ResourceBundle

abstract class ResourceBundle

Resource bundles contain locale-specific objects. When your program needs a locale-specific resource, a 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.

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

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

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:

public class MyResources extends ListResourceBundle {
      protected Object[][] getContents() {
          return new Object[][] {
              // LOCALIZE THE SECOND STRING OF EACH ARRAY (e.g., "OK")
              {"OkKey", "OK"},
              {"CancelKey", "Cancel"},
              // END OF MATERIAL TO LOCALIZE
         };
      }
  }
  

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"));
  

Besides getString, ResourceBundle also provides a method for getting string arrays, getStringArray, as well as a generic getObject method for any other type of object. When using getObject, you'll have to cast the result to the appropriate type. For example:

int[] myIntegers = (int[]) myResources.getObject("intList");
  

The Java 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.

If ListResourceBundle or PropertyResourceBundle do not suit your needs, you can write your own ResourceBundle subclass. Your subclasses must override two methods: handleGetObject and getKeys().

The implementation of a ResourceBundle subclass must be thread-safe if it's simultaneously used by multiple threads. The default implementations of the non-abstract methods in this class, and the methods in the direct known concrete subclasses ListResourceBundle and PropertyResourceBundle are thread-safe.

ResourceBundle.Control

Cache Management

Example

// default (English language, United States)
  public class MyResources extends ResourceBundle {
      public Object handleGetObject(String key) {
          if (key.equals("okKey")) return "Ok";
          if (key.equals("cancelKey")) return "Cancel";
          return null;
      }
 
      public Enumeration<String> getKeys() {
          return Collections.enumeration(keySet());
      }
 
      // Overrides handleKeySet() so that the getKeys() implementation
      // can rely on the keySet() value.
      protected Set<String> handleKeySet() {
          return new HashSet<String>(Arrays.asList("okKey", "cancelKey"));
      }
  }
 
  // German language
  public class MyResources_de extends MyResources {
      public Object handleGetObject(String key) {
          // don't need okKey, since parent level handles it.
          if (key.equals("cancelKey")) return "Abbrechen";
          return null;
      }
 
      protected Set<String> handleKeySet() {
          return new HashSet<String>(Arrays.asList("cancelKey"));
      }
  }
  

Summary

Public constructors

ResourceBundle()

Public methods

static fun clearCache(): Unit

static fun clearCache(loader: ClassLoader!): Unit

open fun containsKey(key: String!): Boolean

open fun getBaseBundleName(): String!

static fun getBundle(baseName: String!): ResourceBundle!

static fun getBundle(
    baseName: String!, 
    locale: Locale!
): ResourceBundle!

open static fun getBundle(
    baseName: String!, 
    locale: Locale!, 
    loader: ClassLoader!
): ResourceBundle!

getBundle(baseName, targetLocale, loader, control)