LocalDateTime

JDK8新特性里提供了3个时间类：LocalDate、LocalTime、LocalDateTime

SimpleDateFormat是线程不安全的、DateTimeFormatter是线程安全的

具体用法

public static void main(String[] args) {

        /**
         * LocalDate：仅含年月日
         * LocalTime：仅含时分秒
         * LocalDateTime：含年月日时分秒
         */

        //Instant: 返回Java纪元(epoch)，即1970-01-01T00：00：00Z（1970年1月1日00:00 GMT）以来的时间点
        //getEpochSecond()返回自纪元以来经过的秒数。
        //getNano()方法返回自上一秒开始以来的纳秒数。
        Instant now = Instant.now();
        System.out.println(now.getEpochSecond() + "." + now.getNano());
        System.out.println(System.currentTimeMillis());

        System.out.println("----------------Clock------------------");
        //Clock : 时钟
        Clock clock = Clock.systemDefaultZone();
        System.out.println("当前系统时区：" + clock);
        System.out.println("当前时间毫秒：" + clock.millis());
        Date from = Date.from(clock.instant());
        System.out.println("当前时间(Date)：" + from);

        System.out.println("----------------Timezones------------------");
        //Timezones : 时区
        ZoneId zoneId = ZoneId.of("Asia/Shanghai");
        System.out.println("上海时区：" + zoneId);
        System.out.println("上海时区规则：" + zoneId.getRules());

        System.out.println("----------------LocalDate------------------");
        //LocalDate: 只包含日期，不包含时间
        LocalDate nowDate = LocalDate.now();
        System.out.println("今天的日期：" + nowDate);
        System.out.println("今天是一年中的第多少周：" + nowDate.getDayOfMonth());
        System.out.println("今天是周几(英文)：" + nowDate.getDayOfWeek());
        System.out.println("今天是一年中的第多少天：" + nowDate.getDayOfYear());
        System.out.println("今天的月份(英文)：" + nowDate.getMonth());
        System.out.println("今天的月份(数字)：" + nowDate.getMonthValue());
        System.out.println("今天的年份(数字)：" + nowDate.getYear());
        System.out.println("指定月份：" + nowDate.withMonth(11));
        LocalDate tomorrow = nowDate.plus(1, ChronoUnit.DAYS);
        LocalDate tomorrow1 = nowDate.plusDays(1);
        System.out.println("明天的日期: " + tomorrow);
        System.out.println("明天的日期: " + tomorrow1);
        System.out.println("昨天的日期: " + nowDate.minusDays(1));
        System.out.println("20年前的今天是: " + LocalDate.now().minus(2, ChronoUnit.DECADES));
        System.out.println("定义的日期是: " + LocalDate.of(2020, Month.MARCH, 12));
        System.out.println("字符转换日期：" + LocalDate.parse("2020-02-02"));
        System.out.println("判断日期先后：" + nowDate.isAfter(LocalDate.parse("2020-02-02")));

        System.out.println("----------------LocalTime------------------");
        //LocalTime: 只包含时间，不包含日期
        LocalTime nowTime = LocalTime.now();
        System.out.println("当前系统默认时区时间：" + nowTime);
        System.out.println("当前系统默认时区时间(不包含毫秒数)：" + nowTime.withNano(0));
        LocalTime losTime = LocalTime.now(ZoneId.of("America/Los_Angeles"));
        System.out.println("洛杉矶时区当前时间：" + losTime);
        System.out.println("时区转换：" + losTime.adjustInto(nowTime));
        System.out.println("当前小时：" + nowTime.getHour());
        System.out.println("当前分钟：" + nowTime.getMinute());
        System.out.println("当前秒：" + nowTime.getSecond());
        System.out.println("指定小时: " + nowTime.withHour(12));
        System.out.println("指定毫秒值" + nowTime.withNano(12345));
        System.out.println("两个时间时间差:" + ChronoUnit.HOURS.between(losTime, nowTime));
        System.out.println("一小时前：" + nowTime.minus(1, ChronoUnit.HOURS));
        System.out.println("一小时后：" + nowTime.plusHours(1));
        System.out.println("定义的时间是：" + LocalTime.of(13, 59, 59));
        System.out.println("字符转换时间：" + LocalTime.parse("13:59:59"));
        System.out.println("判断时间先后：" + nowTime.isAfter(LocalTime.parse("13:59:59")));

        System.out.println("----------------LocalDateTime------------------");
        //LocalDateTime: 包含时间，日期
        LocalDateTime nowDateTime = LocalDateTime.now();
        System.out.println("当前时间：" + nowDateTime);
        System.out.println("当前时间戳(秒)：" + nowDateTime.toEpochSecond(ZoneOffset.of("+8")));
        System.out.println("当前时间戳(毫秒)：" + nowDateTime.toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println("当前年份：" + nowDateTime.getYear());
        System.out.println("当前分钟：" + nowDateTime.getMinute());
        System.out.println("定义的时间是：" + LocalDateTime.of(2020, 2, 28, 12, 59, 59));
        System.out.println("2年后 : " + nowDateTime.plusYears(2L));
        System.out.println("3天前 : " + nowDateTime.minusDays(3L));
        System.out.println("指定小时: " + nowDateTime.withHour(12));
        System.out.println("字符转换时间：" + LocalDateTime.parse("2020-02-27 20:59:59", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
        System.out.println("Date转换：" + new Date().toInstant().atOffset(ZoneOffset.of("+8")).toLocalDateTime());
        System.out.println("转换Date：" + Date.from(nowDateTime.toInstant(ZoneOffset.of("+8"))));
        System.out.println("判断时间先后：" + nowDateTime.isAfter(LocalDateTime.of(2020, 2, 28, 12, 59, 59)));

        System.out.println("----------------Formatter------------------");
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        DateTimeFormatter formatter1 = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("HH:mm:ss");
        System.out.println(formatter.format(nowDateTime));
        System.out.println(formatter1.format(nowDate));
        System.out.println(formatter2.format(nowTime));
    }
}