in terms of adding support for attribute matching, i'm a little reluctant to consider modifying the matching string syntax but i suppose that we could add a wrapper rule (even though it's not a very elegant solution).
the current design for Rules makes it easy to create new rules implementations but is limited by the amount of information available to the implementation. the string syntax passed into the call is the limiting factor.
this has set me wondering whether something like XSLT would be a cool to map XML to objects. rather than templates, rules would be applied to the products of XPath expressions. xml rules could probably be mined but still would be a lot of work.
- robert
On 11 Apr 2004, at 14:31, robert burrell donkin wrote:
this may well be completely left field but...
i wonder whether it might be possible to use SAX pipelining to add XPath support. rather than changing digester, create a filter that splits the SAX feed and sends one copy to a special engine and another direct to standard digester. the special engine could then use a standard SAX-based XPath implementation.
the only problem is what is i think is (with hindsight) the major flaw with the current design: rule implementations have a dependency on digester rather than an abstract, minimal RulesEngine. so (sign) it would probably be a bit of hack to do this kind of thing with digester 1.
- robert
On 9 Apr 2004, at 21:07, Chen, Tim wrote:
Thanks Simon :)
I just recently started using Digester so I don't yet know enough about it's
innards to make a change to it but I'll definitely keep that in mind :)
-Tim
-----Original Message----- From: Simon Kitching [mailto:[EMAIL PROTECTED] Sent: Friday, April 09, 2004 4:04 AM To: Jakarta Commons Users List Subject: Re: Digester and attribute matching?
On Fri, 2004-04-09 at 04:36, Chen, Tim wrote:processingI saw that in the list archives it was not supported but 1) is it planned to be able to support something like digester.addCallMethod("[EMAIL PROTECTED]"blah"\]", "foo"); ? 2) is there a way around it currently? I see that all the rules have a way to see the attributes beforebut I don't know how to stop that rule from processing.
No, there is no support for this kind of conditional matching in Digester.
I can see that it would be nice for digester to have it, but I wouldn't
have a clue how it could be implemented (efficiently and elegantly). It
isn't planned any time in the near future, because as far as I know,
none of the current Digester developers have a need for this feature.
I've got it as a bullet-point for consideration for Digester-2.0. but
that could be quite a while away (if ever).
But that's where the power of "open source" comes in - if you want the
feature, please feel free to implement it. If you can come up with some
proof-of-concept code that shows how this could be done in Digester,
then I (and I'm sure others) would be very interested. I am happy to
(try to) answer any questions you have if you do decide to tackle this.
Note, however, that spending 5 minutes to write some pseudo-code
probably won't motivate any of the existing regular developers to then
implement it for you :-).
I got involved with Digester because I wanted an extra feature,
implemented it and submitted it as a patch. So from experience I can say
that contributions *are* welcome.
If all you want is to prevent CallMethodRule instances from firing if
certain attributes have certain values, then you *may* get away with
subclassing CallMethodRule, and storing a boolean flag on the rule
instance. Set the flag to true/false in begin(), according to the
attribute values, and then in body/end methods, just test the flag and
skip the call if the flag is set. Note that this is not a proper
general-purpose solution, as it can fail horribly if you use that
CallMethodRule with patterns containing wildcards. But if that is not
the case for your application, then you can ignore this issue.
Regards,
Simon
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