Java Dynamic classloader throws ClassNotFoundException

Question

I have a project that has it's own classloader. But I'm having a strange problem when loading some classes.

Basically, it is like:

@Override
protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException
{
    // do some magic
    return myBrandNewClas;
}

But what happens is that, even returning a class, the Class.forName(...) still throws a ClassNotFoundException (example can be found here).

Another info: the returned class' name is different of the requested class name.

I'm start wondering whether it is a security lock of JVM (tested in Oracle JVM).

Thanks!

JP Moresmau · Accepted Answer · 2015-04-17 12:40:47Z

3

The code for forName is native so it's harder to see, but yes I'd say the name is checked, because passing the correct name works:

public class BBB
{
public static class a {

}

private static class MyCL extends ClassLoader
{
    @Override
    protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException
    {
        System.out.println("Hi, " + a.class.getName());
        return a.class;
    }
}

public static void main(String[] args) throws ClassNotFoundException
{
    MyCL cl = new MyCL();

    System.out.println(Class.forName("com.asg.util.BBB$a", true, cl));

}

answered Apr 17, 2015 at 12:40

JP Moresmau

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2 Comments

Dawnkeeper Over a year ago

Also see here

Berne Over a year ago

Thanks, guys. I guess I will have to change something in my architecture :(

Berne · Accepted Answer · 2015-04-17 14:11:50Z

I could solve the problem by renaming the class to the desired class name.

import javassist.ClassPool;
import javassist.CtClass;


public class AAA
{
    public static class B
    {
        @Override
        public String toString()
        {
            return "B";
        }
    }

    private static class X extends ClassLoader
    {
        @Override
        protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException
        {
            try
            {
                if ("A".equals(name))
                {
                    ClassPool cp = ClassPool.getDefault();
                    CtClass clazz = cp.get("AAA$B");

                    clazz.setName("A");
                    return clazz.toClass();
                }

                return super.loadClass(name, resolve);
            }
            catch (Exception e)
            {
                throw new RuntimeException(e);
            }
        }
    }

    public static void main(String[] args) throws Exception
    {
        X x = new X();
        System.out.println(Class.forName("A", true, x).newInstance().toString());
    }
}

This works well, so far. Now I'll put this code in my project.

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