Override and extend default ClassLoader

Question

Hi,
I've been messing around with the ClassLoader for a long time now (maybe 8 hours) and i just dont get it.
What it try ist to do the following:
Store the class Test.class in a package. (somewhere) The class Test can have many versions (plugin-system).
A developer should be able to code like this without bothering which version the Test.class has.
Test t = new Test();
Now the problem comes:
I want MY ClassLoader to load the Test.class defined in a XML with the newest version. Or (maybe) an other version defined by an XML file. Again the programmer should not have to work with reflect to use the Test.class.
I've written my own ArchiveLoader class which extends the ClassLoader and used the -Djava.system.class.loader=ArchiveLoader setting. But: My ArchiveLoader.loadClass()-Method is only called to load the Main Class and i just dont get why. Any other class is loaded by the AppClassLoader.
If ANYONE could just post an complete example how to tell java to look at mine loader first.... I'd build a skyscraper with a swimmingpool with my own hands for him...
thnx a lot.

Answer 1

Just figured out a solution by my self:
If you are using a kind of a plugin system and want all your library content (all plugin classes together) to be accessible by any active plugin class. You MUST load
your entry point class of the plugin with your own ClassLoader.
example:
//Write your own ClassLoader
public ArchiveLoader() {
          super();
     public ArchiveLoader(ClassLoader cl) {
          super(cl);
          System.out.println("Initialized by "+getClass().getClassLoader()+" parent: "+cl);
     public synchronized Class loadClass(String name) throws ClassNotFoundException {
          //check if class is loaded          
          Class cl = findLoadedClass(name); 
          if (cl != null)   return cl;
               try {
                    return findClass(name);
               } catch (ClassNotFoundException CNFe) {
                    return getParent().loadClass(name);
     public synchronized Class findClass(String name) throws ClassNotFoundException {     
          if (i can find my class)
               defineClass(...)
          else return getParent().loadClass(name);
class Start {
     public static void main(String...) {
          Class c = new ArchiveLoader().loadClass("plugin_entry_point");
          c.getMethod("go", null).invoke(null, null);
class plugin_entry_point {
     public void go() {
          //use any class you can load.... from wherever
}hoped it helped anyone. At least it would have helped me.