import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Enumeration;
import java.util.LinkedList;
import java.util.List;
import java.util.jar.JarFile;
import java.util.zip.ZipEntry;

public class CheckJar {

    public static class MyClassLoader extends URLClassLoader {
        private File jarFile;
        
        public MyClassLoader(String _sJar) throws MalformedURLException {
            super(new URL[0]);
            jarFile = new File(_sJar);
            addURL(jarFile.toURL());
        }
        
        public List findClasses(String ifName) throws IOException, ClassNotFoundException {
            List classList = new LinkedList();
            JarFile jf = new JarFile(jarFile);
            Enumeration e = jf.entries();
            while(e.hasMoreElements()) {
                ZipEntry z = (ZipEntry)e.nextElement();
                
                if(z.getName().endsWith(".class")) {
                        String className = z.getName().replace('\\', '.').replace('/','.');
                        try {
                                // load the class (problably needs catching because dependencies may be unresolvable
                                Class c = loadClass(className.substring(0, className.length() - ".class".length()));
                                Class interfaces[] = c.getInterfaces();
                                for(int i = 0 ; i < interfaces.length; i++) {
                                // you may want to do this recursively (in case interfaces were extended)
                                    if(interfaces[i].getName().equals(ifName)) {
                                        // jay we got a plugin
                                        System.out.println("Usable class : " + className);
                                        classList.add(className);
                                    }
                                }
                        } catch(Throwable t) {
                            System.out.println("problem with : " + className);
                        }
                }
            }
            return classList;
        }                
    }
    
    public static void main(String[] args) throws Exception {
        MyClassLoader cl = new MyClassLoader(args[0]);
        Thread.currentThread().setContextClassLoader( cl );
        List classList = cl.findClasses(args[1]);
    }
    
}