Replacement System Classloader for Classes In Jars containing Jars

Question

So far, the examples I have seen for custom ClassLoaders involve subclassing the URLClassLoader, and using that specific instance to load classes in resources.

I have tried in vain to look for alternative methods to replace the SystemClassLoader, so that my ClassLoader can be consulted for classes not located in the classpath.

I tried Thread.currentThread().setContextClassLoader, but it doesn't seem to work.

Is it even possible?

Answer 1

Though this is an old question, there is indeed a way to replace the system ClassLoader. You might get more than you bargained for, however, with reflection.

        Field scl = ClassLoader.class.getDeclaredField("scl"); // Get system class loader
        scl.setAccessible(true); // Set accessible
        scl.set(null, new YourClassLoader()); // Update it to your class loader

This should work on the Oracle JVM.

Answer 2

Run JVM with java.system.class.loader property:

java -Djava.system.class.loader=myClassLoader myApplication