Sufiyan Ghori和micha的回答都很好地解释了关于弦模式的问题。然而，以防你正在使用ISO 8601，没有任何必要应用DateTimeFormatter，因为LocalDateTime已经为它准备好了:

将LocalDateTime转换为时区ISO 8601字符串

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

从ISO8601字符串转换回LocalDateTime

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

解析日期和时间

要从字符串创建LocalDateTime对象，可以使用静态的LocalDateTime.parse()方法。它接受一个字符串和一个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);

格式化日期和时间

要从LocalDateTime对象中创建格式化字符串，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"

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。从上面格式化LocalDateTime实例的ISO_DATE_TIME将导致字符串“1986-04-08T12:30:00”。

parse()和format()方法可用于所有与日期/时间相关的对象(例如LocalDate或ZonedDateTime)

Sufiyan Ghori和micha的回答都很好地解释了关于弦模式的问题。然而，以防你正在使用ISO 8601，没有任何必要应用DateTimeFormatter，因为LocalDateTime已经为它准备好了:

将LocalDateTime转换为时区ISO 8601字符串

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

从ISO8601字符串转换回LocalDateTime

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

你也可以使用LocalDate.parse()或LocalDateTime.parse()在不提供模式的字符串上，如果字符串是ISO 8601格式。

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);

输出,

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

只有在必须处理其他日期模式时才使用DateTimeFormatter。

例如，在下面的例子中，dd MMM uuuu表示月份的日期(两位数字)，月份名称的三个字母(Jan, Feb, Mar，…)和一个四位数的年份:

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);

输出

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));

输出

2015-08-04 formats as 04 Aug 2015

(请参阅格式化和解析DateFormatter的模式的完整列表。)

  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

通用方法如下所示。它适用于:

yyyy-MM-dd HH: mm: ss。瑞士 yyyy-MM-dd HH: mm: ss。年代 yyyy-MM-dd HH: mm: ss yyyy-MM-dd HH: mm yyyy-MM-dd HH yyyy-MM-dd public static final String DATE_FORMAT_YYYY_MM_DD_HH_MM_SS_SSS = "yyyy-MM-dd HH:mm:ss.SSS"; stringtollocaldatetime (String s){ LocalDateTime返回。解析(年代,DateTimeFormatter.ofPattern (DATE_FORMAT_YYYY_MM_DD_HH_MM_SS_SSS。substring (0, s.length ()))); ｝

获取所需格式的当前UTC时间

// Current the UTC time
OffsetDateTime utc = OffsetDateTime.now(ZoneOffset.UTC);

// Get LocalDateTime
LocalDateTime localDateTime = utc.toLocalDateTime();
System.out.println("*************" + localDateTime);

// Formatted UTC time
DateTimeFormatter dTF = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
System.out.println(" formats as " + dTF.format(localDateTime));

// Get the UTC time for the current date
Date now = new Date();
LocalDateTime utcDateTimeForCurrentDateTime = Instant.ofEpochMilli(now.getTime()).atZone(ZoneId.of("UTC")).toLocalDateTime();
DateTimeFormatter dTF2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
System.out.println(" formats as " + dTF2.format(utcDateTimeForCurrentDateTime));