java.text Class SimpleDateFormat 格式详细介绍

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概述

java.lang.Object
- java.text.Format
- - java.text.DateFormat
  - - java.text.SimpleDateFormat

All Implemented Interfaces:

Serializable, Cloneable

public class SimpleDateFormat
extends DateFormat

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.

SimpleDateFormat allows you to start by choosing any user-defined patterns for date-time formatting. However, you are encouraged to create a date-time formatter with either getTimeInstance, getDateInstance, or getDateTimeInstance in DateFormat. Each of these class methods can return a date/time formatter initialized with a default format pattern. You may modify the format pattern using the applyPattern methods as desired. 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. Within date and time pattern strings, unquoted letters from 'A' to 'Z' and from 'a' to 'z' are interpreted as pattern letters representing the components of a date or time string. Text can be quoted using single quotes (') to avoid interpretation. "''" represents a single quote. All other characters are not interpreted; they're simply copied into the output string during formatting or matched against the input string during parsing.

The following pattern letters are defined (all other characters from 'A' to 'Z' and from 'a' to 'z' are reserved):

Letter Date or Time Component Presentation Examples
G Era designator Text AD
y Year Year 1996; 96
Y Week year Year 2009; 09
M Month in year Month July; Jul; 07
w Week in year Number 27
W Week in month Number 2
D Day in year Number 189
d Day in month Number 10
F Day of week in month Number 2
E Day name in week Text Tuesday; Tue
u Day number of week (1 = Monday, ..., 7 = Sunday) Number 1
a Am/pm marker Text PM
H Hour in day (0-23) Number 0
k Hour in day (1-24) Number 24
K Hour in am/pm (0-11) Number 0
h Hour in am/pm (1-12) Number 12
m Minute in hour Number 30
s Second in minute Number 55
S Millisecond Number 978
z Time zone General time zone Pacific Standard Time; PST; GMT-08:00
Z Time zone RFC 822 time zone -0800
X Time zone ISO 8601 time zone -08; -0800; -08:00

Pattern letters are usually repeated, as their number determines the exact presentation:

Text: For formatting, if the number of pattern letters is 4 or more, the full form is used; otherwise a short or abbreviated form is used if available. For parsing, both forms are accepted, independent of the number of pattern letters.
Number: For formatting, the number of pattern letters is the minimum number of digits, and shorter numbers are zero-padded to this amount. For parsing, the number of pattern letters is ignored unless it's needed to separate two adjacent fields.
Year: If the formatter's Calendar is the Gregorian calendar, the following rules are applied.
- For formatting, if the number of pattern letters is 2, the year is truncated to 2 digits; otherwise it is interpreted as a number.
- For parsing, if the number of pattern letters is more than 2, 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.
- For parsing with the abbreviated year pattern ("y" or "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 byCharacter.isDigit(char), 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.
Otherwise, calendar system specific forms are applied. For both formatting and parsing, if the number of pattern letters is 4 or more, a calendar specific long form is used. Otherwise, a calendar specific short or abbreviated form is used.

If week year 'Y' is specified and the calendar doesn't support any week years, the calendar year ('y') is used instead. The support of week years can be tested with a call to getCalendar().isWeekDateSupported().
Month: If the number of pattern letters is 3 or more, the month is interpreted as text; otherwise, it is interpreted as a number.
General time zone: Time zones are interpreted as text if they have names. For time zones representing a GMT offset value, the following syntax is used:
```
GMTOffsetTimeZone:
GMT Sign Hours : Minutes
Sign: one of
+ -
Hours:
Digit
Digit Digit
Minutes:
Digit Digit
Digit: one of
0 1 2 3 4 5 6 7 8 9
```
Hours must be between 0 and 23, and Minutes must be between 00 and 59. The format is locale independent and digits must be taken from the Basic Latin block of the Unicode standard.
For parsing, RFC 822 time zones are also accepted.
RFC 822 time zone: For formatting, the RFC 822 4-digit time zone format is used:
```
RFC822TimeZone:
Sign TwoDigitHours Minutes
TwoDigitHours:
Digit Digit
```
TwoDigitHours must be between 00 and 23. Other definitions are as for general time zones.
For parsing, general time zones are also accepted.
ISO 8601 Time zone: The number of pattern letters designates the format for both formatting and parsing as follows:
```
ISO8601TimeZone:
OneLetterISO8601TimeZone
TwoLetterISO8601TimeZone
ThreeLetterISO8601TimeZone
OneLetterISO8601TimeZone:
Sign TwoDigitHours
Z
TwoLetterISO8601TimeZone:
Sign TwoDigitHours Minutes
Z
ThreeLetterISO8601TimeZone:
Sign TwoDigitHours : Minutes
Z
```
Other definitions are as for general time zones or RFC 822 time zones.
For formatting, if the offset value from GMT is 0, "Z" is produced. If the number of pattern letters is 1, any fraction of an hour is ignored. For example, if the pattern is "X" and the time zone is "GMT+05:30", "+05" is produced.

For parsing, "Z" is parsed as the UTC time zone designator. General time zones are not accepted.

If the number of pattern letters is 4 or more, IllegalArgumentException is thrown when constructing a SimpleDateFormat or applying a pattern.

SimpleDateFormat also supports localized date and time pattern strings. In these strings, the pattern letters described above may be replaced with other, locale dependent, pattern letters. SimpleDateFormat does not deal with the localization of text other than the pattern letters; that's up to the client of the class.

Examples

The following examples show how date and time patterns are interpreted in the U.S. locale. The given date and time are 2001-07-04 12:08:56 local time in the U.S. Pacific Time time zone.

Date and Time Pattern Result
"yyyy.MM.dd G 'at' HH:mm:ss z" 2001.07.04 AD at 12:08:56 PDT
"EEE, MMM d, ''yy" Wed, Jul 4, '01
"h:mm a" 12:08 PM
"hh 'o''clock' a, zzzz" 12 o'clock PM, Pacific Daylight Time
"K:mm a, z" 0:08 PM, PDT
"yyyyy.MMMMM.dd GGG hh:mm aaa" 02001.July.04 AD 12:08 PM
"EEE, d MMM yyyy HH:mm:ss Z" Wed, 4 Jul 2001 12:08:56 -0700
"yyMMddHHmmssZ" 010704120856-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSZ" 2001-07-04T12:08:56.235-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSXXX" 2001-07-04T12:08:56.235-07:00
"YYYY-'W'ww-u" 2001-W27-3

Synchronization

Date 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.

Constructor Summary

Constructors
Constructor and Description
`SimpleDateFormat()` Constructs a `SimpleDateFormat` using the default pattern and date format symbols for the default locale.
`SimpleDateFormat(String pattern)` Constructs a `SimpleDateFormat` using the given pattern and the default date format symbols for the default locale.
`SimpleDateFormat(String pattern, DateFormatSymbols formatSymbols)` Constructs a `SimpleDateFormat` using the given pattern and date format symbols.
`SimpleDateFormat(String pattern, Locale locale)` Constructs a `SimpleDateFormat` using the given pattern and the default date format symbols for the given locale.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`applyLocalizedPattern(String pattern)` Applies the given localized pattern string to this date format.
`void`	`applyPattern(String pattern)` Applies the given pattern string to this date format.
`Object`	`clone()` Creates a copy of this `SimpleDateFormat`.
`boolean`	`equals(Object obj)` Compares the given object with this `SimpleDateFormat` for equality.
`StringBuffer`	`format(Date date, StringBuffer toAppendTo, FieldPosition pos)` Formats the given `Date` into a date/time string and appends the result to the given `StringBuffer`.
`AttributedCharacterIterator`	`formatToCharacterIterator(Object obj)` Formats an Object producing an `AttributedCharacterIterator`.
`Date`	`get2DigitYearStart()` Returns the beginning date of the 100-year period 2-digit years are interpreted as being within.
`DateFormatSymbols`	`getDateFormatSymbols()` Gets a copy of the date and time format symbols of this date format.
`int`	`hashCode()` Returns the hash code value for this `SimpleDateFormat` object.
`Date`	`parse(String text, ParsePosition pos)` Parses text from a string to produce a `Date`.
`void`	`set2DigitYearStart(Date startDate)` Sets the 100-year period 2-digit years will be interpreted as being in to begin on the date the user specifies.
`void`	`setDateFormatSymbols(DateFormatSymbols newFormatSymbols)` Sets the date and time format symbols of this date format.
`String`	`toLocalizedPattern()` Returns a localized pattern string describing this date format.
`String`	`toPattern()` Returns a pattern string describing this date format.

Methods inherited from class java.text.DateFormat
format, format, getAvailableLocales, getCalendar, getDateInstance, getDateInstance, getDateInstance, getDateTimeInstance, getDateTimeInstance, getDateTimeInstance, getInstance, getNumberFormat, getTimeInstance, getTimeInstance, getTimeInstance, getTimeZone,isLenient, parse, parseObject, setCalendar, setLenient, setNumberFormat, setTimeZone

Methods inherited from class java.text.Format
format, parseObject

Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - SimpleDateFormat
```
public SimpleDateFormat()
```
    Constructs a SimpleDateFormat using the default pattern and date format symbols for the default locale. Note: This constructor may not support all locales. For full coverage, use the factory methods in the DateFormat class.
  - SimpleDateFormat
```
public SimpleDateFormat(String pattern)
```
    Constructs a SimpleDateFormat using the given pattern and the default date format symbols for the default locale. Note: This constructor may not support all locales. For full coverage, use the factory methods in the DateFormat class.
    
    Parameters:
    pattern - the pattern describing the date and time format
    Throws:
    NullPointerException - if the given pattern is null
    
    IllegalArgumentException - if the given pattern is invalid
  - SimpleDateFormat
```
public SimpleDateFormat(String pattern,
Locale locale)
```
    Constructs a SimpleDateFormat using the given pattern and the default date format symbols for the given locale. Note: This constructor may not support all locales. For full coverage, use the factory methods in the DateFormat class.
    
    Parameters:
    pattern - the pattern describing the date and time format
    
    locale - the locale whose date format symbols should be used
    Throws:
    NullPointerException - if the given pattern or locale is null
    
    IllegalArgumentException - if the given pattern is invalid
  - SimpleDateFormat
```
public SimpleDateFormat(String pattern,
DateFormatSymbols formatSymbols)
```
    Constructs a SimpleDateFormat using the given pattern and date format symbols.
    
    Parameters:
    pattern - the pattern describing the date and time format
    
    formatSymbols - the date format symbols to be used for formatting
    Throws:
    NullPointerException - if the given pattern or formatSymbols is null
    
    IllegalArgumentException - if the given pattern is invalid
- Method Detail
  - set2DigitYearStart
```
public void set2DigitYearStart(Date startDate)
```
    Sets the 100-year period 2-digit years will be interpreted as being in to begin on the date the user specifies.
    
    Parameters:
    startDate - During parsing, two digit years will be placed in the range startDate to startDate + 100 years.
    Since:
    1.2
    See Also:
    get2DigitYearStart()
  - get2DigitYearStart
```
public Date get2DigitYearStart()
```
    Returns the beginning date of the 100-year period 2-digit years are interpreted as being within.
    
    Returns:
    the start of the 100-year period into which two digit years are parsed
    Since:
    1.2
    See Also:
    set2DigitYearStart(java.util.Date)
  - format
```
public StringBuffer format(Date date,
StringBuffer toAppendTo,
FieldPosition pos)
```
    Formats the given Date into a date/time string and appends the result to the given StringBuffer.
    
    Specified by:
    format in class DateFormat
    Parameters:
    date - the date-time value to be formatted into a date-time string.
    
    toAppendTo - where the new date-time text is to be appended.
    
    pos - the formatting position. On input: an alignment field, if desired. On output: the offsets of the alignment field.
    Returns:
    the formatted date-time string.
    Throws:
    NullPointerException - if the given date is null.
  - formatToCharacterIterator
```
public AttributedCharacterIterator formatToCharacterIterator(Object obj)
```
    Formats an Object producing an AttributedCharacterIterator. You can use the returned AttributedCharacterIterator to build the resulting String, as well as to determine information about the resulting String.
    Each attribute key of the AttributedCharacterIterator will be of type DateFormat.Field, with the corresponding attribute value being the same as the attribute key.
    
    Overrides:
    formatToCharacterIterator in class Format
    Parameters:
    obj - The object to format
    Returns:
    AttributedCharacterIterator describing the formatted value.
    Throws:
    NullPointerException - if obj is null.
    
    IllegalArgumentException - if the Format cannot format the given object, or if the Format's pattern string is invalid.
    Since:
    1.4
  - parse
```
public Date parse(String text,
ParsePosition pos)
```
    Parses text from a string to produce a Date.
    The method attempts to parse text starting at the index given by pos. If parsing succeeds, then the index of pos is updated to the index after the last character used (parsing does not necessarily use all characters up to the end of the string), and the parsed date is returned. The updated pos can be used to indicate the starting point for the next call to this method. If an error occurs, then the index of pos is not changed, the error index of pos is set to the index of the character where the error occurred, and null is returned.
    
    This parsing operation uses the calendar to produce a Date. All of the calendar's date-time fields are cleared before parsing, and the calendar's default values of the date-time fields are used for any missing date-time information. For example, the year value of the parsed Date is 1970 withGregorianCalendar if no year value is given from the parsing operation. The TimeZone value may be overwritten, depending on the given pattern and the time zone value in text. Any TimeZone value that has previously been set by a call to setTimeZone may need to be restored for further operations.
    
    Specified by:
    parse in class DateFormat
    Parameters:
    text - A String, part of which should be parsed.
    
    pos - A ParsePosition object with index and error index information as described above.
    Returns:
    A Date parsed from the string. In case of error, returns null.
    Throws:
    NullPointerException - if text or pos is null.
  - toPattern
```
public String toPattern()
```
    Returns a pattern string describing this date format.
    
    Returns:
    a pattern string describing this date format.
  - toLocalizedPattern
```
public String toLocalizedPattern()
```
    Returns a localized pattern string describing this date format.
    
    Returns:
    a localized pattern string describing this date format.
  - applyPattern
```
public void applyPattern(String pattern)
```
    Applies the given pattern string to this date format.
    
    Parameters:
    pattern - the new date and time pattern for this date format
    Throws:
    NullPointerException - if the given pattern is null
    
    IllegalArgumentException - if the given pattern is invalid
  - applyLocalizedPattern
```
public void applyLocalizedPattern(String pattern)
```
    Applies the given localized pattern string to this date format.
    
    Parameters:
    pattern - a String to be mapped to the new date and time format pattern for this format
    Throws:
    NullPointerException - if the given pattern is null
    
    IllegalArgumentException - if the given pattern is invalid
  - getDateFormatSymbols
```
public DateFormatSymbols getDateFormatSymbols()
```
    Gets a copy of the date and time format symbols of this date format.
    
    Returns:
    the date and time format symbols of this date format
    See Also:
    setDateFormatSymbols(java.text.DateFormatSymbols)
  - setDateFormatSymbols
```
public void setDateFormatSymbols(DateFormatSymbols newFormatSymbols)
```
    Sets the date and time format symbols of this date format.
    
    Parameters:
    newFormatSymbols - the new date and time format symbols
    Throws:
    NullPointerException - if the given newFormatSymbols is null
    See Also:
    getDateFormatSymbols()
  - clone
```
public Object clone()
```
    Creates a copy of this SimpleDateFormat. This also clones the format's date format symbols.
    
    Overrides:
    clone in class DateFormat
    Returns:
    a clone of this SimpleDateFormat
    See Also:
    Cloneable
  - hashCode
```
public int hashCode()
```
    Returns the hash code value for this SimpleDateFormat object.
    
    Overrides:
    hashCode in class DateFormat
    Returns:
    the hash code value for this SimpleDateFormat object.
    See Also:
    Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)
  - equals
```
public boolean equals(Object obj)
```
    Compares the given object with this SimpleDateFormat for equality.
    
    Overrides:
    equals in class DateFormat
    Parameters:
    obj - the reference object with which to compare.
    Returns:
    true if the given object is equal to this SimpleDateFormat
    See Also:
    Object.hashCode(), HashMap

原文来自

http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html

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发布日期：2023-11-26 21:25:05
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java.text Class SimpleDateFormat 格式详细介绍

概述