code: public static ClassLoader getAppClassLoader(String appName) {
          ClassLoader appClassLoader = APPNAME_CLASSLOADER_MAP.get(appName);
          if (appClassLoader == null) {
              return ClassLoaderUtils.getCurrentClassLoader();
          } else {
              return appClassLoader;
          }
      }
docs: 得到服务的自定义ClassLoader
  
  @param appName 应用名
  @return 应用级别ClassLoader