ResourceBundle

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## java.util
Class ResourceBundle

    java.lang.Object
      java.util.ResourceBundle

Direct Known Subclasses:
  ListResourceBundle, PropertyResourceBundle

    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

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

Keys are always `String`s. In this example, the keys are "OkKey" and "CancelKey". In the above example, the values are also `String`s--"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(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`.

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 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.

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 following is a very simple example of a `ResourceBundle` subclass, MyResources, that manages two resources (for a larger number of resources you would probably use a `Hashtable`). Notice that you don't need to supply a value if a "parent-level" `ResourceBundle` handles the same key with the same value (as for the okKey below).

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;
>          }
>      }

>      // 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;
>          }
>      }

You do not have to restrict yourself to using a single family of `ResourceBundle`s. 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.

Since:
  JDK1.1
See Also:
  `ListResourceBundle`, `PropertyResourceBundle`, `MissingResourceException`

Constructor Summary
`ResourceBundle()` Sole constructor.

Method Summary
`static ResourceBundle` | `getBundle(String baseName)` Gets a resource bundle using the specified base name, the default locale, and the caller's class loader.
`static ResourceBundle` | `getBundle(String baseName, Locale locale)` Gets a resource bundle using the specified base name and locale, and the caller's class loader.
`static ResourceBundle` | `getBundle(String baseName, Locale locale, ClassLoader loader)` Gets a resource bundle using the specified base name, locale, and class loader.
`abstract Enumeration` | `getKeys()` Returns an enumeration of the keys.
`Locale` | `getLocale()` Returns the locale of this resource bundle.
`Object` | `getObject(String key)` Gets an object for the given key from this resource bundle or one of its parents.
`String` | `getString(String key)` Gets a string for the given key from this resource bundle or one of its parents.
`String[]` | `getStringArray(String key)` Gets a string array for the given key from this resource bundle or one of its parents.

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### ResourceBundle

    public ResourceBundle()

  Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

### getString

    public final String getString(String key)

  Gets a string for the given key from this resource bundle or one of its parents. Calling this method is equivalent to calling

  > `(String) `getObject`(key)`.

  Parameters:
    `key` - the key for the desired string
  Returns:
    the string for the given key
  Throws:
    `NullPointerException` - if `key` is `null`
    `MissingResourceException` - if no object for the given key can be found
    `ClassCastException` - if the object found for the given key is not a string

### getStringArray

    public final String[] getStringArray(String key)

  Gets a string array for the given key from this resource bundle or one of its parents. Calling this method is equivalent to calling

  > `(String[]) `getObject`(key)`.

  Parameters:
    `key` - the key for the desired string array
  Returns:
    the string array for the given key
  Throws:
    `NullPointerException` - if `key` is `null`
    `MissingResourceException` - if no object for the given key can be found
    `ClassCastException` - if the object found for the given key is not a string array

### getObject

    public final Object getObject(String key)

  Gets an object for the given key from this resource bundle or one of its parents. This method first tries to obtain the object from this resource bundle using `handleGetObject`. If not successful, and the parent resource bundle is not null, it calls the parent's `getObject` method. If still not successful, it throws a MissingResourceException.

  Parameters:
    `key` - the key for the desired object
  Returns:
    the object for the given key
  Throws:
    `NullPointerException` - if `key` is `null`
    `MissingResourceException` - if no object for the given key can be found

### getLocale

    public Locale getLocale()

  Returns the locale of this resource bundle. This method can be used after a call to getBundle() to determine whether the resource bundle returned really corresponds to the requested locale or is a fallback.

  Returns:
    the locale of this resource bundle

### getBundle

    public static final ResourceBundle getBundle(String baseName)

  Gets a resource bundle using the specified base name, the default locale, and the caller's class loader. Calling this method is equivalent to calling

  > `getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader())`,

  except that `getClassLoader()` is run with the security privileges of `ResourceBundle`. See `getBundle` for a complete description of the search and instantiation strategy.

  Parameters:
    `baseName` - the base name of the resource bundle, a fully qualified class name
  Returns:
    a resource bundle for the given base name and the default locale
  Throws:
    `NullPointerException` - if `baseName` is `null`
    `MissingResourceException` - if no resource bundle for the specified base name can be found

### getBundle

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

  Gets a resource bundle using the specified base name and locale, and the caller's class loader. Calling this method is equivalent to calling

  > `getBundle(baseName, locale, this.getClass().getClassLoader())`,

  except that `getClassLoader()` is run with the security privileges of `ResourceBundle`. See `getBundle` for a complete description of the search and instantiation strategy.

  Parameters:
    `baseName` - the base name of the resource bundle, a fully qualified class name
    `locale` - the locale for which a resource bundle is desired
  Returns:
    a resource bundle for the given base name and locale
  Throws:
    `NullPointerException` - if `baseName` or `locale` is `null`
    `MissingResourceException` - if no resource bundle for the specified base name can be found

### getBundle

    public static ResourceBundle getBundle(String baseName,
                                           Locale locale,
                                           ClassLoader loader)

  Gets a resource bundle using the specified base name, locale, and class loader.

  Conceptually, `getBundle` uses the following strategy for locating and instantiating resource bundles:

  `getBundle` uses the base name, the specified locale, and the default locale (obtained from `Locale.getDefault`) to generate a sequence of candidate bundle names. If the specified locale's language, country, and variant are all empty strings, then the base name is the only candidate bundle name. Otherwise, the following sequence is generated from the attribute values of the specified locale (language1, country1, and variant1) and of the default locale (language2, country2, and variant2):

  - baseName + "_" + language1 + "_" + country1 + "_" + variant1
  - baseName + "_" + language1 + "_" + country1
  - baseName + "_" + language1
  - baseName + "_" + language2 + "_" + country2 + "_" + variant2
  - baseName + "_" + language2 + "_" + country2
  - baseName + "_" + language2
  - baseName

  Candidate bundle names where the final component is an empty string are omitted. For example, if country1 is an empty string, the second candidate bundle name is omitted.

  `getBundle` then iterates over the candidate bundle names to find the first one for which it can instantiate an actual resource bundle. For each candidate bundle name, it attempts to create a resource bundle:

  - First, it attempts to load a class using the candidate bundle name. If such a class can be found and loaded using the specified class loader, is assignment compatible with ResourceBundle, is accessible from ResourceBundle, and can be instantiated, `getBundle` creates a new instance of this class and uses it as the result resource bundle.
  - Otherwise, `getBundle` attempts to locate a property resource file. It generates a path name from the candidate bundle name by replacing all "." characters with "/" and appending the string ".properties". It attempts to find a "resource" with this name using `ClassLoader.getResource`. (Note that a "resource" in the sense of `getResource` has nothing to do with the contents of a resource bundle, it is just a container of data, such as a file.) If it finds a "resource", it attempts to create a new `PropertyResourceBundle` instance from its contents. If successful, this instance becomes the result resource bundle.

  If no result resource bundle has been found, a `MissingResourceException` is thrown.

  Once a result resource bundle has been found, its parent chain is instantiated. `getBundle` iterates over the candidate bundle names that can be obtained by successively removing variant, country, and language (each time with the preceding "_") from the bundle name of the result resource bundle. As above, candidate bundle names where the final component is an empty string are omitted. With each of the candidate bundle names it attempts to instantiate a resource bundle, as described above. Whenever it succeeds, it calls the previously instantiated resource bundle's `setParent` method with the new resource bundle, unless the previously instantiated resource bundle already has a non-null parent.

  Implementations of `getBundle` may cache instantiated resource bundles and return the same resource bundle instance multiple times. They may also vary the sequence in which resource bundles are instantiated as long as the selection of the result resource bundle and its parent chain are compatible with the description above.

  The `baseName` argument should be a fully qualified class name. However, for compatibility with earlier versions, Sun's Java 2 runtime environments do not verify this, and so it is possible to access `PropertyResourceBundle`s by specifying a path name (using "/") instead of a fully qualified class name (using ".").

  Example: The following class and property files are provided: MyResources.class, MyResources_fr_CH.properties, MyResources_fr_CH.class, MyResources_fr.properties, MyResources_en.properties, MyResources_es_ES.class. The contents of all files are valid (that is, public non-abstract subclasses of ResourceBundle for the ".class" files, syntactically correct ".properties" files). The default locale is `Locale("en", "GB")`.

  Calling `getBundle` with the shown locale argument values instantiates resource bundles from the following sources:

  - Locale("fr", "CH"): result MyResources_fr_CH.class, parent MyResources_fr.properties, parent MyResources.class
  - Locale("fr", "FR"): result MyResources_fr.properties, parent MyResources.class
  - Locale("de", "DE"): result MyResources_en.properties, parent MyResources.class
  - Locale("en", "US"): result MyResources_en.properties, parent MyResources.class
  - Locale("es", "ES"): result MyResources_es_ES.class, parent MyResources.class
  The file MyResources_fr_CH.properties is never used because it is hidden by MyResources_fr_CH.class.

  Parameters:
    `baseName` - the base name of the resource bundle, a fully qualified class name
    `locale` - the locale for which a resource bundle is desired
    `loader` - the class loader from which to load the resource bundle
  Returns:
    a resource bundle for the given base name and locale
  Throws:
    `NullPointerException` - if `baseName`, `locale`, or `loader` is `null`
    `MissingResourceException` - if no resource bundle for the specified base name can be found
  Since:
    1.2

### getKeys

    public abstract Enumeration getKeys()

  Returns an enumeration of the keys.

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