Analysis of Java SimpleDateFormat

 

1 Introduction

 

article begins, let's look at a short code, this code can run it?

 

  

 1 package simpledate; 
 2  
 3 import java.text.ParseException; 
 4 import java.text.SimpleDateFormat; 
 5 import java.util.Date; 
 6  
 7 public class Format { 
 8      
 9     public static void main(String[] args) throws ParseException { 
10         String date = "2012-12-12"; 
11         SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); 
12         Date end = simpleDateFormat.parse(date.trim()); 
13          
14     } 
15  
16 }

 

 

answer is no, this code will be reported java.text.ParseException error, which I encountered in the project yesterday a small problem, let us read the following explanations come back to see why there is this error.

 

1.1 Introduction

 

 

SimpleDateFormat inherited DateFormat, essentially it is a date through a pattern to control the output style tools.

 

1.2 Constructor

 

its constructor method has four, generally we use the first two on it.

 

 

If you do not want the time specified in the constructor class style, you can also select the first constructor, but you must use it before using the specified style.

 

  

1 public static void main(String[] args) throws ParseException {         
2     SimpleDateFormat format5 = new SimpleDateFormat(); 
3     Date date = new Date(); 
4     format5.applyPattern("yyyy-MM-dd"); 
5     System.out.println(format5.format(date));     
6 }

 

 

2 used two methods: parse () and format ()

 

2.1 string to date with the parse method

 

parse () is simple to use as follows:

 

1) construct a SimpleDateFormat object, the constructor argument passed when 'yyyy-MM-dd' representatives in date-01-01 'The date format

 

2) holds a string to be transferred

 

3) Use the SimpleDateFormat parse () method

 

  

1 public static void main(String[] args) throws ParseException { 
2     SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd"); 
3     String s = "2013-01-01"; 
4     Date date = simpleDateFormat.parse(s); 
5 }

 

 

2.2 date to a string using the format method

 

format () is simple to use as follows:

 

1) construct a SimpleDateFormat object, the constructor argument passed when 'yyyy-MM-dd' representatives in date-01-01 'The date format

 

2) held by a date to be transferred object

 

3) Use the SimpleDateFormat format () method

 

  

1 public static void main(String[] args) throws ParseException { 
2     SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd"); 
3     Date date = new Date(); 
4     String s = simpleDateFormat.format(date); 
5 }

 

 

3 constructor parameters when SimpleDateFormat Pattern

 

Pattern of the Chinese meaning as a model, samples, where we can be understood as the date for the provisions of the template.

 

  

这样我们就很好的理解了前言部分的代码为什么会出错了，因为它在使用parse()转换的时候没按常理出牌，待转换的String对象和规定的模板完全不同，即"2012-12-12"和"yyyy-MM-dd HH:mm:ss"是不同的样式

 

 So how should

Pattern provides? Java API gives the following specifications:

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

Letter	Date or Time Component	Presentation	Examples
G	Era designator	Text	AD
y	Year	Year	1996 ; 96
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 in week	Text	Tuesday ; Tue
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

 

Examples of the column is the sample values ​​(U.S. standard), Java API also gives some examples of between dates and strings, but also the U.S. standards.

                                                                                                                                                                                             

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

 

Perhaps you are more concerned about is that as China's developers some common date formats which, wait, then see below.

                                                                                                   

Date and Time Pattern	Result
"yyyy-MM-dd HH: mm: ss E"	2013-07-04 14:23:55 Thursday
"yyyy years at MM-dd HH mm minutes ss seconds when E"	2013 年 07 月 04 日 14 时 24 分 44 秒 Thursday
" yy / MM / dd HH: mm: ss E "	13/07/04 14:25:33 Thursday
"D-day of the first year, the first year w weeks in January in the first week of W, k in the day when, in the first time zone Z '< / span>	the first 185 days of the year, the year's first 27 weeks, in January the first one week, the day 14:00, in the first time zone +0800

 

sample code is as follows:

 

  

 1 public static void main(String[] args) throws ParseException {     
 2     SimpleDateFormat format1 = new SimpleDateFormat("yyy-MM-dd HH:mm:ss E"); 
 3     SimpleDateFormat format2 = new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒 E"); 
 4     SimpleDateFormat format3 = new SimpleDateFormat("yy/MM/dd HH:mm:ss E"); 
 5     SimpleDateFormat format4 = new SimpleDateFormat("一年中的第D天，一年中的第w个星期，一月中的第W个星期，在一天中k时，在第Z时区"); 
 6     Date date = new Date(); 
 7     System.out.println(format1.format(date)); 
 8     System.out.println(format2.format(date)); 
 9     System.out.println(format3.format(date)); 
10     System.out.println(format4.format(date)); 
11 }