记录每一天，Java.time 中时间日期的处理。

LocalDate 处理日期

　　在学习 jdk1.8 中其中有一个对日期，时间处理很棒的方法。妈妈再也不用担心我不会处理日期，时间了。

/**
 * 在 jdk1.8 中 时间 日期 的处理 java.time
 */
@Slf4j
public class dateTest {


    @Test
    public void test01() {
        // 创建指定的日期时间
        LocalDate date1 = LocalDate.of(2021, 05, 05);
        System.out.println(date1);

        // 获取当前的日期 默认 yyyy-mm-dd
        LocalDate now = LocalDate.now();
        System.out.println("当前日期:" + now);

        // 取上月 2023-06-23
        LocalDate last_month = LocalDate.of(now.getYear(), now.getMonthValue() - 1, now.getDayOfMonth());
        System.out.println("1.上月：" + last_month);
        LocalDate last_month2 = now.minusMonths(1);
        System.out.println("2.上月：" + last_month2);

        //取下月
        LocalDate next_month = now.plusMonths(1);
        System.out.println("下月："+next_month.toString());

        //取前一天
        LocalDate last_day = LocalDate.of(now.getYear(), now.getMonthValue(), now.getDayOfMonth() - 1);
        System.out.println("1.上一天："+last_day);
        LocalDate last_day2 = now.minusDays(1);
        System.out.println("2.上一天："+last_day2);

        //取后一天
        LocalDate next_day = now.plusDays(1);
        System.out.println("下一天"+next_day);

        //取上一年
        LocalDate last_year = LocalDate.of(now.getYear()-1, now.getMonthValue(), now.getDayOfMonth());
        System.out.println("1.上一年："+last_year);
        LocalDate last_year2 = now.minusYears(1);
        System.out.println("2.上一天："+last_year2);

        //取下一年
        LocalDate next_year = now.plusYears(1);
        System.out.println("下一年"+next_year);

        // 日期的修改
        LocalDate localDate = now.withYear(1998);
        System.out.println("日期修改："+localDate);

        //日期的比较
        LocalDate date = LocalDate.of(2023, 7, 22);
        System.out.println("日期的比较：之后"+now.isAfter(date));
        System.out.println("日期的比较：之前" +now.isBefore(date));
        System.out.println("日期的比较：相等"+now.isEqual(date));

        // 格式化
        DateTimeFormatter isoLocalDate = DateTimeFormatter.ISO_LOCAL_DATE;
        System.out.println(now.format(isoLocalDate));

        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyyMMdd");
        System.out.println(now.format(dateTimeFormatter));

        LocalDateTime now_date_time = LocalDateTime.now();
        System.out.println(now_date_time.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));

        //将字符串解析为日期时间类型
        LocalDate parse = LocalDate.parse("20230301", dateTimeFormatter);
        System.out.println(parse);


        // 根据 localdate 对象获取对应的日期信息
        int year = now.getYear();
        Month month = now.getMonth();
        int dayOfMonth = now.getDayOfMonth();
        DayOfWeek dayOfWeek = now.getDayOfWeek();
        System.out.println("年" + year + "\n月" + month + "\n日" + dayOfMonth + "\n周" + dayOfWeek);

    }

    @Test
    public void test02() {
        //获得指定的时间 05:22:33
        LocalTime of = LocalTime.of(5, 22, 33);
        System.out.println(of);

        //获取当前时间 18:23:36.670
        LocalTime now = LocalTime.now();
        System.out.println(now);

        //获取时间信息
        System.out.println(now.getHour());
        System.out.println(now.getMinute());
        System.out.println(now.getHour());
    }

    @Test
    public void test03() {
        //获取当前日期时间 2023-07-23T18:28:50.616
        LocalDateTime now = LocalDateTime.now();
        System.out.println(now);

        // 获取指定日期的时间 2023-12-01T03:23:11
        LocalDateTime of = LocalDateTime.of(2023
                , 12
                , 1
                , 3
                , 23
                , 11);
        System.out.println(of);
    }

    @Test
    public void test04() throws Exception{
        //获取时间戳
        Instant now = Instant.now();
        System.out.println("当前时间戳"+ now);

        // e.g 做 是运行时间统计
        Instant now1 = Instant.now();
        Thread.sleep(5000);
        Instant now2 = Instant.now();
        System.out.println("运行时间：" + (now2.getEpochSecond() - now1.getEpochSecond()) + "秒");

        //e.g 计算 日期时间的差
        /**
         *         Duration : 用来计算两个时间差
         *         Period   : 用来计算两个日期差
         */

        //计算时间差
        LocalTime now3 = LocalTime.now();
        LocalTime date = LocalTime.of(22, 44, 22);

        Duration duration = Duration.between(date, now3);
        System.out.println(duration.toDays());
        System.out.println(duration.toHours());
        System.out.println(duration.toMinutes());

        //计算日期差
        LocalDate now4 = LocalDate.now();
        LocalDate date2 = LocalDate.of(2023, 7, 20);

        Period period = Period.between(date2, now4);
        System.out.println(period.getYears());
        System.out.println(period.getMonths());
        System.out.println(period.getDays());

    }

    @Test
    public void test05(){
        /**
         *  时间矫正器  TemporalAdjuster
         */

        //e.g 找到下月第一天
        LocalDate now = LocalDate.now();
        TemporalAdjuster adjuster = (temporal)->{
            LocalDate date = (LocalDate) temporal;
            LocalDate localDate = date.plusMonths(1).withDayOfMonth(1);
            System.out.println(localDate);
            return localDate;
        };

        LocalDate next_month = now.with(adjuster);
        System.out.println(next_month);

        //可以看到主要是对 now 进行的操作 ，那么问题来了为什么要 用 TemporalAdjuster 呢
        LocalDate localDate1 = now.plusMonths(1).withDayOfMonth(1);
        System.out.println(localDate1);

        // TemporalAdjusters 通过该类的静态方法体统了大量的常用 TemporalAdjuster 操作，像之前的 例子 可以直接通过封装好的方法来使用
        TemporalAdjuster adjuster1 = TemporalAdjusters.firstDayOfNextMonth();
        System.out.println(now.with(adjuster1));

        // e.g 找到上月的第一天
        LocalDate now1 = LocalDate.now();
        LocalDate localDate = now1.minusMonths(1).withDayOfMonth(1);
        System.out.println("上月的第一天:"+localDate);

        //e.g 找到 当月的最后一天
        LocalDate now2 = LocalDate.now();
        LocalDate localDate2 = now2.plusMonths(1).withDayOfMonth(1);
        LocalDate localDate3 = localDate2.minusDays(1);
        System.out.println("当月的最后一天："+localDate3);

        //e.g 找到上月的最后一天
        LocalDate now3 = LocalDate.now();
        LocalDate localDate4 = now3.withDayOfMonth(1);
        LocalDate localDate5 = localDate4.minusDays(1);
        System.out.println("上月的最后一天"+localDate5);


    }

    @Test
    public void test06(){
        LocalDate date = LocalDate.parse("2023-02-11", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
        log.info("年：{}",date.getYear());
        log.info("月：{}",date.getMonthValue());
        log.info("日：{}",date.getDayOfMonth());
        // 上面发现取出的月份是 2 而不是 02 ，那要怎么取 02 呢
        String month = date.format(DateTimeFormatter.ofPattern("MM"));
        log.info("月份：{}",month);

        //取前一天
        LocalDate localDate = date.minusDays(1);
        System.out.println(localDate);

        //后一天
        LocalDate localDate1 = date.plusDays(1);
        System.out.println(localDate1.format(DateTimeFormatter.ofPattern("yyyyMMdd")));
    }
}