解析和格式化

---

created: 2022-07-23T14:28:10+08:00
updated: 2022-07-24T11:02:23+08:00
tags:

• DateTimeAPI
• DateTimeAPI/DateTimeFormatter

---

Parsing and Formatting

Date-Time API 中基于时间的类提供 parse() 方法来解析包含日期和时间信息的字符串。这些类还提供了 format() 方法来格式化基于时间的对象以供显示。在这两种情况下，过程是相似的：您向 DateTimeFormatter 提供一个模式来创建一个格式化程序对象。然后将此格式化程序传递给 parse() 或 format() 方法。

DateTimeFormatter 类提供了许多预定义的格式化程序，或者您可以定义自己的格式化程序。

如果在转换过程中出现问题，则 parse() 和 format() 方法会抛出异常。因此，您的解析代码应该捕获 DateTimeParseException 错误，而您的格式代码应该捕获 DateTimeException 错误。

DateTimeFormatter 类既不可变又是线程安全的；它可以（并且应该）在适当的情况下分配给静态常量。

Parsing

LocalDate 类中的单参数 parse(CharSequence) 方法使用 ISO_LOCAL_DATE 格式化程序。

example1

String in = ...;
LocalDate date = LocalDate.parse(in, DateTimeFormatter.BASIC_ISO_DATE);

example2

String input = ...;
try {
    DateTimeFormatter formatter =
                      DateTimeFormatter.ofPattern("MMM d yyyy");
    LocalDate date = LocalDate.parse(input, formatter);
    System.out.printf("%s%n", date);
}
catch (DateTimeParseException exc) {
    System.out.printf("%s is not parsable!%n", input);
    throw exc;      // Rethrow the exception.
}
// 'date' has been successfully parsed

Formatting

format(DateTimeFormatter) 方法使用指定格式将基于时间的对象转换为字符串表示形式。

example

DateTimeFormatter format = DateTimeFormatter.ofPattern("MMM d yyyy  hh:mm a");

// Leaving from San Francisco on July 20, 2013, at 7:30 p.m.
LocalDateTime leaving = LocalDateTime.of(2013, Month.JULY, 20, 19, 30);
ZoneId leavingZone = ZoneId.of("America/Los_Angeles"); 
ZonedDateTime departure = ZonedDateTime.of(leaving, leavingZone);

try {
    String out1 = departure.format(format);
    System.out.printf("LEAVING:  %s (%s)%n", out1, leavingZone);
} catch (DateTimeException exc) {
    System.out.printf("%s can't be formatted!%n", departure);
    throw exc;
}

// Flight is 10 hours and 50 minutes, or 650 minutes
ZoneId arrivingZone = ZoneId.of("Asia/Tokyo"); 
ZonedDateTime arrival = departure.withZoneSameInstant(arrivingZone)
                                 .plusMinutes(650);

try {
    String out2 = arrival.format(format);
    System.out.printf("ARRIVING: %s (%s)%n", out2, arrivingZone);
} catch (DateTimeException exc) {
    System.out.printf("%s can't be formatted!%n", arrival);
    throw exc;
}

if (arrivingZone.getRules().isDaylightSavings(arrival.toInstant())) 
    System.out.printf("  (%s daylight saving time will be in effect.)%n",
                      arrivingZone);
else
    System.out.printf("  (%s standard time will be in effect.)%n",
                      arrivingZone);

result

LEAVING:  Jul 20 2013  07:30 PM (America/Los_Angeles)
ARRIVING: Jul 21 2013  10:20 PM (Asia/Tokyo)

[[temporal包]]