code: public long skip(long n) throws IOException {
          int s = cache.size();
          if(s > 0){
              if(s < n){
                  n = n - s;
              } else {
                  for(int i = 0; i < n; i ++){
                      cache.poll();
                  }
                  return n;
              }
          }
          return super.skip(n) + s;
      }
docs: 跳过和丢弃输入流中的数据