java8获取本周本月第一天和最后一天

本月

LocalDate today = LocalDate.now();
//本月的第一天
LocalDate firstday = LocalDate.of(today.getYear(),today.getMonth(),1);
//本月的最后一天
LocalDate lastDay =today.with(TemporalAdjusters.lastDayOfMonth());
System.out.println("本月的第一天" + firstday);
System.out.println("本月的最后一天" + lastDay);

输出：

本月的第一天2020-09-01
本月的最后一天2020-09-30

本周

LocalDate today = LocalDate.now();
System.out.println("本周第一天："+date2Str(getStartDayOfWeek(today)));
System.out.println("本周最后一天："+date2Str(getEndDayOfWeek(today)));

public static String date2Str(Date date) {
		return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(date);
	}
	
public static Date getStartDayOfWeek(TemporalAccessor date) {
       TemporalField fieldIso = WeekFields.of(DayOfWeek.MONDAY, 1).dayOfWeek();
       LocalDate localDate = LocalDate.from(date);
       localDate = localDate.with(fieldIso, 1);
       return Date.from(localDate.atStartOfDay(ZoneId.systemDefault()).toInstant());
   }

public static Date getEndDayOfWeek(TemporalAccessor date) {
	TemporalField fieldIso = WeekFields.of(DayOfWeek.MONDAY, 1).dayOfWeek();
       LocalDate localDate = LocalDate.from(date);
       localDate = localDate.with(fieldIso, 7);
       return Date.from(localDate.atStartOfDay(ZoneId.systemDefault()).toInstant());
   }

输出：

本周第一天：2020-09-07 00:00:00
本周最后一天：2020-09-13 00:00:00