Using Resource Bundle

ResourceBundle is a class used for containing locale-specific data. A Locale defines the user's environment particularly its language and region. A certain number in one locale may be written differently in another. Likewise, a label of a "Cancel" button may differ in different locales. Using ResourceBundle will allow you to handle these different locales without having to hard-code the locale-specific data.

Sample of retrieving locale-specific data
list of resource bundles:
ButtonLabel
ButtonLabel_de
ButtonLabel_en_GB
ButtonLabel_fr_CA_UNIX

selecting the locale-specific ButtonLabel resource bundle:
Locale currentLocale = new Locale("fr", "CA", "UNIX");
ResourceBundle introLabels =
ResourceBundle.getBundle("ButtonLabel", currentLocale);

2 Types of ResourceBundle

1. PropertyResourceBundle - uses a properties file to contain the key-value pairs. The value can only be a String.
   

   
   properties files for 3 resource bundles:
   LabelsBundle.properties
   LabelsBundle_de.properties
   LabelsBundle_fr.properties
   
   resource bundle sample content:
   # This is the LabelsBundle_de.properties file
   s1 = Computer
   s2 = Platte
   s3 = Monitor
   s4 = Tastatur
   
   use of resource bundle sample:
         Locale[] supportedLocales = {
            Locale.FRENCH,
            Locale.GERMAN,
            Locale.ENGLISH
         };
   
         for (int i = 0; i < supportedLocales.length; i ++) {
            ResourceBundle labels = 
               ResourceBundle.getBundle("LabelsBundle",currentLocale);
   
            String value = labels.getString(key);
            Enumeration bundleKeys = labels.getKeys();
            while (bundleKeys.hasMoreElements()) {
               String key = (String)bundleKeys.nextElement();
               String value  = labels.getString(key);         
            }
         }
   



2. ListResourceBundle - uses a list to contain the key-value pairs. The value can be any object.
   

   
   3 resource bundles:
   StatsBundle_en_CA.class
   StatsBundle_fr_FR.class
   StatsBundle_ja_JP.class
   
   resource bundle sample:
   import java.util.*;
   public class StatsBundle_ja_JP extends ListResourceBundle {
       public Object[][] getContents() {
    return contents;
       }
       private Object[][] contents = {
    { "GDP", new Integer(21300) },
    { "Population", new Integer(125449703) },
    { "Literacy", new Double(0.99) },
       };
   }
   
   use of resource bundle sample:
         Locale[] supportedLocales = {
            new Locale("en","CA"),
            new Locale("ja","JP"),
            new Locale("fr","FR")
         };
   
         for (int i = 0; i < supportedLocales.length; i ++) {
            ResourceBundle stats = 
               ResourceBundle.getBundle("StatsBundle",currentLocale);
   
            Integer gdp = (Integer)stats.getObject("GDP");
         }
   

Notes:
- things to check/consider when internationalizing: http://java.sun.com/docs/books/tutorial/i18n/intro/checklist.html
- numbers, dates, times, or currencies need not be isolated in a ResourceBundle because only the display format of these objects varies with Locale, the objects themselves do not
- it is better to have multiple ResourceBundle by determining related objects and grouping them together
- ResourceBundle.Control class provides a way to control the instantiation and location of resource bundles. You can override its methods to behave differently.
- list of language codes (ISO-639): http://ftp.ics.uci.edu/pub/ietf/http/related/iso639.txt
- list of country codes (ISO-3166): http://userpage.chemie.fu-berlin.de/diverse/doc/ISO_3166.html

Source: http://java.sun.com/docs/books/tutorial/i18n/resbundle/index.html