I put some utilizable jar file under WEB-INF/lib. But error shows Jboss3 can't find the jar. I have to put it under jboss/server/default/lib.
And my /WEB-INF/classes contains some normal class file which are not servlet. Error report to me : JBoss3 can't find the specific class. But servlets(I added mapping in web.xml) can be loaded and works well.