code: public static ProxyClassLoader convertClassloader(ClassLoader loader) {
          if (loader == null) {
              return ProxyClient.DEFAULT_LOADER;
          } else if (loader instanceof ProxyClassLoader) {
              return (ProxyClassLoader) loader;
          } else {
              return new ProxyClassLoader(loader);
          }
      }
docs: 转换classloader
  @param loader 原classloader
  @return 转换后的classloader