Attempts to call XMLInputFactory.newInstance() inside a plugin fail with this
exception:

Caused by: javax.xml.stream.FactoryConfigurationError: Provider
com.bea.xml.stream.MXParserFactory not found

I believe this is because jsr173-1.0.jar is included in the Hudson war, but no
implementation is provided. This is a transitive dependency via dom4j.

Proposed solutions (in order of my personal preference):
1) Include a StAX implementation in the Hudson war.
2) Remove jsr173-1.0.jar from the Hudson war.
3) Change the plugin classloader model so that plugin jars take precedence over
Hudson-provided jars.

Under Java 6 this is not a problem.