code: @Override
      public boolean endWrite(OutputStream os) {
          boolean endSuccess = false;
          try {
              this.workbook.write(os);
              endSuccess = true;
          } catch (IOException e) {
              e.printStackTrace();
          }
          return endSuccess;
      }
docs: 结束写入并将workbook输出到指定流,
  该方法可以多次调用
  
  @param os 该流需要手动关闭
  @return 写入成功返回true, 否则返回false