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From robert burrell donkin <>
Subject Re: Simple XML filter for Digester
Date Tue, 29 Jul 2003 17:31:31 GMT

On Tuesday, July 29, 2003, at 02:02 AM, Craig R. McClanahan wrote:

> On Mon, 28 Jul 2003, robert burrell donkin wrote:
>> Date: Mon, 28 Jul 2003 23:50:17 +0100
>> From: robert burrell donkin <>
>> Reply-To: Jakarta Commons Users List <>
>> To: Jakarta Commons Users List <>
>> Subject: Re: Simple XML filter for Digester
>> hi Aaran
>> i'm afraid that i don't know of an easy way to do this (currently). the
>> pattern matching rules don't look for attributes and anyway can't be
>> easily modified dynamically.
>> this could probably be done using a filter for the SAX events (but that
>> might be a little tough since you're new to xml). maybe some kind of
>> generic filtering could be added to digester (but i'm not sure how easy
>> this would be).
>> any one else have any good ideas about how to solve this one?
>> - robert
>> On Saturday, July 26, 2003, at 03:49 AM, Aaran Stent wrote:
>>> Hello,
>>> I am new to XML, after reading all of the hype I have fond disgester is 
>>> a
>>> actually a practicle way of using XML in a "real world environment".  I
>>> have
>>> setup a digester object to load select/combo boxes for my 
>>> application.  A
>>> simple XML example follows:
>>> <combos>
>>> 	<combo name="colour">
>>> 		<option id="1" value="blue">
>>> 		<option id="2" value="black">
>>> 		<option id="3" value="red">
>>> 	</combo>
>>> 	<combo name="streets">
>>> 		<option id="1" value="street">
>>> 		<option id="2" value="court">
>>> 		<option id="3" value="road">
>>> 	</combo>
>>> </combos>
>>> This works fine, i can load all of the objects into a LinkedHashMap but 
>>> I
>>> want to reuse the combo boxes witout having to clone objects.  I would
>>> like
>>> to tell the digester to load just one object based on an attribute in a
>>> tag.
>>> eg MyComboBoxClass colour = loadCombo("colour");
> Why can't you just call:
>   MyComboBoxClass colour = (MyColour) linkedHashMap.get("colour");
> It seems like a lot of extra effort to reparse the XML every single time.


(though i suspect that the repeated xml parsing is an alternative to 
cloning the object in the hashmap.)

i've been thinking about this and wondering whether adding filtering to 
digester might be useful. SAX filters in the pipeline above digester is 
probably the most effective way to implement this kind of functionality 
but maybe there's a niche for simple filtering in the digester layer 
before the matches are processed.

maybe one day real pipelining would be cool but a simple filter which 
would suppress processing of certain elements based on the information 
similar to that contained in the begin signature in digester would be 
quick to implement and easy to use.


- robert

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