XOM API for Processing XML with Java

[Michael Abato <mrabato AT earthlink.net>]

I have verified that the problem definitely remains for tomcat (3.3.x 
thru 5.0.x) and websphere 5.1. According to 
http://nagoya.apache.org/jira/browse/XERCESJ-976 (section 2) it will be 
a problem for all servlet, J2EE, and other containers using multiple 
classloaders. The problem is that XOM does

>                 System.setProperty(
>                   
> "org.apache.xerces.xni.parser.XMLParserConfiguration",
>                   "nu.xom.xerces.XML1_0ParserConfiguration");

locally, in the webapp classloader, but the property is subsequently 
available to all classloaders (webapps/EJB's/etc.) which do not 
necessarily have access to nu.xom.xerces.XML1_0ParserConfiguration, and 
therefore throw ClassNotFoundException.

I've put up a sample project at 
http://home.earthlink.net/~mrabato/xom-test.tgz which includes two war 
files (and their associated source/build files). Both can be installed 
simply on any servlet container. On tomcat, use the manager webapp with 
the simple war file deployment form. 'xerces-runner' reads a trivial 
xml document via sax. 'xom-runner' does the same via XOM. If you run 
xerces-runner AFTER running xom-runner you will get the 
ClassNotFoundException.

I can see two classes of solutions: checking for XML 1.1 only if 
requested (e.g..: configured to do so with a system property) and 
checking by default, but not if in a known "container". The first means 
system properties or static methods, neither of which is great. The 
later will always "fail" on an as-yet-unwritten/unknown container.

I would favor looking for system property 
"javax.servlet.context.tempdir" (which implies you are in a servlet 
container) and respecting a user-set system property like 
"nu.xom.no-verify-XML1_0". Other known containers could be added as 
"signals" are identified. Does anyone know a good EJB signal?

Michael Abato

On Jun 8, 2004, at 11:45 AM, Elliotte Rusty Harold wrote:

> I have not yet resolved some of the class loader issues reported by 
> various people. I'd appreciate it if anyone who's encountered a 
> problem with XOM when used in TomCat or other multi-classloader 
> environments let me know if the problem still occurs with the latest 
> release. If it does, let me know and fixing that will be the highest 
> priority for alpha 2.