poi 导出excel文件，可以彻底解决无法打开Excel文件问题

Java代码为：

public static void main(String[] args) throws IOException {
   Date now=new Date();
   SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMddHHmmss");
   String localname=dateFormat.format(now);
   String xlsxPath = "d:\\"+ localname + ".xls";
   HSSFWorkbook workBook = new HSSFWorkbook();
   OutputStream fos = null;
   try {//增加一个Sheet的对象
      HSSFSheet sheet = workBook.createSheet("sheet1");
      HSSFRow row = sheet.createRow(0);
      row.createCell(0).setCellValue("aaaaaaaa");
      fos = new FileOutputStream(xlsxPath);
   } catch (FileNotFoundException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
   }
   workBook.write(fos);
   fos.close();
}

注意： 是.xls，不支持.xlsx