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From "Frank W. Zammetti" <>
Subject Re: Client-side Digester?
Date Thu, 08 Dec 2005 00:33:11 GMT
Just a quick update, I've actually had some time yesterday and today to 
work on this idea, and I'm happy to say I've gotten a decent amount of 
work done.

At present I have JSDigester (as I've taken to calling it) with three 
rules implemented (ObjectCreate, SetProperties and BeanPropertySetter). 
  I need to complete one or two more rules to complete my first-pass 
test harness, which is an object graph representing a movie collection.

Once I get that done, as soon as tomorrow I'm hoping, I was thinking of 
posting it for folks to have a look at and see if anyone thinks its 
worth continuing on.  I know I'm going to be using it either way in an 
upcoming project, but frankly once its at the point I need it to be at, 
my only incentive to take it further would be if there was any interest 
in possibly bringing it into Commons in some fashion, so I'm fishing to 
see if there is any interest in that :)

Incidentally, I also threw together what looks a bit like a Javascript 
implementation of JCL for this :)


Frank W. Zammetti wrote:
> Martin Cooper wrote:
>> On 11/26/05, *Frank W. Zammetti* < 
>> <>> wrote:
>>     Craig McClanahan wrote:
>>      > If you're using JavaScript, why would you restrict yourself to 
>> that
>>      > (even if you *could* figure it out)?  You can dynamically
>>     add  fields to
>>      > a JavaScript object, so an analog of the set properties rule
>>     would just
>>      > define a field on the object for every attribute in the XML 
>> element.
>>     That's a good point... that thinking leads to a path where instead of
>>     populating pre-made objects from a parsed XML document, the objects
>>     themselves are created on-the-fly.  Or more precisely, you 
>> wouldn't have
>>     to deal in pre-defefined objects.
>> At that point, you've just reduced the problem to parsing XML in 
>> JavaScript, which is a solved problem. ;-)
> Haha, in a way, yeah :)
> It's more the event-oriented model of Digester though that I don't think 
> there's an analogy for yet in Javascript... not without knowing 
> something about the DOM structure before-hand anyway.
>> Putting the conversion in the setter would be unfortunate, since 
>> you've then embedded knowledge in that setter that would have 
>> otherwise been confined to the Digester rules.
> I would agree if we were talking about a 1:1 conversion of Digester... 
> but as Craig previously pointed out, it's probably not possible, or even 
> desireable, to try to do a 1:1 conversion.  One could make the argument 
> with normal Digester that things would be a lot simpler if all you ever 
> had was setXXX(Object), and the object itself took care of type 
> conversions as it probably knows what it needs better than Digester 
> does... in Javascript you almost have no choice but to think of it that 
> way :)
>> Note that ObjectCreateRule is going to be, um, "interesting", for a 
>> couple of reasons. Probably the trickiest thing is going to be finding 
>> the class that you need to instantiate, since you won't have Java's 
>> class loading mechanisms to help you out. 
> Excellent point.  It might be enough to simply state that any class to 
> be instantiated by Digester has to be available in page-scope before the 
> parse() method is called, and leave it at that.  The developer will have 
> to include the correct import or include or whatever they do.  But this 
> is clearly something that needs to be thought through.
>  > You're going to need to
>> implement some kind of dynamic loading scheme, and the classes you 
>> instantiate are going to have to play by the rules you define for 
>> that. (BTW, Dojo has one you could use. ;) 
> Yep, that's one answer, and seeing what Dojo offers would be a good idea 
> in that case.
>  > Also, many uses of (Java) Digester
>> take advantage of zero-arg constructors, a la JavaBeans, but most 
>> classes in JavaScript don't have such things, so you'll need to be 
>> passing in parameters to those constructors.
> But, IIRC, that is a requirement of the spec, right?  So, if there is a 
> basic assumption that any class Digester will work with follows the 
> spec, that should take care of it.
>> Just a couple of thoughts off the top of my head.
> Yeah, it'll definitely be an interesting road :)  I probably won't try 
> and start until Monday, but I'm actually looking forward to seeing what 
> I can put together next week.
> Frank

Frank W. Zammetti
Founder and Chief Software Architect
Omnytex Technologies
AIM: fzammetti
Yahoo: fzammetti

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