poi 对cell的数值转换

注意数值型转换：

private static String getCellValue(Cell c) {
        String o = null;
        switch (c.getCellType()) {
        case Cell.CELL_TYPE_BLANK:
            o = "";
            break;
        case Cell.CELL_TYPE_BOOLEAN:
            o = String.valueOf(c.getBooleanCellValue());
            break;
        case Cell.CELL_TYPE_FORMULA:
            o = String.valueOf(c.getCellFormula());
            break;
        case Cell.CELL_TYPE_NUMERIC:
            if (HSSFDateUtil.isCellDateFormatted(c)) {
                double d = c.getNumericCellValue();
                Date date = HSSFDateUtil.getJavaDate(d);
                SimpleDateFormat dformat = new SimpleDateFormat("yyyy-MM-dd");
                o = dformat.format(date);
            }
            else {
                NumberFormat nf = NumberFormat.getInstance();
                nf.setGroupingUsed(false);// true时的格式：1,234,567,890
                o = nf.format(c.getNumericCellValue());//
            }
            break;
        case Cell.CELL_TYPE_STRING:
            o = c.getStringCellValue();
            break;
        default:
            o = null;
            break;
        }
        return o;
    }