Calendar的使用以及活动每月星期的信息

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

/**
 * @author ssqswyf
 * @date 2021/9/17
 */
public class TimeUtil {

    private static int leapYear[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};   //闰年每月天数
    private static int commonYear[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; //平年每月天数

    //判断闰年
    public static boolean isLeapYear(int year){
        return (year%4 == 0 && year%100 != 0) || (year%400 == 0);
    }

    public static void main(String[] args) {
        for (int[] ints : TimeUtil.getWeekInfoInt(2021, 1)) {
            System.out.println("" + ints[0] + " " + ints[1]);
        }
        System.out.println("-------------------------");
        for (String[] strings : TimeUtil.getWeekInfoString(2013, 8)) {
            System.out.println(strings[0] + " " + strings[1]);
        }
    }
    public static List<String[]> getWeekInfoString(int year,int month) {
        List<String[]> weekInfoString = new ArrayList<>();
        List<int[]> weekInfoInt = getWeekInfoInt(year, month);
        for (int[] ints : weekInfoInt) {
            weekInfoString.add(new String[]{thisDayMidnight(year, month, ints[0]),secondDayMidnight(year, month, ints[1])});
        }
        return weekInfoString;


    }


    public static List<int[]> getWeekInfoInt(int year,int month) {
        // 当月天数
        int day = 0;
        // 当月一号是周几
        int weekday =0;
        // 1900.1.1到当前输入日期之间的天数
        int allDays = 0;
        // 当月周数
        int weeks = 0;


        //计算当月天数
        day = isLeapYear(year)?leapYear[month]:commonYear[month];

        //计算距离1900.1.1天数
        for(int i=1900; i<year; i++){
            allDays += isLeapYear(i)?366:365;
        }
        for(int i=1; i<month; i++){
            allDays += isLeapYear(year)?leapYear[i]:commonYear[i];
        }

        //计算当月一号是星期几
        weekday = 1+allDays%7;
        // 计算当月周数
        int lastWeek = (day - (8 - weekday))%7 != 0?1:0;
        weeks = (day - (8 - weekday))/7+2+lastWeek;

        List<int[]> dayList = new ArrayList<>();
        dayList.add(new int[]{1,8-weekday});
        int start = 0;
        int end = 0;
        for (int i = 0;i<weeks-2;i++){
            start = i*7+9-weekday;
            end = start + 6;
            if (end > day){
                end = day;
            }
            dayList.add(new int[]{start,end});
        }
        return dayList;



    }

    /**
     * @return 指定日期凌晨字符串
     */
    public static String thisDayMidnight(int year,int month,int day){
        Calendar calendar = thisDayCalendar(year, month, day);

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String time = sdf.format(calendar.getTime());
        return time;
    }

    /**
     * @return 指定日期第二天凌晨字符串
     */
    public static String secondDayMidnight(int year,int month,int day){
        Calendar calendar = thisDayCalendar(year, month, day);
        calendar.add(Calendar.HOUR,24);

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String time = sdf.format(calendar.getTime());
        return time;
    }

    public static Calendar thisDayCalendar(int year,int month,int day){
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.YEAR, year);
        calendar.set(Calendar.MONTH, month-1);
        calendar.set(Calendar.DAY_OF_MONTH, day);
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);


        return calendar;
    }

    /**
     * @return 当日凌晨字符串
     */
    public static String todayMidnight(){
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(new Date());
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String time = sdf.format(calendar.getTime());
        return time;

    }



    /**
     * @param year
     * @param month
     * @return 月初时间字符串
     */
    public static String monthBegin(Integer year,Integer month){
        Calendar calendar = getMonthBeginCalendar(year, month);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String time = sdf.format(calendar.getTime());
        return time;

    }

    /**
     * @param year
     * @param month
     * @return 月末时间字符串
     */
    public static String monthEnd(Integer year,Integer month){
        Calendar calendar = getMonthBeginCalendar(year, month);
        calendar.add(Calendar.MONTH, 1);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String time = sdf.format(calendar.getTime());
        return time;

    }

    /**
     * @param year
     * @param month
     * @return 月初时间日历格式
     */
    public static Calendar getMonthBeginCalendar(Integer year, Integer month) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.YEAR, year);
        calendar.set(Calendar.MONTH, month-1);
        calendar.set(Calendar.DAY_OF_MONTH, 1);
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        return calendar;
    }



}