JAVA8新特性随笔

Posted 2020-11-21 lqq7456

Instant：瞬时实例
LocalDate：本地日期，不包含具体时间。例如：2014-01-14可以用来记录生日、纪念日、加盟日等。
LocalTime：本地时间，不包含日期
LocalDateTime：组合了日期和时间，但不包含时差和时区信息
ZonedDateTime：最完整的日期时间，包含时区和相对UTC或格林威治的时差

日期类和时间类

1. ==获取当前时间==：LocalDateTime.now();
2. ==日期格式化==:：LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss a"));
3. ==获取时间戳==：Instant.now()
   （Date.from(Instant)将Instant转换成java.util.Date，Date.toInstant()则是将Date类转换成Instant类。）
4. ==LocalDateTime转String==: LocalDateTime.parse(str,dateTimeFormatter); ==String转LocalDateTime==: localDateTime.format(dateTimeFormatter);
5. ==Date转LocalDateTime==：LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
6. ==LocalDateTime转Date==：Date date = Date.from(LocalDateTime.now().atZone(ZoneId.systemDefault()).toInstant());
7. ==前端传过来的日期字符串怎么转换并放到数据库==

        LocalDate localDate = LocalDate.now();
        System.out.println("LocalDate.now():"+localDate);
        System.out.println("localDate.getYear():"+localDate.getYear());
        System.out.println("localDate.getMonth():"+localDate.getMonth());
        System.out.println("localDate.getMonthValue():"+localDate.getMonthValue());
        System.out.println("localDate.getDayOfMonth():"+localDate.getDayOfMonth());
        System.out.println("localDate.getDayOfWeek():"+localDate.getDayOfWeek());
        System.out.println("localDate.getDayOfWeek().getValue():"+localDate.getDayOfWeek().getValue());

        LocalTime localTime = LocalTime.now();
        System.out.println("当前时间LocalTime.now(): " + localTime);
        System.out.println("当前时间+1小时 localTime.plusHours(1): " + localTime.plusHours(1));

        Clock clock = Clock.systemUTC();
        Clock clock2 = Clock.systemDefaultZone();
        System.out.println("Clock : " + clock.millis());
        System.out.println("clock2 : " + clock2.millis());
        System.out.println("=== 获取当前的时间戳 ===============================================");
        Instant timestamp = Instant.now();
        System.out.println("获取当前的时间戳: "+timestamp);
        System.out.println("=== 格式化日期 ===============================================");
        DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss a");
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println(" LocalDateTime.now(): "+localDateTime);
        System.out.println(" 格式化后的日期："+localDateTime.format(format));

        System.out.println("=== 检查生日等周期性事件 ===============================================");
        LocalDate dateOfBirth = LocalDate.of(2019, 7, 25);
        MonthDay birthday = MonthDay.of(dateOfBirth.getMonth(), dateOfBirth.getDayOfMonth());
        MonthDay currentMonthDay = MonthDay.from(localDate);

        if(currentMonthDay.equals(birthday)){
            System.out.println(" Many Many happy returns of the day !!");
        }else{
            System.out.println(" Sorry, today is not your birthday");
        }