Parsing and Formatting解析和格式化

The temporal-based classes in the Date-Time API provide parse methods for parsing a string that contains date and time information. 日期-时间API中基于时态的类提供了用于解析包含日期和时间信息的字符串的parse方法。These classes also provide format methods for formatting temporal-based objects for display. 这些类还提供format方法，用于格式化基于时间的对象以供显示。In both cases, the process is similar: you provide a pattern to the DateTimeFormatter to create a formatter object. This formatter is then passed to the parse or format method.

The DateTimeFormatter class provides numerous predefined formatters, or you can define your own.

The parse and the format methods throw an exception if a problem occurs during the conversion process. Therefore, your parse code should catch the DateTimeParseException error and your format code should catch the DateTimeException error. For more information on exception handing, see Catching and Handling Exceptions.

The DateTimeFormatter class is both immutable and thread-safe; it can (and should) be assigned to a static constant where appropriate.

Parsing

The one-argument parse(CharSequence) method in the LocalDate class uses the ISO_LOCAL_DATE formatter. To specify a different formatter, you can use the two-argument parse(CharSequence, DateTimeFormatter) method. The following example uses the predefined BASIC_ISO_DATE formatter, which uses the format 19590709 for July 9, 1959.

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

You can also define a formatter using your own pattern. 您还可以使用自己的模式定义格式化程序。The following code, from the Parse example, creates a formatter that applies a format of "MMM d yyyy". This format specifies three characters to represent the month, one digit to represent day of the month, and four digits to represent the year. A formatter created using this pattern would recognize strings such as "Jan 3 2003" or "Mar 23 1994". However, to specify the format as "MMM dd yyyy", with two characters for day of the month, then you would have to always use two characters, padding with a zero for a one-digit date: "Jun 03 2003".但是，要将格式指定为“MMM-dd-yyy”，其中两个字符表示月份的日期，则必须始终使用两个字符，并用零填充一个数字日期：“2003年6月3日”。

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

The documentation for the DateTimeFormatter class specifies the full list of symbols that you can use to specify a pattern for formatting or parsing.

The StringConverter example on the Non-ISO Date Conversion page provides another example of a date formatter.

Formatting

The format(DateTimeFormatter) method converts a temporal-based object to a string representation using the specified format. The following code, from the Flight example, converts an instance of ZonedDateTime using the format "MMM d yyy hh:mm a". The date is defined in the same manner as was used for the previous parsing example, but this pattern also includes the hour, minutes, and a.m. and p.m. components.

ZoneId leavingZone = ...;
ZonedDateTime departure = ...;

try {
    DateTimeFormatter format = DateTimeFormatter.ofPattern("MMM d yyyy  hh:mm a");
    String out = departure.format(format);
    System.out.printf("LEAVING:  %s (%s)%n", out, leavingZone);
}
catch (DateTimeException exc) {
    System.out.printf("%s can't be formatted!%n", departure);
    throw exc;
}

The output for this example, which prints both the arrival and departure time, is as follows:该示例的输出打印到达和离开时间，如下所示：

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