Embedded Tomcat 4.0.3
Took some time to figure it out, but now it's ok.
I used the xerces parser in my project, and had problems with hot redeployment. When I first start JBoss, everything is ok, but when I redeploy the app, jsp loader throws exception in the load() method saying it cannot find org.w3c.dom.events.EventTarget class. But it IS there in the jars.
After playing with jars I came up with a solution. In order for everything to be clearly redeployed I had to:
1. Delete ALL parser jars from the JBoss's lib dir. I mean ALL (sax/dom, xalan, xerces, etc.).
2. Download the Java XML summer pack from: http://java.sun.com/xml/downloads/javaxmlpack.html
3. Copy those files to the lib dir
The problem is many parser jars in JBoss dist have duplicate classes, and this confuses the class loader. And sun xml pack contains all of them clearly separated to jars
Hope this info helps.