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?
Jeremy
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