Presents your 
JAVA E-NEWSLETTER for May 12, 2003

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USE RESOURCE BUNDLES FOR INTERNATIONALIZATION

Resource bundles, which have been a part of Java since 1.1, allow you to
store and access locale-specific resource objects for use in your application.

The simplest example of a locale-specific resource is probably a String
object. For example, in the application below, the output needs to be a
different message depending on the locale specified on the command line.
To create an instance of a resource bundle, use the static method:

java.util.ResourceBundle.getBundle():

ResourceBundle messages = ResourceBundle.getBundle("messages",Locale.ENGLISH);

The getBundle() method has three forms that allow you to choose a
specific locale and classloader, or you can choose to let them default to the
default locale and classloader.

As you can see from the preceding example code, getting an instance of a
resource bundle is almost trivial. The example code locale is English,
so when the method call above is executed, ResourceBundle searched the
application's classpath for a file named "messages_en.properties". If the
file is not found, a java.util.MissingResourceException error is thrown.

In a real application, you would choose your locale based on a user
action or system setting. Below is an example that selects the locale based
on an argument passed at start up:

Locale locale = Locale.ENGLISH;
        
if ( args.length != 0 ) {
    locale = new Locale(args[0]);
}
        
ResourceBundle messages = ResourceBundle.getBundle("messages", locale);

After you have an instance of resource bundle, you then call one of the
get methods to get the localized resource you want.

The ResourceBundle type defines methods for getting strings, arrays of
strings, and objects. In this case, a String welcome message is the target:

String message = messages.getString("welcome.message");

When the getString() method is called, the ResourceBundle looks for a
String object in the previously loaded properties files that has the key
name "welcome.message". If the key cannot be found, a
java.util.MissingResourceException error is thrown.

The properties files that are used look like this:

messages_en.properties:
welcome.message=Welcome to fantastic application and thanks for 
choosing  Acme, Inc.

messages_de.properties
welcome.message=Heibetaen Sie willkommen zu phantastischer Anwendung und
Dank zum Wahlen von Gipfel, Inc.

messages_fr.properties:
welcome.message=Bienvenu a l'application fantastique et remercie pour
choisir de Point Culminant, Inc.

(Please note that the text above was converted to French and German
using an automatic translator.)

You can use resource bundles for other objects besides strings. For
instance, you can create your own implementations of resource bundles that
are independent of properties files. Whether you need to store
locale-specific strings or you need to handle more complex objects, 
resource bundles offer you a choice.

import java.util.Locale;
import java.util.ResourceBundle;


public class ResourceBundleTip {
    public static void main(String[] args) {
        Locale locale = Locale.ENGLISH;
        
        if ( args.length != 0 ) {
            locale = new Locale(args[0]);
        }
        
        ResourceBundle messages = ResourceBundle.getBundle("messages",
locale);
        String message = messages.getString("welcome.message");
        
        System.out.println(message);    
    }
}

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