Class java.util.ResourceBundle
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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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