Java printing Date/Time in a Given Format

Java printing Date/Time in a Given Format

Problem

You want to print the date and/or time in a locale-sensitive or otherwise-specified
format.

Solution

Use java.text.DateFormat .

Explained

To print the date in the correct format for whatever locale your software lands in,
simply use the default DateFormat formatter, which is obtained by calling DateFormat.
getInstance( ) :

import java.util.*;
import java.text.*;
public class DateFormatBest {
public static void main(String[] args) {
Date today = new Date( );
DateFormat df = DateFormat.getInstance( );
System.out.println(df.format(today));
DateFormat df_fr =
DateFormat.getDateInstance(DateFormat.FULL, Locale.FRENCH);
System.out.println(df_fr.format(today));
}
}

When I run this, it prints:

3/3/04 12:17 PM
mercredi 3 mars 2004

You can ask for a default date and time formatter ( df in the example), or a TimeFormatter or DateFormatter that extracts just the time or date portion of the Date object ( df_fr in the example). You can also request a nondefault Locale ( df_fr in the example). Five codes—FULL, LONG, MEDIUM, SHORT and DEFAULT—can be passed to describe how verbose a format you want. Suppose you want the date printed, but instead of the default format, you want it printed like “Sun 2004.07.18 at 04:14:09 PM PDT”. A look at the Javadoc page for SimpleDateFormat —the only nonabstract subclass of DateFormat —reveals that it has a rich language for specifying date and time formatting. Be aware that in so doing you are presuming to know the correct format in all locales; see Chapter 15 for why this may be a bad idea. To use a default format, of course, we can just use the Date object’s toString( ) method, and for a localized default format, we use DateFormat.getInstance( ) . But to have full control and get the “Sun 2004.07.18 at 04:14:09 PM PDT”, we construct an instance explicitly, like so:

new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");

E means the day of the week; yyyy , MM , and dd are obviously year, month, and day. The quoted string 'at' means the string “at”. hh:mm:ss is the time; a means A.M. or P.M., and zzz means the time zone. Some of these are more memorable than others; I find the zzz tends to put me to sleep. Here’s the code:

// DateDemo.java
Date dNow = new Date( );
/* Simple, Java 1.0 date printing */
System.out.println("It is now " + dNow.toString( ));
// Use a SimpleDateFormat to print the date our way.
SimpleDateFormat formatter
= new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
System.out.println("It is " + formatter.format(dNow));

You can use as many of the given symbols as needed. Where a format can be used either in text or numeric context, you can set it to a longer form by repetitions of the character. For codes marked Text , four or more pattern letters cause the formatter to use the long form; fewer cause it to use the short or abbreviated form if one exists. Thus, E might yield Mon, whereas EEEE would yield Monday. For those marked Number , the number of repetitions of the symbol gives the minimum number of dig- its. Shorter numbers are zero-padded to the given number of digits. The year is han- dled specially: yy yields an ambiguous * two-digit year (98, 99, 00, 01...), whereas yyyy yields a valid year (2001). For those marked Text and Number , three or more symbols causes the formatter to use text, while one or two make it use a number: MM might yield 01, while MMM would yield January.