c#(winform,webform通用)利用npoi将xls文件复制为xlsx文件（excel的修改，保存，包括excel2003-office2007+的处理）

   public void writeExcel(string readExcelPath, string writeExcelPath)
        {
            //需要读取的excel信息
            FileStream file = new FileStream(readExcelPath, FileMode.Open, FileAccess.Read);
            HSSFWorkbook book = new HSSFWorkbook(file);
            HSSFSheet sheet = (HSSFSheet)book.GetSheetAt(0);

            //需要写入的excel信息  XSSFWorkbook是处理xlsx即excel2007+以上文件的
            FileStream writeFile = new FileStream(writeExcelPath, FileMode.Open, FileAccess.Read);
            XSSFWorkbook writeBook = new XSSFWorkbook(writeFile);
            XSSFSheet writeSheet = (XSSFSheet)writeBook.GetSheetAt(0);


            for (int i = 0; i < sheet.LastRowNum + 1; i++)
            {
                //获取第i行，得到对象
                IRow row = sheet.GetRow(i);
                //新建第i行，并返回得到的对象
                IRow writeRow = writeSheet.CreateRow(i);
                for (int j = 0; j < row.LastCellNum+1; j++)
                {
                    ICell cell = row.GetCell(j);
                    if (cell == null)
                    {
                        break;
                    }

                    //这句话是设置单元格类型为string类型，否则如果单元格内容为numeric的话，会抛出异常
                    row.GetCell(j).SetCellType(CellType.STRING);
                    string readValue = sheet.GetRow(i).GetCell(j).StringCellValue;

                    if (string.IsNullOrEmpty(readValue))
                    {
                        continue;
                    }
                    //新建第i行，第j列
                    writeRow.CreateCell(j);
                    writeSheet.GetRow(i).GetCell(j).SetCellValue(readValue);
                    textBox3.Text += readValue;
                }
            }
            //保存的地址，我做了处理，不让他保存在我选择的地址上，实际上不处理的话也没有问题
            string savePath = textBox2.Text.Replace(".xlsx","_bak.xlsx");
            FileStream saveFile = new FileStream(savePath, FileMode.Create);
            //将处理后的文件保存到新文件中去
            writeBook.Write(saveFile);
            saveFile.Close();
            file.Close();
            MessageBox.Show("处理excel完毕");
        }