java按照月份把一个时间段拆分成多个时间区间并返回相差天数

package com.mw.web.common.utils;

import com.mw.web.param.KeyValueForDate;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

public class SplitDateUtil {
    /**
     * 根据一段时间区间，按月份拆分成多个时间段
     * @param startDate 开始日期
     * @param endDate  结束日期
     * @return
     */
    public static List<KeyValueForDate> getKeyValueForDate(String startDate,String endDate) {
        List<KeyValueForDate> list = null;
        try {
            list = new ArrayList<KeyValueForDate>();
            String firstDay = "";
            String lastDay = "";
            Date d1 = new SimpleDateFormat("yyyy-MM-dd").parse(startDate);// 定义起始日期
            Date d2 = new SimpleDateFormat("yyyy-MM-dd").parse(endDate);// 定义结束日期
            Calendar dd = Calendar.getInstance();// 定义日期实例
            dd.setTime(d1);// 设置日期起始时间
            Calendar cale = Calendar.getInstance();
            Calendar c = Calendar.getInstance();
            c.setTime(d2);
            int startDay = d1.getDate();
            int endDay = d2.getDate();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            KeyValueForDate keyValueForDate = null;
            while (dd.getTime().before(d2)) {// 判断是否到结束日期
                keyValueForDate = new KeyValueForDate();
                cale.setTime(dd.getTime());

                if(dd.getTime().equals(d1)){
                    cale.set(Calendar.DAY_OF_MONTH, dd
                            .getActualMaximum(Calendar.DAY_OF_MONTH));
                    lastDay = sdf.format(cale.getTime());
                    keyValueForDate.setStartDate(sdf.format(d1));
                    keyValueForDate.setEndDate(lastDay);
                    keyValueForDate.setDays(differentDays(d1,sdf.parse(lastDay)));

                }else if(dd.get(Calendar.MONTH) == d2.getMonth() && dd.get(Calendar.YEAR) == c.get(Calendar.YEAR)){
                    cale.set(Calendar.DAY_OF_MONTH,1);//取第一天
                    firstDay = sdf.format(cale.getTime());

                    keyValueForDate.setStartDate(firstDay);
                    keyValueForDate.setEndDate(sdf.format(d2));
                    keyValueForDate.setDays(differentDays(sdf.parse(firstDay),d2));
                }else {
                    cale.set(Calendar.DAY_OF_MONTH,1);//取第一天
                    firstDay = sdf.format(cale.getTime());

                    cale.set(Calendar.DAY_OF_MONTH, dd
                            .getActualMaximum(Calendar.DAY_OF_MONTH));
                    lastDay = sdf.format(cale.getTime());

                    keyValueForDate.setStartDate(firstDay);
                    keyValueForDate.setEndDate(lastDay);
                    keyValueForDate.setDays(differentDays(sdf.parse(firstDay),sdf.parse(lastDay)));

                }
                list.add(keyValueForDate);
                dd.add(Calendar.MONTH, 1);// 进行当前日期月份加1

            }

            if(endDay<startDay){
                keyValueForDate = new KeyValueForDate();

                cale.setTime(d2);
                cale.set(Calendar.DAY_OF_MONTH,1);//取第一天
                firstDay = sdf.format(cale.getTime());

                keyValueForDate.setStartDate(firstDay);
                keyValueForDate.setEndDate(sdf.format(d2));
                keyValueForDate.setDays(differentDays(sdf.parse(firstDay),d2));
                list.add(keyValueForDate);
            }
        } catch (ParseException e) {
            return null;
        }
        return list;
    }

    /**
     * date2比date1多的天数
     * @param date1
     * @param date2
     * @return
     */
    public static int differentDays(Date date1,Date date2)
    {
        Calendar cal1 = Calendar.getInstance();
        cal1.setTime(date1);

        Calendar cal2 = Calendar.getInstance();
        cal2.setTime(date2);
        int day1= cal1.get(Calendar.DAY_OF_YEAR);
        int day2 = cal2.get(Calendar.DAY_OF_YEAR);

        int year1 = cal1.get(Calendar.YEAR);
        int year2 = cal2.get(Calendar.YEAR);
        if(year1 != year2)   //不同一年
        {
            int timeDistance = 0 ;
            for(int i = year1 ; i < year2 ; i ++)
            {
                if(i%4==0 && i%100!=0 || i%400==0)    //闰年
                {
                    timeDistance += 366;
                }
                else    //不是闰年
                {
                    timeDistance += 365;
                }
            }
            /*+1包含当天*/
            return timeDistance + (day2-day1+1) ;
        }
        else    //同一年
        {
            /*+1包含当天*/
            return day2-day1+1;
        }
    }
}

public class KeyValueForDate {
    private String startDate;
    private String endDate;
    private Integer days;
    public String getStartDate() {
        return startDate;
    }
    public void setStartDate(String startDate) {
        this.startDate = startDate;
    }
    public String getEndDate() {
        return endDate;
    }
    public void setEndDate(String endDate) {
        this.endDate = endDate;
    }

    public Integer getDays() {
        return days;
    }

    public void setDays(Integer days) {
        this.days = days;
    }
}

public static void main(String args[]){
   String minDate = "2020-12-27";
   String maxDate = "2021-05-01";
   List<KeyValueForDate> list = SplitDateUtil.getKeyValueForDate(minDate,maxDate);
   System.out.println("开始日期--------------结束日期--------------相差天数");
   for(KeyValueForDate date : list){
      System.out.println(date.getStartDate()+"-----"+date.getEndDate()+"-----"+date.getDays());
   }

}