I have a case where I need to create a lot of class loaders in my application to temporarily make some code visible while user supplied scripts are running. I'm using an URLClassLoader for this and it works pretty well.
When the script terminates, I want to "unload" or "close" the class loader to free the resources.
Is it enough to set the reference to the class loader to null? I'm especially wondering if I'll eventually run out of file handles because the extra classes are in JAR files.
PS: Must work with Java 5 and up. Yeah, I know...
When all classes that the class loader loaded no longer have any references, and all references to the class loader itself have been erased, the class loader and the classes it loaded will be garbage collected as a group.
Note that this is dependent on having the JVM attribute set that causes unreferenced classes to be unloaded. It's set by default in most environments, but may not be in some embedded cases.
[Note that it's a non-trivial matter to remove references to a class. Any other class that references it by name will of course prevent removal. So the class must be loaded using ClassLoader.findClass or something similar.]