Re: xalan usage in taglibs

--Apple-Mail=_1EAC06DB-9BB1-499B-9FC6-36160DA31B7A
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=utf-8

On Nov 26, 2017, at 6:32 AM, Matthew Broadhead =
<[email protected]> wrote:
>=20
> Hi,
> I am currently evaluating whether the Xalan dependency can be dropped =
from taglibs and replaced with javax.xml.*.
>=20
> 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:3=
97)
>     at =
org.apache.xalan.templates.StylesheetRoot.newTransformer(StylesheetRoot.ja=
va:200)
>=20
> In org.apache.taglibs.standard.tag.common.xml it seems like =
org.apache.xpath.XPath could be replaced with =
javax.xml.xpath.XPathExpression.
>=20
> 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.
>=20
> Can anyone shed some light on the inner workings of this function?

This was added =
<https://svn.apache.org/viewvc?view=3Drevision&revision=3D1054175> in =
1.2.x to fix a performance problem (bug #27717 =
<https://bz.apache.org/bugzilla/show_bug.cgi?id=3D27717>) 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=3D=
markup&pathrev=3D1054175#l126> still in the test class if you want to =
see if that=E2=80=99s 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=E2=80=99s the low-level equivalent of a custom =
XPathVariableResolver.

If you=E2=80=99re not using the XML tags, you may be able to simply drop =
the Xalan dependency from your application to avoid the conflict.=

--Apple-Mail=_1EAC06DB-9BB1-499B-9FC6-36160DA31B7A--