So to run the tests I could reverse the changes of the commit and then
update to javax.xml.* and run tests?
I am still struggling a bit to understand exactly what is happening wrt
VariableStack and how I can change over to XPathVariableResolver. And
also don't see a way to replace XBoolean, XNumber, XString etc...
I will keep trying things. Can I come back to you with specific queries?
On 26/11/2017 17:33, Jeremy Boynes wrote:
On Nov 26, 2017, at 6:32 AM, Matthew Broadhead <matthew.broadh...@nbmlaw.co.uk>
wrote:
Hi,
I am currently evaluating whether the Xalan dependency can be dropped from
taglibs and replaced with javax.xml.*.
The reason for this is a conflict which occurs when I have Apache Fop as a
dependency:
java.lang.ClassCastException: org.apache.xml.dtm.ref.DTMManagerDefault cannot
be cast to org.apache.xml.dtm.DTMManager
at org.apache.xml.dtm.DTMManager.newInstance(DTMManager.java:137)
at org.apache.xpath.XPathContext.<init>(XPathContext.java:102)
at org.apache.xpath.XPathContext.<init>(XPathContext.java:349)
at org.apache.xpath.XPathContext.<init>(XPathContext.java:337)
at
org.apache.xalan.transformer.TransformerImpl.<init>(TransformerImpl.java:397)
at
org.apache.xalan.templates.StylesheetRoot.newTransformer(StylesheetRoot.java:200)
In org.apache.taglibs.standard.tag.common.xml it seems like
org.apache.xpath.XPath could be replaced with javax.xml.xpath.XPathExpression.
But the thing I don't understand is the method getContext in
org.apache.taglibs.standard.tag.common.xml.XalanUtil uses a VariableStack and
returns an XPathContext. I am not sure how they fit into the SAX (?) model.
Can anyone shed some light on the inner workings of this function?
This was added <https://svn.apache.org/viewvc?view=revision&revision=1054175> in 1.2.x to fix a
performance problem (bug #27717 <https://bz.apache.org/bugzilla/show_bug.cgi?id=27717>) with
x:forEach. At the time, the default XPath implementation in javax.xml had the same n^2 behaviour as the
previous implementation. There are some micro-benchmarks
<https://svn.apache.org/viewvc/tomcat/taglibs/standard/trunk/impl/src/test/java/org/apache/taglibs/standard/tag/common/xml/ForEachTagTest.java?view=markup&pathrev=1054175#l126>
still in the test class if you want to see if that’s still true.
Memory is a little fuzzy, but IIRC the JSTLVariableStack is used to make the
JSP implicit variables (e.g. ${request.something}) resolvable in the transform.
It’s the low-level equivalent of a custom XPathVariableResolver.
If you’re not using the XML tags, you may be able to simply drop the Xalan
dependency from your application to avoid the conflict.
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