code: private void autoLogin() {
          String file = bot.config().assetsDir() + "/login.json";
          try {
              HotReload hotReload = WeChatUtils.fromJson(new FileReader(file), HotReload.class);
              hotReload.reLogin(bot);
          } catch (FileNotFoundException e) {
              this.login(false);
          }
      }
docs: 自动登录