转：Java 计算2个时间相差多少年，多少个月，多少天的几种方式

    @Data
    @Builder
    public static class DayCompare{
        private int year;
        private int month;
        private int day;
    }

/**
 * 计算2个日期之间相差的  相差多少年月日
 * 比如：2011-02-02 到  2017-03-02 相差 6年，1个月，0天
 * @param fromDate
 * @param toDate
 * @return
 */
public static DayCompare dayComparePrecise(Date fromDate,Date toDate){
    Calendar  from  =  Calendar.getInstance();
    from.setTime(fromDate);
    Calendar  to  =  Calendar.getInstance();
    to.setTime(toDate);

    int fromYear = from.get(Calendar.YEAR);
    int fromMonth = from.get(Calendar.MONTH);
    int fromDay = from.get(Calendar.DAY_OF_MONTH);

    int toYear = to.get(Calendar.YEAR);
    int toMonth = to.get(Calendar.MONTH);
    int toDay = to.get(Calendar.DAY_OF_MONTH);
    int year = toYear  -  fromYear;
    int month = toMonth  - fromMonth;
    int day = toDay  - fromDay;
    return DayCompare.builder().day(day).month(month).year(year).build();
}

/**
 * 计算2个日期之间相差的  以年、月、日为单位，各自计算结果是多少
 * 比如：2011-02-02 到  2017-03-02
 *                                以年为单位相差为：6年
 *                                以月为单位相差为：73个月
 *                                以日为单位相差为：2220天
 * @param fromDate
 * @param toDate
 * @return
 */
public static DayCompare dayCompare(Date fromDate,Date toDate){
    Calendar  from  =  Calendar.getInstance();
    from.setTime(fromDate);
    Calendar  to  =  Calendar.getInstance();
    to.setTime(toDate);
    //只要年月
    int fromYear = from.get(Calendar.YEAR);
    int fromMonth = from.get(Calendar.MONTH);

    int toYear = to.get(Calendar.YEAR);
    int toMonth = to.get(Calendar.MONTH);

    int year = toYear  -  fromYear;
    int month = toYear *  12  + toMonth  -  (fromYear  *  12  +  fromMonth);
    int day = (int) ((to.getTimeInMillis()  -  from.getTimeInMillis())  /  (24  *  3600  *  1000));
    return DayCompare.builder().day(day).month(month).year(year).build();
}

/**
 * 计算2个日期相差多少年
 * 列：2011-02-02  ~  2017-03-02 大约相差 6.1 年
 * @param fromDate
 * @param toDate
 * @return
 */
public static String yearCompare(Date fromDate,Date toDate){
    DayCompare result = dayComparePrecise(fromDate, toDate);
    double month = result.getMonth();
    double year = result.getYear();
    //返回2位小数，并且四舍五入
    DecimalFormat df = new DecimalFormat("######0.0");
    return df.format(year + month / 12);
}