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JavaTM 2 Platform Standard Edition |
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java.lang.Object | +--java.util.ResourceBundle
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:
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
is 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:
The first argument specifies the family name of the resource bundle that contains the object in question. The second argument indicates the desired locale.ResourceBundle myResources = ResourceBundle.getBundle("MyResources", currentLocale);
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 current default locale as returned by Locale.getDefault(), and (3) the root resource bundle (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 + "_" + language2 + "_" + country2 + "_" + variant2
baseclass + "_" + language2 + "_" + country2
baseclass + "_" + language2
baseclass
For example, if the current default locale is en_US, the locale the caller
is interested in is fr_CH, and the resource bundle name is MyResources,
resource bundle lookup will search for the following classes, in order:
MyResources_fr_CH
MyResources_fr
MyResources_en_US
MyResources_en
MyResources
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
NumberFormat
s, Collation
s, 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:
Keys are alwaysclass MyResource extends ListResourceBundle { public Object[][] getContents() { return contents; } static final Object[][] contents = { // LOCALIZE THIS {"OkKey", "OK"}, {"CancelKey", "Cancel"}, // END OF MATERIAL TO LOCALIZE }; }
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:
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 abutton1 = new Button(myResourceBundle.getString("OkKey")); button2 = new Button(myResourceBundle.getString("CancelKey"));
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. In fact, you must provide all of the classes in any given inheritance chain that you provide a resource for. For example, if you provide MyResources_fr_BE, you must provide both MyResources and MyResources_fr or the resource bundle lookup won't work right.
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 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 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 (as in United Kingdom below). Also notice that because
you specify an en_GB resource bundle, you also have to provide a default en
resource bundle even though it inherits all its data from the root resource bundle.
Example:
You do not have to restrict yourself to using a single family of// default (English language, United States) abstract 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) { if (key.equals("okKey")) return "Gut"; if (key.equals("cancelKey")) return "Vernichten"; return null; } } // English language, default (must provide even though all the data is // in the root locale) public class MyResources_en extends MyResources { public Object handleGetObject(String key) { return null; } } // English language, United Kingdom (Great Britain) public class MyResources_en_GB extends MyResources { public Object handleGetObject(String key) { // don't need okKey, since parent level handles it. if (key.equals("cancelKey")) return "Dispose"; return null; } }
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.
Field Summary | |
protected ResourceBundle |
parent
The parent bundle is consulted by getObject when this bundle does not contain a particular resource. |
Constructor Summary | |
ResourceBundle()
Sole constructor. |
Method Summary | |
static ResourceBundle |
getBundle(String baseName)
Get the appropriate ResourceBundle subclass. |
static ResourceBundle |
getBundle(String baseName,
Locale locale)
Get the appropriate ResourceBundle subclass. |
static ResourceBundle |
getBundle(String baseName,
Locale locale,
ClassLoader loader)
Get the appropriate ResourceBundle subclass. |
abstract Enumeration |
getKeys()
Return an enumeration of the keys. |
Locale |
getLocale()
Return the Locale for this ResourceBundle. |
Object |
getObject(String key)
Get an object from a ResourceBundle. |
String |
getString(String key)
Get an object from a ResourceBundle. |
String[] |
getStringArray(String key)
Get an object from a ResourceBundle. |
protected abstract Object |
handleGetObject(String key)
Get an object from a ResourceBundle. |
protected void |
setParent(ResourceBundle parent)
Set the parent bundle of this bundle. |
Methods inherited from class java.lang.Object |
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait |
Field Detail |
protected ResourceBundle parent
Constructor Detail |
public ResourceBundle()
Method Detail |
public final String getString(String key) throws MissingResourceException
key
- see class description.public final String[] getStringArray(String key) throws MissingResourceException
key
- see class description.public final Object getObject(String key) throws MissingResourceException
key
- see class description.public static final ResourceBundle getBundle(String baseName) throws MissingResourceException
baseName
- see class description.public static final ResourceBundle getBundle(String baseName, Locale locale)
baseName
- see class description.locale
- see class description.public Locale getLocale()
public static ResourceBundle getBundle(String baseName, Locale locale, ClassLoader loader) throws MissingResourceException
baseName
- see class description.locale
- see class description.loader
- the ClassLoader to load the resource fromprotected void setParent(ResourceBundle parent)
parent
- this bundle's parent bundle.protected abstract Object handleGetObject(String key) throws MissingResourceException
key
- see class description.public abstract Enumeration getKeys()
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JavaTM 2 Platform Standard Edition |
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