SimpleDateFormat and locale based format string

问题:

I'm trying to format a date in Java in different ways based on the given locale. For instance I want English users to see "Nov 1, 2009" (formatted by "MMM d, yyyy") and Norwegian users to see "1. nov. 2009" ("d. MMM. yyyy").

The month part works OK if I add the locale to the SimpleDateFormat constructor, but what about the rest?

I was hoping I could add format strings paired with locales to SimpleDateFormat, but I can't find any way to do this. Is it possible or do I need to let my code check the locale and add the corresponding format string?

回答1:

Use DateFormat.getDateInstance(int style, Locale locale) instead of creating your own patterns with SimpleDateFormat.

回答2:

SimpleDateFormat dateFormat = new SimpleDateFormat("EEEE dd MMM yyyy", Locale.ENGLISH);
String formatted = dateFormat.format(the_date_you_want_here);

回答3:

Use the style + locale: DateFormat.getDateInstance(int style, Locale locale)

Check http://java.sun.com/j2se/1.5.0/docs/api/java/text/DateFormat.html

Run the following example to see the differences:

import java.text.DateFormat;
import java.util.Date;
import java.util.Locale;

public class DateFormatDemoSO {
  public static void main(String args[]) {
    int style = DateFormat.MEDIUM;
    //Also try with style = DateFormat.FULL and DateFormat.SHORT
    Date date = new Date();
    DateFormat df;
    df = DateFormat.getDateInstance(style, Locale.UK);
    System.out.println("United Kingdom: " + df.format(date));
    df = DateFormat.getDateInstance(style, Locale.US);
    System.out.println("USA: " + df.format(date));   
    df = DateFormat.getDateInstance(style, Locale.FRANCE);
    System.out.println("France: " + df.format(date));
    df = DateFormat.getDateInstance(style, Locale.ITALY);
    System.out.println("Italy: " + df.format(date));
    df = DateFormat.getDateInstance(style, Locale.JAPAN);
    System.out.println("Japan: " + df.format(date));
  }
}

Output:

United Kingdom: 25-Sep-2017
USA: Sep 25, 2017
France: 25 sept. 2017
Italy: 25-set-2017
Japan: 2017/09/25

回答4:

tl;dr

LocalDate.now().format(
    DateTimeFormatter.ofLocalizedDate( FormatStyle.MEDIUM )
                     .withLocale( new Locale( "no" , "NO" ) )
)

The troublesome classes of java.util.Date and SimpleDateFormat are now legacy, supplanted by the java.time classes.

LocalDate

The LocalDate class represents a date-only value without time-of-day and without time zone.

A time zone is crucial in determining a date. For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight in Paris France is a new day while still “yesterday” in Montréal Québec.

ZoneId z = ZoneId.of( "America/Montreal" );
LocalDate today = LocalDate.now( z );

DateTimeFormatter

Use DateTimeFormatter to generate strings representing only the date-portion or the time-portion.

The DateTimeFormatter class can automatically localize.

To localize, specify:

• FormatStyle to determine how long or abbreviated should the string be.
• Locale to determine (a) the human language for translation of name of day, name of month, and such, and (b) the cultural norms deciding issues of abbreviation, capitalization, punctuation, and such.

Example:

Locale l = Locale.CANADA_FRENCH ; 
DateTimeFormatter f = DateTimeFormatter.ofLocalizedDate( FormatStyle.FULL ).withLocale( l );
String output = ld.format( f );

Going the other direction, you can parse a localized string.

LocalDate ld = LocalDate.parse( input , f );

Note that the locale and time zone are completely orthogonal issues. You can have a Montréal moment presented in Japanese language or an Auckland New Zealand moment presented in Hindi language.

Another example: Change 6 junio 2012 (Spanish) to 2012-06-06 (standard ISO 8601 format). The java.time classes use ISO 8601 formats by default for parsing/generating strings.

String input = "6 junio 2012";
Locale l = new Locale ( "es" , "ES" );
DateTimeFormatter f = DateTimeFormatter.ofPattern ( "d MMMM uuuu" , l );
LocalDate ld = LocalDate.parse ( input , f );
String output = ld.toString();  // 2012-06-06. 

Peruse formats

Here is some example code for perusing the results of multiple formats in multiple locales, automatically localized.

An EnumSet is an implementation of Set, highly optimized for both low memory usage and fast execution speed when collecting Enum objects. So, EnumSet.allOf( FormatStyle.class ) gives us a collection of all four of the FormatStyle enum objects to loop. For more info, see Oracle Tutorial on enum types.

LocalDate ld = LocalDate.of( 2018 , Month.JANUARY , 23 );

List < Locale > locales = new ArrayList <>( 3 );
locales.add( Locale.CANADA_FRENCH );
locales.add( new Locale( "no" , "NO" ) );
locales.add( Locale.US );

// Or use all locales (almost 800 of them, for about 120K text results).
// Locale[] locales = Locale.getAvailableLocales(); // All known locales. Almost 800 of them.

for ( Locale locale : locales )
{
    System.out.println( "------|  LOCALE: " + locale + " — " + locale.getDisplayName() + "  |----------------------------------" + System.lineSeparator() );

    for ( FormatStyle style : EnumSet.allOf( FormatStyle.class ) )
    {
        DateTimeFormatter f = DateTimeFormatter.ofLocalizedDate( style ).withLocale( locale );
        String output = ld.format( f );
        System.out.println( output );
    }
    System.out.println( "" );
}
System.out.println( "« fin »" + System.lineSeparator() );

Output.

------|  LOCALE: fr_CA — French (Canada)  |----------------------------------

mardi 23 janvier 2018
23 janvier 2018
23 janv. 2018
18-01-23

------|  LOCALE: no_NO — Norwegian (Norway)  |----------------------------------

tirsdag 23. januar 2018
23. januar 2018
23. jan. 2018
23.01.2018

------|  LOCALE: en_US — English (United States)  |----------------------------------

Tuesday, January 23, 2018
January 23, 2018
Jan 23, 2018
1/23/18

« fin »

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

回答5:

Localization of date string:

Based on redsonic's post:

private String localizeDate(String inputdate, Locale locale) { 

    Date date = new Date();
    SimpleDateFormat dateFormatCN = new SimpleDateFormat("dd-MMM-yyyy", locale);       
    SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MMM-yyyy");


    try {
        date = dateFormat.parse(inputdate);
    } catch (ParseException e) {
        log.warn("Input date was not correct. Can not localize it.");
        return inputdate;
    }
    return dateFormatCN.format(date);
}

String localizedDate = localizeDate("05-Sep-2013", new Locale("zh","CN"));

will be like 05-九月-2013

回答6:

This will display the date according to user's current locale:

import java.text.DateFormat;    
import java.util.Date;

Date date = new Date();
DateFormat df = DateFormat.getDateTimeInstance();
String myDate = df.format(date);

Dec 31, 1969 7:00:02 PM

DateFormat.getDateInstance() 

Dec 31, 1969

回答7:

String text = new SimpleDateFormat("E, MMM d, yyyy").format(date);

回答8:

Java 8 Style for a given date

LocalDate today = LocalDate.of(1982, Month.AUGUST, 31);
System.out.println(today.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(Locale.ENGLISH)));
System.out.println(today.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(Locale.FRENCH)));
System.out.println(today.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(Locale.JAPANESE)));

回答9:

Java8

 import java.time.format.DateTimeFormatter;         
 myDate.format(DateTimeFormatter.ofPattern("dd-MMM-YYYY",new Locale("ar")))