Hi,
DocumentFactory (or some class that DocumentFactory calls) uses an org.xml.sax.InputSource. This class is also defined both in rt.jar from
the JDK distribution as well as in weblogic.jar. When DocumentFactory tries
to load InputSource, AntClassLoader looks at "org.xml.sax.InputSource" and says "that's not a system package", and thus it (AntClassLoader) loads the
class using it's own rule(s) (which really just use the classpath I have
defined in my build.xml).
Just to note a little point. The DocumentFactory is not creating the InputSource instance. It it were it would have used the SystemLoader (Its classloader) and the AntClassLoader would not have got a chance to create the class.
When all the dust settles, I have a DocumentFactory from the JDK and an InputSource from weblogic. The two don't line up, and I get a LinkageError.
Actually you probably have two InputSource classes, one from weblogic and one from the JDK. Since the DocumentFactory instance sees both these classes, this is the LinkageError.
I changed the source code for the constructor for AntClassLoader so that it
does *not* add javax as a system package. This forced AntClassLoader to
load the DocumentFactory from weblogic.jar instead of rt.jar, and since InputSource is read from weblogic.jar everything lined up and the my unit
test ran successfully.
You must be very careful with this :-). The javax package is problematic because it is common in both the JDK (system loader) and in app servers but with different sets of available classes. What you have done may work but it may be just waiting to break. I have had situations where if I ran a test twice it would get a linkage error because the classes from the first run would not have been GC'd yet. Putting in a delay (or debugging it) and it would work.
If you are using JUnit to test code that relies on AppServer classes, it is almost always safer to set fork="yes" as Steve suggested.
Conor
