The mock classloader isn't documented anywhere AFAIR, I only created it for testing purposes. The importAll and exportAll (not in the MockClassLoader) are meant to duplicate what the old UCL does. In the example you quote, it does do "importAll" so it will load from the whole domain that the classloader belongs to. The mock classloader has two important properties. setPackages() - what is exported setPaths() - what is part of the classloader (but not necessarily exported to other classloaders) There is a convience method to do both, setPackagesAndPaths() In the api you show, the "PACKAGE_A" is what is included in the classloader and what is exported. The "true" means it will "importAll", i.e. look at all other classloaders in the order they were registered to find the class before looking at its own private (non-exported) classes. Try adding enableTrace("org.jboss.classloader") to the test and you will see in detail where it is trying to load classes from and where it found it. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4076738#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...