Class java.util.ResourceBundle - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.util.ResourceBundle

java.lang.Object
   |
   +----java.util.ResourceBundle

public abstract class ResourceBundle
extends Object

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

One resource bundle is, conceptually, a set of related classes that inherit from ResourceBundle. Each related subclass of ResourceBundle has the same base name plus an additional component that identifies its locale. For example, suppose your resource bundle is named MyResources. The first class you are likely to write is the default resource bundle which simply has the same name as its family--MyResources. You can also provide as many related locale-specific classes as you need: for example, perhaps you would provide a German one named MyResources_de.

Each related subclass of ResourceBundle contains the same items, but the items have been translated for the locale represented by that ResourceBundle subclass. For example, both MyResources and MyResources_de may have a String that's used on a button for confirming operations. In MyResources the String may contain OK and in MyResources_de it may contain Gut.

If there are different resources for different countries, you can make specializations: for example, MyResources_de_CH for Switzerland. 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);

The first argument specifies the family name of the resource bundle that contains the object in question. The second argument indicates the desired locale. getBundle uses these two arguments to construct the name of the ResourceBundle subclass it should load as follows.

The resource bundle lookup searches for classes with various suffixes on the basis of (1) the desired locale and (2) the default locale (baseclass), in the following order from lower-level (more specific) to parent-level (less specific):

baseclass + "_" + language1 + "_" + country1 + "_" + variant1
baseclass + "_" + language1 + "_" + country1
baseclass + "_" + language1
baseclass
baseclass + "_" + language2 + "_" + country2 + "_" + variant2
baseclass + "_" + language2 + "_" + country2
baseclass + "_" + language2

The result of the lookup is a class, but that class may be backed by a property file on disk. If a lookup fails, getBundle() throws a MissingResourceException.

The baseclass must be fully qualified (for example, myPackage.MyResources, not just MyResources). It must also be accessable by your code; it cannot be a class that is private to the package where ResourceBundle.getBundle is called.

Note: ResourceBundle are used internally in accessing NumberFormats, Collations, and so on. The lookup strategy is the same.

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:

 class MyResource extends ListResourceBundle {
      public Object[][] getContents() {
              return contents;
      }
      static final Object[][] contents = {
      // LOCALIZE THIS
              {"OkKey", "OK"},
              {"CancelKey", "Cancel"},
      // END OF MATERIAL TO LOCALIZE
      };
 }

Keys are always Strings. In this example, the keys are OkKey and CancelKey. In the above example, the values are also Strings--OK and Cancel--but they don't have to be. The values can be any type of object.

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(myResourceBundle.getString("OkKey"));
 button2 = new Button(myResourceBundle.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.

Besides getString; ResourceBundle supports a number of other methods for getting different types of objects such as getStringArray. If you don't have an object that matches one of these methods, you can use getObject and cast the result to the appropriate type. For example:

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

NOTE: You should always supply a baseclass with no suffixes. This will be the class of "last resort", if a locale is requested that does not exist. For example, below we have a class MyResources. It happens to contain US strings, so we don't have to have an explicit MyResource_en or MyResource_en_US.

The JDK provides two subclasses of ResourceBundle, ListResourceBundle and PropertyResourceBundle, that provide a fairly simple way to create resources. (Once serialization is fully integrated, we will provide another way.) As you saw briefly in a prevous 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 overrde two methods: handleGetObject and getKeys().

The following is a very simple example of a ResourceBundle subclass that manages only a few resources (for a larger number of resources you would probably use a Hashtable). Notice that if the key is not found, handleGetObject must return null. Notice also that you don't need to supply a value if a "parent-level" ResourceBundle handles the same key with the same value (look at uk below).

Example:

 abstract class MyResources extends ResourceBundle {
     public Object handleGetObject(String key) {
         if (key.equals("okKey")) return "Ok";
         if (key.equals("cancelKey")) return "Cancel";
 	   return null;
     }
 }
 abstract class MyResources_de extends MyResources {
     public Object handleGetObject(String key) {
         if (key.equals("okKey")) return "Gut";
         if (key.equals("cancelKey")) return "Vernichten";
         return null;
     }
 }
 abstract class MyResources_uk extends MyResources {
     public Object handleGetObject(String key) {
         // don't need okKey, since parent level handles it.
         if (key.equals("cancelKey")) return "Dispose";
     	   return null;
     }
 }

You do not have to restrict yourself to using a single family of ResourceBundles. For example, you could have a set of bundles for exception messages, ExceptionResources (ExceptionResources_fr, ExceptionResources_de, ...), and one for widgets, WidgetResource (WidgetResources_fr, WidgetResources_de, ...); breaking up the resources however you like.

See Also:: ListResourceBundle, PropertyResourceBundle, MissingResourceException

parent: The parent bundle is consulted by getObject when this bundle does not contain a particular resource.

ResourceBundle()

getBundle(String): Get the appropriate ResourceBundle subclass.
getBundle(String, Locale): Get the appropriate ResourceBundle subclass.
getKeys(): Return an enumeration of the keys.
getObject(String): Get an object from a ResourceBundle.
getString(String): Get an object from a ResourceBundle.
getStringArray(String): Get an object from a ResourceBundle.
handleGetObject(String): Get an object from a ResourceBundle.
setParent(ResourceBundle): Set the parent bundle of this bundle.

parent

 protected ResourceBundle parent

The parent bundle is consulted by getObject when this bundle does not contain a particular resource.

ResourceBundle

 public ResourceBundle()

getString

 public final String getString(String key) throws MissingResourceException

Get an object from a ResourceBundle.
Convenience method to save casting.

Parameters:: key - see class description.

getStringArray

 public final String[] getStringArray(String key) throws MissingResourceException

Get an object from a ResourceBundle.
Convenience method to save casting.

Parameters:: key - see class description.

getObject

 public final Object getObject(String key) throws MissingResourceException

Get an object from a ResourceBundle.

Parameters:: key - see class description.

getBundle

 public static final ResourceBundle getBundle(String baseName) throws MissingResourceException

Get the appropriate ResourceBundle subclass.

Parameters:: baseName - see class description.

getBundle

 public static final ResourceBundle getBundle(String baseName,
                                              Locale locale)

Get the appropriate ResourceBundle subclass.

Parameters:: baseName - see class description.; locale - see class description.

setParent

 protected void setParent(ResourceBundle parent)

Set the parent bundle of this bundle. The parent bundle is searched by getObject when this bundle does not contain a particular resource.

Parameters:: parent - this bundle's parent bundle.

handleGetObject

 protected abstract Object handleGetObject(String key) throws MissingResourceException

Get an object from a ResourceBundle. NOTE: Subclasses must override.

Parameters:: key - see class description.

getKeys

 public abstract Enumeration getKeys()

Return an enumeration of the keys. NOTE: Subclasses must override.

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