Define custom system classloader

Question

I'm trying to tell the JVM to use my custom ClassLoader as default ClassLoader

This is the VM argument i use to pick my class:

-Djava.system.class.loader=JarClassLoader

and this is the error i get

Error occurred during initialization of VM
java.lang.Error: java.lang.NoSuchMethodException: JarClassLoader.<init>(java.lang.ClassLoader)
    at java.lang.ClassLoader.initSystemClassLoader(Unknown Source)
    at java.lang.ClassLoader.getSystemClassLoader(Unknown Source)
Caused by: java.lang.NoSuchMethodException: JarClassLoader.<init>(java.lang.ClassLoader)
    at java.lang.Class.getConstructor0(Unknown Source)
    at java.lang.Class.getDeclaredConstructor(Unknown Source)
    at java.lang.SystemClassLoaderAction.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.lang.ClassLoader.initSystemClassLoader(Unknown Source)
    at java.lang.ClassLoader.getSystemClassLoader(Unknown Source)

Do i have to define a specific method or am i using the wrong argument?

Answer 1

Custom ClassLoader

public class CustomClassLoader extends ClassLoader{

    public CustomClassLoader(ClassLoader classLoader) {
        super(classLoader);
    }

    @Override
    public Class<?> loadClass(String name) throws ClassNotFoundException {
        System.out.println("Loading class :" + name);
        return super.loadClass(name);
    }
}

Main Class

public class Main {

    public static void main(String[] args) {
        System.out.println("Starting main");
    }
}

VM arguments: -Djava.system.class.loader=CustomClassLoader

All classes are in default package and it executes successfully.

Output:
Loading class :Main
Starting main