code: public static ExtractRegular getInstance(String serverUrl, String redisHost, int redisPort) {
          if (extractRegular != null) {
              return extractRegular;
          }
          synchronized (ExtractRegular.class) {
              if (extractRegular == null) {
                  extractRegular = new ExtractRegular();
                  //订阅Redis服务器Channel：pr，当规则改变的时候会收到通知消息CHANGE并重新初始化规则集合
                  extractRegular.subscribeRedis(redisHost, redisPort, serverUrl);
                  //初始化抽取规则
                  extractRegular.init(serverUrl);
              }
          }
          return extractRegular;
      }
docs: 获取抽取规则实例
  
  @param serverUrl 配置管理WEB服务器的抽取规则下载地址
  @param redisHost Redis服务器主机
  @param redisPort Redis服务器端口
  @return 抽取规则实例