public ExtClassLoader(File[] dirs) throws IOException 
{
            super(getExtURLs(dirs), null, factory);
}

  void addExtURL(URL url) 
{
            super.addURL(url);
}

 public String findLibrary(String name) 
{
            name = System.mapLibraryName(name);
            URL[] urls = super.getURLs();
            File prevDir = null;
            for (int i = 0; i <  urls.length; i++) {
                // Get the ext directory from the URL
                File dir = new File(urls[i].getPath()).getParentFile();
                if (dir != null && !dir.equals(prevDir)) {
                    // Look in architecture-specific subdirectory first
                    // Read from the saved system properties to avoid deadlock
                    String arch = VM.getSavedProperty("os.arch");
                    if (arch != null) {
                        File file = new File(new File(dir, arch), name);
                        if (file.exists()) {
                            return file.getAbsolutePath();
                        }
                    }
                    // Then check the extension directory
                    File file = new File(dir, name);
                    if (file.exists()) {
                        return file.getAbsolutePath();
                    }
                }
                prevDir = dir;
            }
            return null;
}

 public static ExtClassLoader getExtClassLoader() throws IOException 
{
            final File[] dirs = getExtDirs();
            try {
                // Prior implementations of this doPrivileged() block supplied
                // aa synthesized ACC via a call to the private method
                // ExtClassLoader.getContext().
                return AccessController.doPrivileged(
                    new PrivilegedExceptionAction< ExtClassLoader >() {
                        public ExtClassLoader run() throws IOException {
                            int len = dirs.length;
                            for (int i = 0; i <  len; i++) {
                                MetaIndex.registerDirectory(dirs[i]);
                            }
                            return new ExtClassLoader(dirs);
                        }
                    });
            } catch (java.security.PrivilegedActionException e) {
                throw (IOException) e.getException();
            }
}

create an ExtClassLoader. The ExtClassLoader is created within a context that limits which files it can read