提供了非常多处理日期相关的函数：

使用示例：

    /**
     * JCccc
     * @param args
     */
    public static void main(String[] args) {
        DateTimeFormatter pattern = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDateTime now = LocalDateTime.now();
        //获取当月第一天
        System.out.println("当月第一天：" + now.with(TemporalAdjusters.firstDayOfMonth()).format(pattern));
        //获取下月第一天
        System.out.println("下月第一天：" + now.with(TemporalAdjusters.firstDayOfNextMonth()).format(pattern));
        //获取明年第一天
        System.out.println("明年第一天：" + now.with(TemporalAdjusters.firstDayOfNextYear()).format(pattern));
        //获取本年第一天
        System.out.println("本年第一天：" + now.with(TemporalAdjusters.firstDayOfYear()).format(pattern));
        //获取当月最后一天
        System.out.println("当月最后一天：" + now.with(TemporalAdjusters.lastDayOfMonth()).format(pattern));
        //获取本年最后一天
        System.out.println("本年最后一天：" + now.with(TemporalAdjusters.lastDayOfYear()).format(pattern));
        //获取当月第三周星期五
        System.out.println("当月第三周星期五：" + now.with(TemporalAdjusters.dayOfWeekInMonth(3, DayOfWeek.FRIDAY)).format(pattern));
        //获取上周一
        System.out.println("上周一：" + now.with(TemporalAdjusters.previous(DayOfWeek.MONDAY)).format(pattern));
        //获取下周日
        System.out.println("下周日：" + now.with(TemporalAdjusters.next(DayOfWeek.SUNDAY)).format(pattern));
    }

效果：