code: static void register(Class<? extends URLStreamHandler> handlerClass) {
      checkArgument("Handler".equals(handlerClass.getSimpleName()));
  
      String pkg = handlerClass.getPackage().getName();
      int lastDot = pkg.lastIndexOf('.');
      checkArgument(lastDot > 0, "package for Handler (%s) must have a parent package", pkg);
  
      String parentPackage = pkg.substring(0, lastDot);
  
      String packages = System.getProperty(JAVA_PROTOCOL_HANDLER_PACKAGES);
      if (packages == null) {
        packages = parentPackage;
      } else {
        packages += "|" + parentPackage;
      }
      System.setProperty(JAVA_PROTOCOL_HANDLER_PACKAGES, packages);
    }
docs: Generic method that would allow registration of any properly placed {@code Handler} class.