DateUtils日期工具类

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

public class DateUtils {
    //日期转字符串
    public static String dateStr(LocalDate date){
        return date.toString();
    }

    /**
     * 字符串转时间
     * @param t  "2021-03-03"
     * @return
     */
    public static LocalDate parse(String t) {
        return LocalDate.parse(t);
    }

    /**
     * 时间计算
     * @param date  不传则默认今天
     * @param day
     * @return
     */
    public static LocalDate calcDate(LocalDate date, int day) {
        return date.plusDays(day);
    }
    public static LocalDate calcDate(int day) {
        return LocalDate.now().plusDays(day);
    }

    /**
     * 计算两个日期之间相隔几天
     * @param before 开始 "2021-03-03"
     * @param after 结束 "2021-03-10"
     * @return 7
     */
    public static Integer duration(LocalDate before, LocalDate after){
        return Period.between(before, after).getDays();
    }

    /**
     * 获取指定月最后一天
     * @param date 不传默认当月
     * @return
     */
    public static LocalDate getLastDayOfMonth(LocalDate date){
        return date.with(TemporalAdjusters.lastDayOfMonth());
    }
    public static LocalDate getLastDayOfMonth(){
        return LocalDate.now().with(TemporalAdjusters.lastDayOfMonth());
    }
    /**
     * 获取指定月第一天
     * @param date 不传默认当月
     * @return
     */
    public static LocalDate getFirstDayOfMonth(LocalDate date){
        return date.with(TemporalAdjusters.firstDayOfMonth());
    }
    public static LocalDate getFirstDayOfMonth(){
        return LocalDate.now().with(TemporalAdjusters.firstDayOfMonth());
    }

    public static void main(String[] args) {
        LocalDate now = LocalDate.now();
        System.out.println(now.toEpochDay());

        System.out.println(DateUtils.duration(DateUtils.parse("2021-03-13"),DateUtils.parse("2021-03-10")));
    }
}