java.util.ResourceBundle
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JavaTM 2 Platform Std. Ed. v1.4.2 |
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java.lang.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:
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 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(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
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.
ListResourceBundle,
PropertyResourceBundle,
MissingResourceException| Field Summary | |
protected ResourceBundle |
parent
The parent bundle of this bundle. |
| 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. |
protected abstract Object |
handleGetObject(String key)
Gets an object for the given key from this resource bundle. |
protected void |
setParent(ResourceBundle parent)
Sets 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
getObject
when this bundle does not contain a particular resource.
| Constructor Detail |
public ResourceBundle()
| Method Detail |
public final String getString(String key)
(String) getObject(key).
key - the key for the desired string
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 stringpublic final String[] getStringArray(String key)
(String[]) getObject(key).
key - the key for the desired string array
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 arraypublic final Object getObject(String key)
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.
key - the key for the desired object
NullPointerException - if key is null
MissingResourceException - if no object for the given key can be foundpublic Locale getLocale()
protected void setParent(ResourceBundle parent)
getObject
when this bundle does not contain a particular resource.
parent - this bundle's parent bundle.public static final ResourceBundle getBundle(String baseName)
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.
baseName - the base name of the resource bundle, a fully qualified class name
NullPointerException - if baseName is null
MissingResourceException - if no resource bundle for the specified base name can be found
public static final ResourceBundle getBundle(String baseName,
Locale locale)
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.
baseName - the base name of the resource bundle, a fully qualified class namelocale - the locale for which a resource bundle is desired
NullPointerException - if baseName or locale is null
MissingResourceException - if no resource bundle for the specified base name can be found
public static ResourceBundle getBundle(String baseName,
Locale locale,
ClassLoader 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):
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:
getBundle creates a new instance of this class and uses it as the result
resource bundle.
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 PropertyResourceBundles 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:
baseName - the base name of the resource bundle, a fully qualified class namelocale - the locale for which a resource bundle is desiredloader - the class loader from which to load the resource bundle
NullPointerException - if baseName, locale, or loader is null
MissingResourceException - if no resource bundle for the specified base name can be foundprotected abstract Object handleGetObject(String key)
key - the key for the desired object
NullPointerException - if key is nullpublic abstract Enumeration getKeys()
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JavaTM 2 Platform Std. Ed. v1.4.2 |
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