用POI导出xls之后，模版自带的求和函数不计算
格式是这样设置
HSSFCellStyle cellStyleString = wb.createCellStyle();
cellStyleString.setAlignment(HSSFCellStyle.ALIGN_CENTER);
cellStyleString.setVerticalAlignment(HSSFCellStyle.VERTICAL_CENTER);
cellStyleString.setBorderBottom(HSSFCellStyle.BORDER_THIN);// 设置边框
cellStyleString.setBorderLeft(HSSFCellStyle.BORDER_THIN);
cellStyleString.setBorderRight(HSSFCellStyle.BORDER_THIN);
cellStyleString.setBorderTop(HSSFCellStyle.BORDER_THIN);
cellStyleString.setWrapText(true);