How to Use SimpleDateFormat Class Formating/Parsing Date and Time?

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SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. SimpleDateFormat allows you to start by choosing any user-defined patterns for date-time formatting. DateFormat also provides many class methods for obtaining default date/time formatters based on the default or a given locale and a number of formatting styles. The SimpleDateFormat provides more flexiable custom formats for date time,  you can set your own date patterns. The following document is from Java API Document.

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
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

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

For example,the following code will format the current date time to the same date time pattern as the output of Date class's toString method.

import java.text.SimpleDateFormat;
import java.util.Date;

public class SimpleDateFormatExample {

    public static void main(String[] args) {
  
        Date now = new Date();
        String datetimeStr = now.toString();
        System.out.println("1. " + datetimeStr);
        SimpleDateFormat format = new SimpleDateFormat(
                    "EEE MMM dd HH:mm:ss zzz yyyy");
        System.out.println("2. " + format.format(now));
    }

}

The output is

1. Fri Jun 27 21:28:16 EDT 2008
2. Fri Jun 27 21:28:16 EDT 2008
 

The following example shows how to parse date time string by using SimpleDateFormat:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class SimpleDateFormatExample {

    public static void main(String[] args) {

        Date now = new Date();
        String datetimeStr = now.toString();
        SimpleDateFormat format = new SimpleDateFormat(
                   "EEE MMM dd HH:mm:ss zzz yyyy");
        try {
            Date parseDate = format.parse(datetimeStr);
            System.out.println(parseDate.toString());
        } 
        catch (ParseException e) {
            ;
        }
        
    }

}

The output is

Fri Jun 27 21:40:52 EDT 2008