Please refer the scenario and the config in my first post. In the jmx-console, I invoke the getPackageClassLoaders() of the loader with the param=ClassA. It returns like that anonymous wrote : [org.jboss.mx.loading.LoadMgr3$PkgClassLoader@bb365d | {ucl=org.jboss.mx.loading.HeirarchicalLoaderRepository3$CacheClassLoader@4129e3 | { url=null ,addedOrder=0} order=1}, | | org.jboss.mx.loading.LoadMgr3$PkgClassLoader@ee37f2 | {ucl=org.jboss.mx.loading.UnifiedClassLoader3@10cf62 | { url=file:/C:/jboss-4.0.3SP1/server/default/tmp/deploy/tmp44379mdb.jar ,addedOrder=41} order=2}, | | org.jboss.mx.loading.LoadMgr3$PkgClassLoader@19b07e9 | {ucl=org.jboss.mx.loading.UnifiedClassLoader3@24fe6b | { url=null ,addedOrder=0} order=3} | ] My question is: 1. What is the meaning of "url=null"? 2. Does the "order=1", "order=2"... determine the class loading order? 3. ClassA is loaded from mdb.jar instead of the app.war. But why? FYI, I can see the package of ClassA (say com.XXX) only appears once in the ucl log. anonymous wrote : ... | [48531,UnifiedClassLoader,main] New jmx UCL with url file:/C:/jboss-4.0.3SP1/server/default/tmp/deploy/tmp44379mdb-1.3.jar | [48531,RepositoryClassLoader,main] setRepository, repository=org.jboss.mx.loading.UnifiedLoaderRepository3@1da669c, cl=org.jboss.mx.loading.UnifiedClassLoader3@10cf62{ url=file:/C:/jboss-4.0.3SP1/server/default/tmp/deploy/tmp44379mdb-1.3.jar ,addedOrder=0} | [48531,RepositoryClassLoader,main] setRepository, repository=org.jboss.mx.loading.UnifiedLoaderRepository3@1da669c, cl=org.jboss.mx.loading.UnifiedClassLoader3@10cf62{ url=file:/C:/jboss-4.0.3SP1/server/default/tmp/deploy/tmp44379mdb-1.3.jar ,addedOrder=0} | [48531,UnifiedLoaderRepository3,main] Adding org.jboss.mx.loading.UnifiedClassLoader3@10cf62{ url=file:/C:/jboss-4.0.3SP1/server/default/tmp/deploy/tmp44379mdb-1.3.jar ,addedOrder=0} | [48547,ClassLoaderUtils,main] Indexed pkg: com.XXX, UCL: org.jboss.mx.loading.UnifiedClassLoader3@10cf62{ url=file:/C:/jboss-4.0.3SP1/server/default/tmp/deploy/tmp44379mdb-1.3.jar ,addedOrder=41} | [48547,ClassLoaderUtils,main] Indexed pkg: com.XXX.YYY, UCL: org.jboss.mx.loading.UnifiedClassLoader3@10cf62{ url=file:/C:/jboss-4.0.3SP1/server/default/tmp/deploy/tmp44379mdb-1.3.jar ,addedOrder=41} | ... It's difficult to post the class loading log here as it is too large. Could you suggest what thing I should post here? Thanks. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3957959#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...