SimpleDateFormat格式化数据-付官方文档

compact1, compact2, compact3

java.text

Class SimpleDateFormat

• 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 (context sensitive)	Month	July; Jul; 07
  L	Month in year (standalone form)	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 by Character.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 formis 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.
    
    • Letter M produces context-sensitive month names, such as the embedded form of names. If a DateFormatSymbols has been set explicitly with constructor SimpleDateFormat(String, DateFormatSymbols) or method setDateFormatSymbols(DateFormatSymbols), the month names given by the DateFormatSymbols are used.
    • Letter L produces the standalone form of month names.
    
    
  • 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.

  See Also:

  Java Tutorial,  Calendar,  TimeZone,  DateFormat,  DateFormatSymbols,  Serialized Form

看了官方文档描述，大概意思就是

1、支持从日期到文本及文本到日期的转换，提供默认的格式化方法及修改方式；

2、A到Z，a到z为预留字段，表示日期的格式化属性，如果作为文本需要通过单引号避免被解释；

3、不支持同步；

4、日期文本中包含中文字符时直接作为pattern的一部分进行格式化

常用规则：

public class FormatDateTime {

    public static void main(String[] args) {
        SimpleDateFormat myFmt=new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒");
        SimpleDateFormat myFmt1=new SimpleDateFormat("yy/MM/dd HH:mm"); 
        SimpleDateFormat myFmt2=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//等价于now.toLocaleString()
        SimpleDateFormat myFmt3=new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒 E ");
        SimpleDateFormat myFmt4=new SimpleDateFormat(
                "一年中的第 D 天 一年中第w个星期 一月中第W个星期 在一天中k时 z时区");
        Date now=new Date();
        System.out.println(myFmt.format(now));
        System.out.println(myFmt1.format(now));
        System.out.println(myFmt2.format(now));
        System.out.println(myFmt3.format(now));
        System.out.println(myFmt4.format(now));
        System.out.println(now.toGMTString());
        System.out.println(now.toLocaleString());
        System.out.println(now.toString());
    }    
    
}

效果：
2004年12月16日 17时24分27秒
04/12/16 17:24
2004-12-16 17:24:27
2004年12月16日 17时24分27秒 星期四 
一年中的第 351 天 一年中第51个星期 一月中第3个星期 在一天中17时 CST时区
16 Dec 2004 09:24:27 GMT
2004-12-16 17:24:27
Thu Dec 16 17:24:27 CST 2004

下面是个JavaBean:
public class FormatDateTime {
    
    public static String toLongDateString(Date dt){
        SimpleDateFormat myFmt=new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒 E ");        
        return myFmt.format(dt);
    }
    
    public static String toShortDateString(Date dt){
        SimpleDateFormat myFmt=new SimpleDateFormat("yy年MM月dd日 HH时mm分");        
        return myFmt.format(dt);
    }    
    
    public static String toLongTimeString(Date dt){
        SimpleDateFormat myFmt=new SimpleDateFormat("HH mm ss SSSS");        
        return myFmt.format(dt);
    }
    public static String toShortTimeString(Date dt){
        SimpleDateFormat myFmt=new SimpleDateFormat("yy/MM/dd HH:mm");        
        return myFmt.format(dt);
    }
    
    public static void main(String[] args) {

        Date now=new Date();

        System.out.println(FormatDateTime.toLongDateString(now));
        System.out.println(FormatDateTime.toShortDateString(now));
        System.out.println(FormatDateTime.toLongTimeString(now));
        System.out.println(FormatDateTime.toShortTimeString(now));
    }    
    
}
调用的main 测试结果：
2004年12月16日 17时38分26秒 星期四 
04年12月16日 17时38分
17 38 26 0965

一些有些变态的用法：

public static void main(String[] args) throws Exception {
Date date = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); //不支持第一种字符串格式化；
SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-ddhh:mm:ss"); //建议采用该方式，可同时支持格式1、2解析
SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd\\s*hh:mm:ss"); //不支持正则方式
SimpleDateFormat sdf3 = new SimpleDateFormat("yyyyMMddhhmmss");
SimpleDateFormat sdf4 = new SimpleDateFormat("yyyyMMddhhmmssZ");
String dateStr = "2018-01-0211:29:19";
String dateStr1 = "2018-01-02 11:29:19";
String dateStr2 = "20180102112919";

// System.out.println(sdf.parse(dateStr)); //Error,Unparseable date
// System.out.println(sdf.parse(dateStr1)); //Success
// System.out.println(sdf.format(sdf1.parse(dateStr))); //success
// System.out.println(sdf.format(sdf1.parse(dateStr1))); //success
//
// System.out.println(sdf2.format(dateStr)); //error Cannot format given Object as a Date
// System.out.println(sdf2.format(dateStr1)); //error Cannot format given Object as a Date

System.out.println(sdf3.parse(dateStr2)); //Tue Jan 02 11:29:19 CST 2018
System.out.println(sdf4.format(date)); //20180103031436+0800
}