ICU's replacement for
java.text.SimpleDateFormat
. Methods, fields, and other functionality specific to ICU are labeled '
[icu]'.
SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. It allows for formatting (date -> text), parsing (text -> date), and normalization.
Clients are encouraged to create a date-time formatter using DateFormat.getDateInstance(), DateFormat.getDateInstance(), or DateFormat.getDateTimeInstance() rather than explicitly constructing an instance of SimpleDateFormat. This way, the client is guaranteed to get an appropriate formatting pattern for whatever locale the program is running in. If the client needs more control, they should consider using DateFormat.getInstanceForSkeleton(). However, if the client needs something more unusual than the default patterns in the locales, he can construct a SimpleDateFormat directly and give it an appropriate pattern (or use one of the factory methods on DateFormat and modify the pattern after the fact with toPattern() and applyPattern(). For more information on using these methods, see DateFormat.
Date and Time Patterns:
Date and time formats are specified by date and time pattern strings. The full syntax for date and time patterns can be found at https://unicode.org/reports/tr35/tr35-dates.html#Date_Format_Patterns.
Within date and time pattern strings, all unquoted ASCII letters [A-Za-z] are reserved as pattern letters representing calendar fields. Some of the most commonly used pattern letters are:
Sym. No. Example Description G 1..3 AD Era - Replaced with the Era string for the current date. One to three letters for the abbreviated form, four letters for the long (wide) form, five for the narrow form. y 1..n 1996 Year. Normally the length specifies the padding, but for two letters it also specifies the maximum length. Example: Year y yy yyy yyyy yyyyy AD 1 1 01 001 0001 00001 AD 12 12 12 012 0012 00012 AD 123 123 23 123 0123 00123 AD 1234 1234 34 1234 1234 01234 AD 12345 12345 45 12345 12345 12345 Q 1..2 02 Quarter - Use one or two for the numerical quarter, three for the abbreviation, or four for the full (wide) name (five for the narrow name is not yet supported). 3 Q2 4 2nd quarter M 1..2 09 Month - Use one or two for the numerical month, three for the abbreviation, four for the full (wide) name, or five for the narrow name. With two ("MM"), the month number is zero-padded if necessary (e.g. "08"). 3 Sep 4 September 5 S d 1..2 1 Date - Day of the month. Use "d" to show the minimum number of digits, or "dd" to always show two digits (zero-padding if necessary, e.g. "08"). E 1..3 Tue Day of week - Use one through three letters for the short day, four for the full (wide) name, five for the narrow name, or six for the short name. 4 Tuesday 5 T 6 Tu a 1 AM AM or PM h 1..2 11 Hour [1-12]. When used in skeleton data or in a skeleton passed in an API for flexible data pattern generation, it should match the 12-hour-cycle format preferred by the locale (h or K); it should not match a 24-hour-cycle format (H or k). Use hh for zero padding. H 1..2 13 Hour [0-23]. When used in skeleton data or in a skeleton passed in an API for flexible data pattern generation, it should match the 24-hour-cycle format preferred by the locale (H or k); it should not match a 12-hour-cycle format (h or K). Use HH for zero padding. m 1..2 59 Minute. Use "m" to show the minimum number of digits, or "mm" to always show two digits (zero-padding if necessary, e.g. "08").. s 1..2 12 Second. Use "s" to show the minimum number of digits, or "ss" to always show two digits (zero-padding if necessary, e.g. "08"). z 1..3 PDT Time zone. The short specific non-location format. Where that is unavailable, falls back to the short localized GMT format ("O"). 4 Pacific Daylight Time The long specific non-location format. Where that is unavailable, falls back to the long localized GMT format ("OOOO"). v 1 PT Time zone. The short generic non-location format. Where that is unavailable, falls back to the generic location format ("VVVV"), then the short localized GMT format as the final fallback. 4 Pacific Time The long generic non-location format. Where that is unavailable, falls back to generic location format ("VVVV").
Any characters in the pattern that are not in the ranges of ['a'..'z'] and ['A'..'Z'] will be treated as quoted text. For instance, characters like ':', '.', ' ', '#' and '@' will appear in the resulting time text even they are not embraced within single quotes.
A pattern containing any invalid pattern letter will result in a thrown exception during formatting or parsing.
Examples Using the US Locale:
Code Sample:Format Pattern Result -------------- ------- "yyyy.MM.dd G 'at' HH:mm:ss vvvv" ->> 1996.07.10 AD at 15:08:56 Pacific Time "EEE, MMM d, ''yy" ->> Wed, July 10, '96 "h:mm a" ->> 12:08 PM "hh 'o''clock' a, zzzz" ->> 12 o'clock PM, Pacific Daylight Time "K:mm a, vvv" ->> 0:00 PM, PT "yyyyy.MMMMM.dd GGG hh:mm aaa" ->> 01996.July.10 AD 12:08 PM
SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, "PST"); pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2*60*60*1000); pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY, 2*60*60*1000);
// Format the current time. SimpleDateFormat formatter = new SimpleDateFormat ("yyyy.MM.dd G 'at' hh:mm:ss a zzz"); Date currentTime_1 = new Date(); String dateString = formatter.format(currentTime_1);
// Parse the previous string back into a Date. ParsePosition pos = new ParsePosition(0); Date currentTime_2 = formatter.parse(dateString, pos);
In the example, the time value
currentTime_2
obtained from parsing will be equal to
currentTime_1
. However, they may not be equal if the am/pm marker 'a' is left out from the format pattern while the "hour in am/pm" pattern symbol is used. This information loss can happen when formatting the time in PM.
When parsing a date string using the abbreviated year pattern ("yy"), SimpleDateFormat must interpret the abbreviated year relative to some century. It does this by adjusting dates to be within 80 years before and 20 years after the time the SimpleDateFormat instance is created. For example, using a pattern of "MM/dd/yy" and a SimpleDateFormat instance created on Jan 1, 1997, the string "01/11/12" would be interpreted as Jan 11, 2012 while the string "05/04/64" would be interpreted as May 4, 1964. During parsing, only strings consisting of exactly two digits, as defined by UCharacter.isDigit(int), will be parsed into the default century. Any other numeric string, such as a one digit string, a three or more digit string, or a two digit string that isn't all digits (for example, "-1"), is interpreted literally. So "01/02/3" or "01/02/003" are parsed, using the same pattern, as Jan 2, 3 AD. Likewise, "01/02/-3" is parsed as Jan 2, 4 BC.
If the year pattern does not have exactly two 'y' characters, the year is interpreted literally, regardless of the number of digits. So using the pattern "MM/dd/yyyy", "01/11/12" parses to Jan 11, 12 A.D.
When numeric fields abut one another directly, with no intervening delimiter characters, they constitute a run of abutting numeric fields. Such runs are parsed specially. For example, the format "HHmmss" parses the input text "123456" to 12:34:56, parses the input text "12345" to 1:23:45, and fails to parse "1234". In other words, the leftmost field of the run is flexible, while the others keep a fixed width. If the parse fails anywhere in the run, then the leftmost field is shortened by one character, and the entire run is parsed again. This is repeated until either the parse succeeds or the leftmost field is one character in length. If the parse still fails at that point, the parse of the run fails.
For time zones that have no names, use strings GMT+hours:minutes or GMT-hours:minutes.
The calendar defines what is the first day of the week, the first week of the year, whether hours are zero based or not (0 vs 12 or 24), and the time zone. There is one common decimal format to handle all the numbers; the digit count is handled programmatically according to the pattern.
SynchronizationDate formats are not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.
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