Just an example on how “java.text.SimpleDateFormat” can be used to convert a java date object (java.util.Date) to a string (String, StringBuffer, StringBuilder, etc..).
The whole magic is done by SimpleDateFormat, the child of “java.text.DateFormat”, which, as its name suggests, formats the date by a provided template.
This template is very flexible and provided to the formatter as a string. Here are the values which are used by SimpleDateFormat’s template:
| 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 |
Below, I wrote an example on how to implement the conversion. Here I used two different templates: “yyyyMMdd” and “MMddyyyy” to show that several letters from the table above can be used in different sequence for the desired format:
import java.util.Date; import java.text.SimpleDateFormat; ... ... ... ... public void testConvertDateToString() { // Allocates a Date object and initializes it so that it represents the time // at which it was allocated, measured to the nearest millisecond. Date dateNow = new Date (); SimpleDateFormat dateformatYYYYMMDD = new SimpleDateFormat("yyyyMMdd"); SimpleDateFormat dateformatMMDDYYYY = new SimpleDateFormat("MMddyyyy"); StringBuilder nowYYYYMMDD = new StringBuilder( dateformatYYYYMMDD.format( dateNow ) ); StringBuilder nowMMDDYYYY = new StringBuilder( dateformatMMDDYYYY.format( dateNow ) ); System.out.println( "DEBUG: Today in YYYYMMDD: '" + nowYYYYMMDD + "'"); System.out.println( "DEBUG: Today in MMDDYYYY: '" + nowMMDDYYYY + "'"); } |
Results:
DEBUG: Today in YYYYMMDD: ‘20070609’
DEBUG: Today in MMDDYYYY: ‘06092007’
You may also notice that in the example I used StringBuilder, and not String or StringBuffer. The reason is simple – “best practice – use the right tool for the right task”.
“String” is immutable, meaning it cannot be changed, every time you try to change it, new String object is created and the old one is released for garbage collection, therefore String can be perfect for something like constants e.g. { private static final String FORTY_TWO = “42”; }.
StringBuilder and StringBuffer can be changed (modified), and, in fact, they have exactly the same functionality with one distinct difference – StringBuffer is synchronized and StringBuilder is not. Therefore if the segment of code we are working on is not designed to be multi threaded (used by different threads in a same time), it is better to use StringBuilder, since it will work faster.
StringBuilder is available in Java 1.5.0 (Java 2 SE 5.0) and up.
KISS – Keep It Simple Stupid ;)