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From Jeremy Boynes <jboy...@apache.org>
Subject Re: [taglibs] XPath support
Date Sun, 11 Jul 2010 05:38:48 GMT
I've added two attachments to bug 27717
    https://issues.apache.org/bugzilla/show_bug.cgi?id=27717
that show ExprSupport updated to use the JAXP XPath API to precompile expressions and an implementation
of an XPathVariableResolver that handles the JSTL variable resolution scheme.

There are very few tests for the XML tags so I want to add more to check for regressions and
that may take a while. Comments on the approach would be appreciated before I start on the
other tags. I'll post some performance numbers once I've updated <x:forEach>

Cheers
Jeremy

On Jul 9, 2010, at 9:56 PM, Henri Yandell wrote:

> On Fri, Jul 9, 2010 at 12:51 PM, Jeremy Boynes <jboynes@apache.org> wrote:
>> In light of the performance issues logged against the XML taglib and functional issues
like #49578, I was looking at refactor the XML tags to use the JAXP XPath API to pre-compile
expressions and dynamically resolve variables. I think this can be done fairly easily and
will eliminate a lot of the integration code in XPathUtil. However, I could not see how to
expose the full iteration context described in the spec for <x:forEach>:
>> 
>> * the context position is the iteration 'count' (with the same meaning as in <c:forEach>)
>> * the context size is equal to the number of nodes in the node-set over which <x:forEach>
is iterating
>> 
>> It looks like the current implementation does not support this:
>>        https://issues.apache.org/bugzilla/show_bug.cgi?id=22765
>> and in testing these functions always return -1 and 0 respectively.
>> 
>> Presumably these should be returned by the XPath core functions position() and last()
respectively. However, the JAXP API only allows a single Node to be passed in for evaluation
and I could not see a way to provide the context needed by these functions. I think this might
be a limitation of JAXP.
>> 
>> I plan to go ahead with the refactor as I think by simplifying our implementation
we will address the current performance issues and fix some of the functional edge cases.
It will also remove the hard dependency on the Xalan implementation.The iteration context
functions will remain broken consistent with the current implementation.
>> 
>> It might be possible to make this work using the low-level internal Xalan APIs as
this functionality is supported in Xalan's XSLT processing. To support this in the future,
I'll try to make the XPath usage pluggable so we can drop in a Xalan-specific version in the
future.
>> 
>> Thoughts?
> 
> +1. Resolving the speed and some of the issues is worth making it
> harder to resolve the other issues imo.
> 
> Hen
> 
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