|
Java™ Platform Standard Ed. 6 |
|||||||||
PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
java.lang.Object java.util.ResourceBundle
public abstract class 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:
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:
Keys are alwayspublic class MyResources extends ListResourceBundle { protected Object[][] getContents() { return new Object[][] { // LOCALIZE THE SECOND STRING OF EACH ARRAY (e.g., "OK") {"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(myResources.getString("OkKey")); button2 = new Button(myResources.getString("CancelKey"));
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 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()
.
ResourceBundle.Control
class provides information necessary
to perform the bundle loading process by the getBundle
factory methods that take a ResourceBundle.Control
instance. You can implement your own subclass in order to enable
non-standard resource bundle formats, change the search strategy, or
define caching parameters. Refer to the descriptions of the class and the
getBundle
factory method for details.
getBundle
factory
methods are cached by default, and the factory methods return the same
resource bundle instance multiple times if it has been
cached. getBundle
clients may clear the cache, manage the
lifetime of cached resource bundle instances using time-to-live values,
or specify not to cache resource bundle instances. Refer to the
descriptions of the getBundle
factory method, clearCache
, ResourceBundle.Control.getTimeToLive
, and ResourceBundle.Control.needsReload
for details.
ResourceBundle
subclass, MyResources
, that manages two resources (for a larger number of
resources you would probably use a Map
).
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).
You do not have to restrict yourself to using a single family of// 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; } public Enumeration<String> getKeys() { return Collections.enumeration(keySet()); } // Overrides handleKeySet() so that the getKeys() implementation // can rely on the keySet() value. protected Set<String> handleKeySet() { return new HashSet<String>(Arrays.asList("okKey", "cancelKey")); } } // 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; } protected Set<String> handleKeySet() { return new HashSet<String>(Arrays.asList("cancelKey")); } }
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.
ListResourceBundle
,
PropertyResourceBundle
,
MissingResourceException
Nested Class Summary | |
---|---|
static class |
ResourceBundle.Control
ResourceBundle.Control defines a set of callback methods
that are invoked by the ResourceBundle.getBundle factory
methods during the bundle loading process. |
Field Summary | |
---|---|
protected ResourceBundle |
parent
The parent bundle of this bundle. |
Constructor Summary | |
---|---|
ResourceBundle()
Sole constructor. |
Method Summary | |
---|---|
static void |
clearCache()
Removes all resource bundles from the cache that have been loaded using the caller's class loader. |
static void |
clearCache(ClassLoader loader)
Removes all resource bundles from the cache that have been loaded using the given class loader. |
boolean |
containsKey(String key)
Determines whether the given key is contained in
this ResourceBundle or its parent bundles. |
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. |
static ResourceBundle |
getBundle(String baseName,
Locale targetLocale,
ClassLoader loader,
ResourceBundle.Control control)
Returns a resource bundle using the specified base name, target locale, class loader and control. |
static ResourceBundle |
getBundle(String baseName,
Locale targetLocale,
ResourceBundle.Control control)
Returns a resource bundle using the specified base name, target locale and control, and the caller's class loader. |
static ResourceBundle |
getBundle(String baseName,
ResourceBundle.Control control)
Returns a resource bundle using the specified base name, the default locale and the specified control. |
abstract Enumeration<String> |
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 Set<String> |
handleKeySet()
Returns a Set of the keys contained only
in this ResourceBundle . |
Set<String> |
keySet()
Returns a Set of all keys contained in this
ResourceBundle and its parent bundles. |
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 foundpublic static final ResourceBundle getBundle(String baseName, ResourceBundle.Control control)
getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader(), control),except that
getClassLoader()
is run with the security
privileges of ResourceBundle
. See getBundle
for the
complete description of the resource bundle loading process with a
ResourceBundle.Control
.
baseName
- the base name of the resource bundle, a fully qualified class
namecontrol
- the control which gives information for the resource bundle
loading process
NullPointerException
- if baseName
or control
is
null
MissingResourceException
- if no resource bundle for the specified base name can be found
IllegalArgumentException
- if the given control
doesn't perform properly
(e.g., control.getCandidateLocales
returns null.)
Note that validation of control
is performed as
needed.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 foundpublic static final ResourceBundle getBundle(String baseName, Locale targetLocale, ResourceBundle.Control control)
getBundle(baseName, targetLocale, this.getClass().getClassLoader(), control),except that
getClassLoader()
is run with the security
privileges of ResourceBundle
. See getBundle
for the
complete description of the resource bundle loading process with a
ResourceBundle.Control
.
baseName
- the base name of the resource bundle, a fully qualified
class nametargetLocale
- the locale for which a resource bundle is desiredcontrol
- the control which gives information for the resource
bundle loading process
Locale
in locales
NullPointerException
- if baseName
, locales
or
control
is null
MissingResourceException
- if no resource bundle for the specified base name in any
of the locales
can be found.
IllegalArgumentException
- if the given control
doesn't perform properly
(e.g., control.getCandidateLocales
returns null.)
Note that validation of control
is performed as
needed.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.
getBundle
caches instantiated resource bundles and
may return the same resource bundle instance multiple
times.
The baseName
argument should be a fully qualified class name. However, for
compatibility with earlier versions, Sun's Java SE 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.properties MyResources_fr.properties MyResources_fr_CH.class MyResources_fr_CH.properties MyResources_en.properties MyResources_es_ES.classThe 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: