my IDE was
complaining about.  I will put it to an actual test later today.
Don't worry about the private vs. public business.  If we take care of
the major problems there will be no need to subclass anymore.

> A corresponding module for Commons SCXML has been started, but I got
> sidetracked a bit on the legacy one.  It'll be pretty easy to finish this
> off in a similar fashion, though ... that'll be my next step unless someone
> wants to volunteer to beat me to it.

I see Rahul has volunteered for this.  Better him then me ;-)  I think
we should ship 1.0.4 with the "legacy" implementation and ship SCXML
when its ready.  Also, I think we should change everything from dialog
to dialog2, etc. once we move out of the sandbox.  I'm assuming this
"2" and "legacy" stuff is just to keep us from getting confused until

Nice work.

> Craig


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