需求描述：

根据两个日期，计算两日期之前所有日期
根据两个月份，计算出两个月份之间所有月份

解决方案：

package com.ems.openflow.utils;import java.text.DecimalFormat;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 CountDate {    private static transient int gregorianCutoverYear = 1582;    /** 闰年中每月天数 */    private static final int[] DAYS_P_MONTH_LY= {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};    /** 非闰年中每月天数 */    private static final int[] DAYS_P_MONTH_CY= {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};    /** 代表数组里的年、月、日 */    private static final int Y = 0, M = 1, D = 2;    /**     * 将代表日期的字符串分割为代表年月日的整形数组      * @param date     * @return     */    public static int[] splitYMD(String date){ date = date.replace("-", ""); int[] ymd = {0, 0, 0}; ymd[Y] = Integer.parseInt(date.substring(0, 4)); ymd[M] = Integer.parseInt(date.substring(4, 6)); ymd[D] = Integer.parseInt(date.substring(6, 8)); return ymd;    }    /**     * 检查传入的参数代表的年份是否为闰年      * @param year     * @return     */    public static boolean isLeapYear(int year) { return year >= gregorianCutoverYear ?  ((year%4 == 0) && ((year%100 != 0) || (year%400 == 0))) : (year%4 == 0);    }    /**     * 日期加1天      * @param year     * @param month     * @param day     * @return     */    private static int[] addOneDay(int year, int month, int day){ if(isLeapYear( year )){     day++;     if( day > DAYS_P_MONTH_LY[month -1 ] ){  month++;  if(month > 12){      year++;      month = 1;  }  day = 1;     } }else{     day++;     if( day > DAYS_P_MONTH_CY[month -1 ] ){  month++;  if(month > 12){      year++;      month = 1;  }  day = 1;     } } int[] ymd = {year, month, day}; return ymd;    }    /**     * 将不足两位的月份或日期补足为两位      * @param decimal     * @return     */    public static String formatMonthDay(int decimal){ DecimalFormat df = new DecimalFormat("00"); return df.format( decimal );    }    /**     * 将不足四位的年份补足为四位      * @param decimal     * @return     */    public static String formatYear(int decimal){ DecimalFormat df = new DecimalFormat("0000"); return df.format( decimal );    }    /**     * 计算两个日期之间相隔的天数      * @param begin     * @param end     * @return     * @throws ParseException     */    public static long countDay(String begin,String end){ SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd"); Date beginDate , endDate; long day = 0; try {     beginDate= format.parse(begin);     endDate=  format.parse(end);     day=(endDate.getTime()-beginDate.getTime())/(24*60*60*1000); } catch (ParseException e) {     e.printStackTrace(); } return day;    }    /**     * 以循环的方式计算日期      * @param beginDate endDate      * @param days     * @return     */    public static List getEveryday(String beginDate , String endDate){ long days = countDay(beginDate, endDate); int[] ymd = splitYMD( beginDate ); List everyDays = new ArrayList(); everyDays.add(beginDate); for(int i = 0; i < days; i++){     ymd = addOneDay(ymd[Y], ymd[M], ymd[D]);     everyDays.add(formatYear(ymd[Y])+"-"+formatMonthDay(ymd[M])+"-"+formatMonthDay(ymd[D])); } return everyDays;    }    /**     * 计算日期内所有月份     * @param beginDate     * @param endDate     * @return     */    public static List getEveryMonth(String beginDate , String endDate) throws ParseException {  Date start = new SimpleDateFormat("yyyy-MM").parse(beginDate); Date end = new SimpleDateFormat("yyyy-MM").parse(endDate); Calendar calendar = Calendar.getInstance(); calendar.setTime(start); // 获取开始年份和开始月份 int startYear = calendar.get(Calendar.YEAR); int startMonth = calendar.get(Calendar.MONTH); // 获取结束年份和结束月份 calendar.setTime(end); int endYear = calendar.get(Calendar.YEAR); int endMonth = calendar.get(Calendar.MONTH); // List list = new ArrayList(); for (int i = startYear; i <= endYear; i++) {     String date = "";     if (startYear == endYear) {  for (int j = startMonth; j <= endMonth; j++) {      if (j < 9) {   date = i + "-0" + (j + 1);      } else {   date = i + "-" + (j + 1);      }      list.add(date);  }     } else {  if (i == startYear) {      for (int j = startMonth; j < 12; j++) {   if (j < 9) {date = i + "-0" + (j + 1);   } else {date = i + "-" + (j + 1);   }   list.add(date);      }  } else if (i == endYear) {      for (int j = 0; j <= endMonth; j++) {   if (j < 9) {date = i + "-0" + (j + 1);   } else {date = i + "-" + (j + 1);   }   list.add(date);      }  } else {      for (int j = 0; j < 12; j++) {   if (j < 9) {date = i + "-0" + (j + 1);   } else {date = i + "-" + (j + 1);   }   list.add(date);      }  }     } } return list;     }    /** 获取一个月的最后一天 */    public static String getLastDay(String date) throws ParseException { SimpleDateFormat d = new SimpleDateFormat("yyyy-MM"); Date da = null; da = d.parse(date); SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd"); Calendar calendar = Calendar.getInstance(); calendar.setTime(da); int lastDays = calendar.getActualMaximum(Calendar.DAY_OF_MONTH); calendar.set(Calendar.DAY_OF_MONTH, lastDays); return df.format(calendar.getTime());    }    /** 获取一个月的第一天 */    public static String getFirstDay(String date) throws ParseException { SimpleDateFormat d = new SimpleDateFormat("yyyy-MM"); Date da = null; da = d.parse(date); SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd"); Calendar calendar = Calendar.getInstance(); calendar.setTime(da); //calendar.add(Calendar.MONTH, -1); calendar.set(Calendar.DAY_OF_MONTH, 1); String time = df.format(calendar.getTime()); return time;    }    public static void main(String[] args) throws ParseException { List list1 = CountDate.getEveryday("2021-07-01", "2021-09-02"); for (String result : list1) {     System.out.println(result); } List list2 = CountDate.getEveryMonth("2021-02", "2021-09"); for (String result : list2) {     System.out.println(result); }    }}

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