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如何使用LocalDateTime解析/格式化日期? (Java 8)

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Java 8添加了一个新的java.time API,用于处理日期和时间(JSR 310) .

我将日期和时间作为字符串(例如 "2014-04-08 12:30" ) . 如何从给定的字符串中获取LocalDateTime实例?

使用完 LocalDateTime 对象后:如何将 LocalDateTime 实例转换回具有上述格式的字符串?

3 回答

  • 429

    Parsing date and time

    要从字符串创建 LocalDateTime 对象,可以使用静态LocalDateTime.parse()方法 . 它需要一个字符串和一个DateTimeFormatter作为参数 . DateTimeFormatter 用于指定日期/时间模式 .

    String str = "1986-04-08 12:30";
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
    LocalDateTime dateTime = LocalDateTime.parse(str, formatter);
    

    Formatting date and time

    要从 LocalDateTime 对象创建格式化字符串,可以使用 format() 方法 .

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
    LocalDateTime dateTime = LocalDateTime.of(1986, Month.APRIL, 8, 12, 30);
    String formattedDateTime = dateTime.format(formatter); // "1986-04-08 12:30"
    

    请注意,在 DateTimeFormatter 中有一些常用的日期/时间格式预定义为常量 . 例如:使用 DateTimeFormatter.ISO_DATE_TIME 从上面格式化 LocalDateTime 实例将导致字符串 "1986-04-08T12:30:00" .

    parse()format() 方法适用于所有与日期/时间相关的对象(例如 LocalDateZonedDateTime

  • 28

    如果 StringISO-8601 format中,您还可以在 String 上使用 LocalDate.parse()LocalDateTime.parse() 而不为其提供模式 .

    例如,

    String strDate = "2015-08-04";
    LocalDate aLD = LocalDate.parse(strDate);
    System.out.println("Date: " + aLD);
    
    String strDatewithTime = "2015-08-04T10:11:30";
    LocalDateTime aLDT = LocalDateTime.parse(strDatewithTime);
    System.out.println("Date with Time: " + aLDT);
    

    Output

    Date: 2015-08-04
    Date with Time: 2015-08-04T10:11:30
    

    并且仅当您必须处理其他日期模式时才使用 DateTimeFormatter ,例如, dd MMM uuuu 表示月中的某一天(两位数),该月份名称的三个字母(Jan,Feb,Mar,...),以及一个四位数的年份:

    DateTimeFormatter dTF = DateTimeFormatter.ofPattern("dd MMM uuuu");
    String anotherDate = "04 Aug 2015";
    LocalDate lds = LocalDate.parse(anotherDate, dTF);
    System.out.println(anotherDate + " parses to " + lds);
    

    Output

    04 Aug 2015 parses to 2015-08-04
    

    还记得 DateTimeFormatter 对象是双向的;它既可以解析输入也可以格式化输出 .

    String strDate = "2015-08-04";
    LocalDate aLD = LocalDate.parse(strDate);
    DateTimeFormatter dTF = DateTimeFormatter.ofPattern("dd MMM uuuu");
    System.out.println(aLD + " formats as " + dTF.format(aLD));
    

    Output

    2015-08-04 formats as 04 Aug 2015
    

    (见完整list of Patterns for Formatting and Parsing DateFormatter

    Symbol  Meaning                     Presentation      Examples
      ------  -------                     ------------      -------
       G       era                         text              AD; Anno Domini; A
       u       year                        year              2004; 04
       y       year-of-era                 year              2004; 04
       D       day-of-year                 number            189
       M/L     month-of-year               number/text       7; 07; Jul; July; J
       d       day-of-month                number            10
    
       Q/q     quarter-of-year             number/text       3; 03; Q3; 3rd quarter
       Y       week-based-year             year              1996; 96
       w       week-of-week-based-year     number            27
       W       week-of-month               number            4
       E       day-of-week                 text              Tue; Tuesday; T
       e/c     localized day-of-week       number/text       2; 02; Tue; Tuesday; T
       F       week-of-month               number            3
    
       a       am-pm-of-day                text              PM
       h       clock-hour-of-am-pm (1-12)  number            12
       K       hour-of-am-pm (0-11)        number            0
       k       clock-hour-of-am-pm (1-24)  number            0
    
       H       hour-of-day (0-23)          number            0
       m       minute-of-hour              number            30
       s       second-of-minute            number            55
       S       fraction-of-second          fraction          978
       A       milli-of-day                number            1234
       n       nano-of-second              number            987654321
       N       nano-of-day                 number            1234000000
    
       V       time-zone ID                zone-id           America/Los_Angeles; Z; -08:30
       z       time-zone name              zone-name         Pacific Standard Time; PST
       O       localized zone-offset       offset-O          GMT+8; GMT+08:00; UTC-08:00;
       X       zone-offset 'Z' for zero    offset-X          Z; -08; -0830; -08:30; -083015; -08:30:15;
       x       zone-offset                 offset-x          +0000; -08; -0830; -08:30; -083015; -08:30:15;
       Z       zone-offset                 offset-Z          +0000; -0800; -08:00;
    
       p       pad next                    pad modifier      1
    
       '       escape for text             delimiter
       ''      single quote                literal           '
       [       optional section start
       ]       optional section end
       #       reserved for future use
       {       reserved for future use
       }       reserved for future use
    
  • 118

    上面的两个答案都很好地解释了关于字符串模式的问题但是,如果您正在使用ISO 8601,则无需应用 DateTimeFormatter ,因为LocalDateTime已经为它准备好了:

    Convert LocalDateTime to Time Zone ISO8601 String

    LocalDateTime ldt = LocalDateTime.now(); 
    ZonedDateTime zdt = ldt.atZone(ZoneOffset.UTC); //you might use a different zone
    String iso8601 = zdt.toString();
    

    Convert from ISO8601 String back to a LocalDateTime

    String iso8601 = "2016-02-14T18:32:04.150Z";
    ZonedDateTime zdt = ZonedDateTime.parse(iso8601);
    LocalDateTime ldt = zdt.toLocalDateTime();
    

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