POI读取excel日期（数字转化成日期格式）

Calendar calendar = new GregorianCalendar(1900,0,-1);
Date d = calendar.getTime();
if (null != serviceDateStr){
	String constant = StringUtils.isBlank(serviceDateStr) ? "" : serviceDateStr;
	if (!"".equals(serviceDateStr)){
		serviceDate = DateUtils.addDays(d,Integer.valueOf(constant));
	}
}