public static boolean isValid(File f) {
        if (f.isDirectory()) {
            return false;
        }

        String extension = FileTools.getExtension(f);
        if (extension != null) {
            if (extension.equals(".zip") ||
                extension.equals(".tar") ||
                extension.equals(".rar") ||
                extension.equals(".sskin") ||
                extension.equals(".jar")) {
                    return true;
            } else {
                return false;
            }
        }

        return false;
    }