Classloader isolation and jar manifest Class-Path headers

Question

I have a system where I am loading a set of jars, each with its own URL classloader. So, Jar a is loaded by Loader A, jar b is loaded by Loader B, and so on.
Each jar has a Manifest Class-Path entry declaring its dependence on other jars. So in the example above, a puts c.jar in its Class-path, and, let's say, b also puts c.jar in its Class-path, unbeknownst to a.
Let's say there's a class Foo in c.jar. I want--need--it to be the case that (loader of a.jar == Foo.class.getClassLoader()) from the perspective of classes found in a.jar, and (loader of b.jar == Foo.class.getClassLoader()) from the perspective of classes found in b.jar.
That is, I want a and b to have their own isolated "copies" of c.jar.
Instead, what I'm finding is that Foo.class is loaded once, and his loader "leaks" over to the other jar's loader, if that makes any sense.
Is there any way to accomplish what I am talking about here?
Laird

Answer 1

As I understand the question - no.Hi; I think you misunderstand the question.
The classes are being loaded by the system loader.
Thus there is no way to seperate them.
If you want them seperate then you must use an
explicit class loader to load them.I am using explicit loaders to load them. Let me try again, because I don't think I was clear.
I have an application that has, let's say, nothing at all in its classpath. That is, it was invoked via "java ApplicationMainClass". No classpath.
Now that application reads, let's say, a properties file containing a list of URLs that point to jars.
Now the application creates a new URLClassLoader for each such URL. So if the mythical properties file has ten lines, then I create ten classloaders, each of which points to one and only one URL.
My problem is, even classes loaded by these isolated, separate classloaders are "leaking" across to other loaders. Remember, the parent classloader of all of these classloaders can't see the jars. Its classpath was empty, remember?
The issue is that the findLoadedClass() method of java.lang.ClassLoader scans the whole VM to see if a given Class was loaded before, and if it was, then by default that Class is simply returned. But I don't want that behavior.
Now, I also don't want the behavior of having to load the silly things off disk each and every time. So how do I retain this true multiple classloader isolation?
Thanks,
Laird