> On Nov 27, 2017, at 7:38 AM, Romain Manni-Bucau <rmannibu...@apache.org> 
> wrote:
> 2017-11-27 16:31 GMT+01:00 Jeremy Boynes <jboy...@apache.org>:
>> On Nov 27, 2017, at 12:07 AM, Matthew Broadhead
>> <matthew.broadh...@nbmlaw.co.uk> wrote:
>> In TomEE 7.0.3 everything is fine at startup.  But if a webapp is reloaded I
>> get
>> java.lang.ClassCastException: org.apache.xml.dtm.ref.DTMManagerDefault
>> cannot be cast to org.apache.xml.dtm.DTMManager
>> and the whole container needs to be restarted which is not ideal during
>> production
>> Now in TomEE 7.0.4 I cannot even start without this error so I cannot
>> upgrade.
>> It seems like a classloader issue but taglibs is the only hardcoded
>> dependency on xalan
>> Are you including the taglibs jars in your war when deploying to TomEE? You
>> shouldn’t need to do that as TomEE should be providing its own
>> implementation of JSTL which would mean there is a chance of conflict if you
>> also include them.
> Issue is xalan conflicts very easily in terms of transitive deps.
>> From a thread on tomee-users, it sounds like TomEE could be trying include
>> taglibs and avoid including the Xalan dependency but I wouldn’t expect that
>> to work as it actually is needed by the XML tags. The dependency is
>> “provided” scope to avoid automatic transitive inclusion for applications
>> that don’t use the XML tags (which is most). For container integration it
>> should be included as an application might use those tags.
> TomEE bundles taglib and therefore must bundle xalan otherwise several
> features don't work and TCK don't pass.

That was one of the tradeoffs in fixing #27717. I tried to use pure JAXP and 
the implementation from the JRE but it had the same issue as the way 1.1 
worked, perhaps not surprisingly given they are both Xalan based. To avoid 
rebuilding the DTM for each XPath execution, the tags work the same way an XSLT 
does, creating the DTM once and then evaluating the expression using the DTM. 
Unfortunately that meant using the low-level Xalan DTM APIs hence the direct 
dependency. The trade off doing this was:

a) do nothing, leaving #27717 unresolved
b) use Xalan as a dependency that was only actually needed if the XML tags were 
used in an application
c) shade Xalan and increase the library size when most users wouldn’t need it
d) refactor the XML tags into a separate taglib from the others so users would 
need to include multiple libraries

Option b) seemed like a reasonable compromise because:
- users on a Servlet-profile container would not have JSTL provided by the 
container and so would control which dependencies they needed
- users on a Web- or Full-profile container would have the entire JSTL 
implementation provided by the container and the container vendor would have 
ensured the dependencies were resolved appropriately

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