Calculate the difference in years, months and days between two dates, taking leap years into consideration

Calculate the difference in years, months and days between two dates under Java 8, taking into account leap years and ordinary years

  //    java 计算两个日期相差几年几月几天，考虑闰年平年
    public void calculateDifference(String startDade, String endDate) {

         Calendar calendar1 = Calendar.getInstance(); // 第一个日期，默认当前日期
        Calendar calendar2 = Calendar.getInstance(); // 第二个日期，默认当前日期

        // 设置第一个日期的年、月、日
        calendar1.set(Calendar.YEAR, RexgUtil.getYMD(startDade)[0]);
        calendar1.set(Calendar.MONTH, RexgUtil.getYMD(startDade)[1]);
        calendar1.set(Calendar.DAY_OF_MONTH, RexgUtil.getYMD(startDade)[2]);

        if (null != endDate) {
            calendar2.set(Calendar.YEAR, RexgUtil.getYMD(endDate)[0]);
            calendar2.set(Calendar.MONTH, RexgUtil.getYMD(endDate)[1]);
            calendar2.set(Calendar.DAY_OF_MONTH, RexgUtil.getYMD(endDate)[2]);
        }
        int yearDifference = calendar2.get(Calendar.YEAR) - calendar1.get(Calendar.YEAR);
        int monthDifference = calendar2.get(Calendar.MONTH)+(null != endDate ? 0 : 1) - calendar1.get(Calendar.MONTH);
        int dayDifference = calendar2.get(Calendar.DAY_OF_MONTH) - calendar1.get(Calendar.DAY_OF_MONTH);

        // 考虑日期超出状况，需要从年或者月借位
        if (dayDifference < 0) {
            monthDifference -= 1;
            int month = calendar1.get(Calendar.MONTH);
            int year = calendar1.get(Calendar.YEAR);

            // 判断是否为2月，考虑闰年平年
            if (month == Calendar.FEBRUARY) {
                if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
                    dayDifference += 29;
                } else {
                    dayDifference += 28;
                }
            } else if (month == Calendar.APRIL ||
                    month == Calendar.JUNE ||
                    month == Calendar.SEPTEMBER ||
                    month == Calendar.NOVEMBER) {
                dayDifference += 30;
            } else {
                dayDifference += 31;
            }
        }

        if (yearDifference <= 0) {
            // 考虑闰年的情况
            if (monthDifference < 0 || (monthDifference == 0 && dayDifference < 0)) {
                yearDifference--;
                monthDifference += 12;
            }

            dayDifference = monthDifference <=0 ? (dayDifference+1) : dayDifference;
        }


        System.out.println("Years: " + yearDifference);
        System.out.println("Months: " + monthDifference);
        System.out.println("Days: " + dayDifference);

    }



public class RexgUtil {

    public static int[] getYMD(String yyyymmddStr) {
        int[] ymd= new int[3];
//        String input = "2023年08月03日";

        // 使用正则表达式匹配年、月、日
        String pattern = "([0-9]{4})年([0-9]{2})月([0-9]{2})日";
        Pattern regex = Pattern.compile(pattern);
        Matcher matcher = regex.matcher(yyyymmddStr);

        if (matcher.find()) {
            String year = matcher.group(1);
            String month = matcher.group(2);
            String day = matcher.group(3);

//            System.out.println("年: " + year);
//            System.out.println("月: " + month);
//            System.out.println("日: " + day);

            ymd[0] = Integer.parseInt(year);
            ymd[1] = Integer.parseInt(month);
            ymd[2] = Integer.parseInt(day);
        }
        return ymd;
    }
}

For example: the difference from January 9, 2015 to present

The code above jdk8 is more concise:

import java.time.LocalDate;
import java.time.Period;
import java.time.temporal.ChronoUnit;

public class Main {
    public static void main(String[] args) {
        //设置开始日期和结束日期
        LocalDate startDate = LocalDate.of(2010, 1, 1);
        LocalDate endDate = LocalDate.of(2020, 9, 20);

        //按整月计算差值
        long monthsBetween = ChronoUnit.MONTHS.between(startDate, endDate);
        long years = monthsBetween / 12;
        long remainMonths = monthsBetween % 12;

        //按天计算差值
        long daysBetween = ChronoUnit.DAYS.between(startDate.plusMonths(monthsBetween), endDate);
        
        System.out.println("相差" + years + "年" + remainMonths + "月" + daysBetween + "天");
        
      //或者你也可以使用Period做更精确的计算
        Period period = Period.between(startDate, endDate);
        System.out.println("相差" + period.getYears() + "年" + period.getMonths() + "月" + period.getDays() + "天");
    }
}