Resource Bundles

One of the strengths of the Java programming language is the variety of language and API mechanisms that promote internationalization. For example, Unicode characters (16 bits) support more character sets than the typical 8-bit character set used in other languages. One of the most important of these mechanisms is known as "resource bundles."

Resource bundles contain locale-specific objects. When your program needs a locale-specific resource, a String for example, your program can load it from the resource bundle that is appropriate for the current user's locale. In this way, you can write program code that is largely independent of the user's locale isolating most, if not all, of the locale-specific information in resource bundles.

This allows you to write programs that can:

• be easily localized, or translated, into different languages
• handle multiple locales at once
• be easily modified later to support even more locales

Resource bundles belong to families whose members share a common base name, but whose names also have additional components that identify their locales. For example, the base name of a family of resource bundles might be "MyResources". The family should have a default resource bundle which simply has the same name as its family - "MyResources" - and will be used as the bundle of last resort if a specific locale is not supported. The family can then provide as many locale-specific members as needed, for example a German one named "MyResources_de".

Each resource bundle in a family contains the same items, but the items have been translated for the locale represented by that resource bundle. For example, both "MyResources" and "MyResources_de" may have a String that's used on a button for canceling operations. In "MyResources" the String may contain "Cancel" and in "MyResources_de" it may contain "Abbrechen".

If there are different resources for different countries, you can make specializations: for example, "MyResources_de_CH" contains objects for the German language (de) in Switzerland (CH). If you want to only modify some of the resources in the specialization, you can do so.

#MyResources.properties file
OkKey=Ok
CancelKey=Cancel

#MyResources_de.properties file
#don't need okKey, since parent level handles it.
CancelKey= Abbrechen

When your program needs a locale-specific object, it loads the ResourceBundle class using the getBundle method:

ResourceBundle myResources =
     ResourceBundle.getBundle("MyResources", currentLocale);

or you can load ResourceBundle in German language

ResourceBundle myResources =
     ResourceBundle.getBundle("MyResources", Locale.GERMAN);

Resource bundles contain key/value pairs. The keys uniquely identify a locale-specific object in the bundle. Here's an example of a ListResourceBundle that contains two key/value pairs:

You retrieve an object from resource bundle using the appropriate getter method. Because "OkKey" and "CancelKey" are both strings, you would use getString to retrieve them:

button1 = new Button(myResources.getString("OkKey"));
button2 = new Button(myResources.getString("CancelKey"));

The getter methods all require the key as an argument and return the object if found. If the object is not found, the getter method throws a MissingResourceException .

The Java 2 platform provides two subclasses of ResourceBundle , ListResourceBundle and PropertyResourceBundle , that provide a fairly simple way to create resources. As you saw briefly in a previous example, ListResourceBundle manages its resource as a List of key/value pairs. PropertyResourceBundle uses a properties file to manage its resources.