java 比较日期早晚
public boolean compareDate(String time1,String time2) throws ParseException {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date a = sdf.parse(time1);
Date b = sdf.parse(time2);
//Date类的一个方法,如果a早于b返回true,否则返回false
return a.before(b);
}