java求已知时间的本周，本月，本年的起始时间

有一些项目需要展示本日，本周，本月，本年的相关统计信息，这时就需要根据当前日期（或者所在系统的时间），来确定本周本年本月的起始时间。(java8 以上版本)
代码如下：

package com.jdwa.utill;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjusters;

public class Test1 {
    public static void main(String[] args) {
        String dateTmStr = "2020-09-24 11:20:00";
        String dateStr = "2020-09-24";
        DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        DateTimeFormatter fmtDay = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDateTime dateTm = LocalDateTime.parse(dateTmStr, fmt);
        System.out.println("当前时间:"+fmt.format(dateTm));
        LocalDate date = LocalDate.parse(dateStr,fmtDay);
        System.out.println("当前日期:"+fmtDay.format(date));

        //获取本周起始日期
        System.out.println("本周（周一---->周日）=====================================================");
        LocalDateTime dateWeekFirst = date.with(DayOfWeek.MONDAY).atStartOfDay();
        LocalDateTime dateWeekLast = date.with(TemporalAdjusters.nextOrSame(DayOfWeek.MONDAY)).atStartOfDay().minusSeconds(1L);
        System.out.println("本周一："+fmt.format(dateWeekFirst));
        System.out.println("本周日："+fmt.format(dateWeekLast));
        //如果周日是第一天
        System.out.println("本周（周日---->周六）=====================================================");
        LocalDateTime dateSun = date.with(TemporalAdjusters.previousOrSame(DayOfWeek.SUNDAY)).atStartOfDay();
        LocalDateTime dateSat = date.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY)).atStartOfDay().minusSeconds(1L);
        System.out.println("本周日："+fmt.format(dateSun));
        System.out.println("本周六："+fmt.format(dateSat));


        //获取本月起始日期
        System.out.println("本月==============================================================");
        LocalDateTime dateMonthFirst = date.with(TemporalAdjusters.firstDayOfMonth()).atStartOfDay();
        LocalDateTime datMonthLast = date.with(TemporalAdjusters.firstDayOfNextMonth()).atStartOfDay().minusSeconds(1L);
        System.out.println("本月的第一天："+fmt.format(dateMonthFirst));
        System.out.println("本月最后一天："+fmt.format(datMonthLast));

        //获取本年起始日期
        System.out.println("本年==============================================================");
        LocalDateTime dateYearFirst = date.with(TemporalAdjusters.firstDayOfYear()).atStartOfDay();
        LocalDateTime datYearLast = date.with(TemporalAdjusters.firstDayOfNextYear()).atStartOfDay().minusSeconds(1L);
        System.out.println("本年的第一天："+fmt.format(dateYearFirst));
        System.out.println("本年最后一天："+fmt.format(datYearLast));


    }
}

为了方便手机观看，调整一下

package com.jdwa.utill;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjusters;

public class Test1 {
    public static void main(String[] args) {
        String dateTmStr =
                "2020-09-24 12:20:00";

        String dateStr =
                "2020-09-24";

        DateTimeFormatter fmt =
                DateTimeFormatter.ofPattern
                        ("yyyy-MM-dd HH:mm:ss");

        DateTimeFormatter fmtDay =
                DateTimeFormatter
                        .ofPattern("yyyy-MM-dd");

        LocalDateTime dateTm =
                LocalDateTime.parse
                        (dateTmStr, fmt);

        System.out.println
                ("当前时间:"+
                        fmt.format(dateTm));

        LocalDate date =
                LocalDate.parse
                        (dateStr,fmtDay);

        System.out.println
                ("当前日期:"+
                        fmtDay.format(date));

        //获取本周起始日期
        System.out.println
                ("本周（周一-->周日）==========");

        LocalDateTime dateWeekFirst =
                date.with(DayOfWeek.MONDAY).atStartOfDay();

        LocalDateTime dateWeekLast =
                date.with
                        (TemporalAdjusters.nextOrSame(DayOfWeek.MONDAY))
                        .atStartOfDay()
                        .minusSeconds(1L);

        System.out.println("本周一："+
                fmt.format(dateWeekFirst));

        System.out.println("本周日："+
                fmt.format(dateWeekLast));

        //如果周日是第一天
        System.out.println("本周（周日---->周六）====");
        LocalDateTime dateSun =
                date.with(
                        TemporalAdjusters.
                                previousOrSame
                                        (DayOfWeek.SUNDAY))
                        .atStartOfDay();

        LocalDateTime dateSat =
                date.with
                        (TemporalAdjusters.
                                nextOrSame(DayOfWeek.SUNDAY))
                        .atStartOfDay().minusSeconds(1L);

        System.out.println
                ("本周日："+fmt.format(dateSun));

        System.out.println
                ("本周六："+fmt.format(dateSat));


        //获取本月起始日期
        System.out.println("本月======");

        LocalDateTime dateMonthFirst =
                date.with
                        (TemporalAdjusters.
                                firstDayOfMonth())
                        .atStartOfDay();

        LocalDateTime datMonthLast =
                date.with
                        (TemporalAdjusters.
                                firstDayOfNextMonth())
                        .atStartOfDay().minusSeconds(1L);
        System.out.println
                ("本月的第一天："+fmt.format(dateMonthFirst));
        System.out.println
                ("本月最后一天："+fmt.format(datMonthLast));

        //获取本年起始日期
        System.out.println("本年========");

        LocalDateTime dateYearFirst =
                date.with(TemporalAdjusters
                        .firstDayOfYear())
                        .atStartOfDay();
        LocalDateTime datYearLast =
                date.with(TemporalAdjusters
                        .firstDayOfNextYear())
                        .atStartOfDay().minusSeconds(1L);

        System.out.println
                ("本年的第一天："
                        +fmt.format(dateYearFirst));

        System.out.println
                ("本年最后一天："
                        +fmt.format(datYearLast));


    }
}

运行结果如下：

D:javajdk1.8.0_251injava.exe "...com.jdwa.utill.Test1
当前时间:2020-09-24 12:20:00
当前日期:2020-09-24
本周（周一-->周日）==========
本周一：2020-09-21 00:00:00
本周日：2020-09-27 23:59:59
本周（周日---->周六）====
本周日：2020-09-20 00:00:00
本周六：2020-09-26 23:59:59
本月======
本月的第一天：2020-09-01 00:00:00
本月最后一天：2020-09-30 23:59:59
本年========
本年的第一天：2020-01-01 00:00:00
本年最后一天：2020-12-31 23:59:59

Process finished with exit code 0

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