public abstract class ResourceBundle extends Object
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 {
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
};
}
}
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 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 implementation of a ResourceBundle subclass must be thread-safe
if it's simultaneously used by multiple threads. The default implementations
of the non-abstract methods in this class, and the methods in the direct
known concrete subclasses ListResourceBundle and
PropertyResourceBundle are thread-safe.
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.
For the getBundle factory
methods that take no ResourceBundle.Control instance, their default behavior of resource bundle loading
can be modified with installed ResourceBundleControlProvider implementations. Any installed providers are
detected at the ResourceBundle class loading time. If any of the
providers provides a ResourceBundle.Control for the given base name, that ResourceBundle.Control will be used instead of the default ResourceBundle.Control. If there is
more than one service provider installed for supporting the same base name,
the first one returned from ServiceLoader will be used.
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).
// 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"));
}
}
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| Modifier and Type | Class and Description |
|---|---|
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. |
| Modifier and Type | Field and Description |
|---|---|
protected ResourceBundle |
parent
The parent bundle of this bundle.
|
| Constructor and Description |
|---|
ResourceBundle()
Sole constructor.
|
| Modifier and Type | Method and Description |
|---|---|
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. |
String |
getBaseBundleName()
Returns the base name of this bundle, if known, or
null if unknown. |
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.
|
protected ResourceBundle parent
getObject
when this bundle does not contain a particular resource.public ResourceBundle()
public String getBaseBundleName()
null if unknown.
If not null, then this is the value of the baseName parameter
that was passed to the ResourceBundle.getBundle(...) method
when the resource bundle was loaded.ResourceBundle.getBundle(...) methods.getBundle(java.lang.String, java.util.Locale, java.lang.ClassLoader)public final String getString(String key)
(String) getObject(key).
key - the key for the desired stringNullPointerException - if key is nullMissingResourceException - if no object for the given key can be foundClassCastException - 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 arrayNullPointerException - if key is nullMissingResourceException - if no object for the given key can be foundClassCastException - 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 objectNullPointerException - if key is nullMissingResourceException - 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 nameNullPointerException - if baseName is nullMissingResourceException - 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 processNullPointerException - if baseName or control is
nullMissingResourceException - if no resource bundle for the specified base name can be foundIllegalArgumentException - 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 desiredNullPointerException - if baseName or locale is nullMissingResourceException - 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 processLocale in localesNullPointerException - if baseName, locales or
control is nullMissingResourceException - 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)
This method behaves the same as calling
getBundle(String, Locale, ClassLoader, Control) passing a
default instance of ResourceBundle.Control unless another ResourceBundle.Control is
provided with the ResourceBundleControlProvider SPI. Refer to the
description of modifying the default
behavior.
The following describes the default behavior.
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, script, country, and variant are all empty strings,
then the base name is the only candidate bundle name. Otherwise, a list
of candidate locales is generated from the attribute values of the
specified locale (language, script, country and variant) and appended to
the base name. Typically, this will look like the following:
baseName + "_" + language + "_" + script + "_" + country + "_" + variant
baseName + "_" + language + "_" + script + "_" + country
baseName + "_" + language + "_" + script
baseName + "_" + language + "_" + country + "_" + variant
baseName + "_" + language + "_" + country
baseName + "_" + language
Candidate bundle names where the final component is an empty string are omitted, along with the underscore. For example, if country is an empty string, the second and the fifth candidate bundle names above would be omitted. Also, if script is an empty string, the candidate names including script are omitted. For example, a locale with language "de" and variant "JAVA" will produce candidate names with base name "MyResource" below.
MyResource_de__JAVA
MyResource_de
In the case that the variant contains one or more underscores ('_'), a
sequence of bundle names generated by truncating the last underscore and
the part following it is inserted after a candidate bundle name with the
original variant. For example, for a locale with language "en", script
"Latn, country "US" and variant "WINDOWS_VISTA", and bundle base name
"MyResource", the list of candidate bundle names below is generated:
MyResource_en_Latn_US_WINDOWS_VISTA MyResource_en_Latn_US_WINDOWS MyResource_en_Latn_US MyResource_en_Latn MyResource_en_US_WINDOWS_VISTA MyResource_en_US_WINDOWS MyResource_en_US MyResource_en
Note: For someLocales, the list of candidate bundle names contains extra names, or the order of bundle names is slightly modified. See the description of the default implementation ofgetCandidateLocalesfor details.
getBundle then iterates over the candidate bundle names
to find the first one for which it can instantiate an actual
resource bundle. It uses the default controls' getFormats method, which generates two bundle names for each generated
name, the first a class name and the second a properties file name. 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 using the generated properties file name. 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. This continues until a result resource bundle is instantiated or the
list of candidate bundle names is exhausted. If no matching resource
bundle is found, the default control's getFallbackLocale method is called, which returns the current default
locale. A new sequence of candidate locale names is generated using this
locale and and searched again, as above.
If still no result bundle is found, the base name alone is looked up. If
this still fails, a MissingResourceException is thrown.
Once a result resource bundle has been found, its parent chain is instantiated. If the result bundle already has a parent (perhaps because it was returned from a cache) the chain is complete.
Otherwise, getBundle examines the remainder of the
candidate locale list that was used during the pass that generated the
result resource bundle. (As before, candidate bundle names where the
final component is an empty string are omitted.) When it comes to the
end of the candidate list, it tries the plain bundle name. With each of the
candidate bundle names it attempts to instantiate a resource bundle (first
looking for a class and then a properties file, as described above).
Whenever it succeeds, it calls the previously instantiated resource
bundle's setParent method
with the new resource bundle. This continues until the list of names
is exhausted or the current bundle already has a non-null parent.
Once the parent chain is complete, the bundle is returned.
Note: getBundle caches instantiated resource
bundles and might return the same resource bundle instance multiple times.
Note: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 PropertyResourceBundles by specifying a
path name (using "/") instead of a fully qualified class name (using
".").
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.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 locale arguments below will
instantiate resource bundles as follows:
| Locale("fr", "CH") | MyResources_fr_CH.class, parent MyResources_fr.properties, parent MyResources.class |
| Locale("fr", "FR") | MyResources_fr.properties, parent MyResources.class |
| Locale("de", "DE") | MyResources_en.properties, parent MyResources.class |
| Locale("en", "US") | MyResources_en.properties, parent MyResources.class |
| Locale("es", "ES") | MyResources_es_ES.class, parent MyResources.class |
The file MyResources_fr_CH.properties is never used because it is hidden by the MyResources_fr_CH.class. Likewise, MyResources.properties is also hidden by MyResources.class.
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 bundleNullPointerException - if baseName, locale, or loader is nullMissingResourceException - if no resource bundle for the specified base name can be foundpublic static ResourceBundle getBundle(String baseName, Locale targetLocale, ClassLoader loader, ResourceBundle.Control control)
getBundle
factory methods with no control argument, the given
control specifies how to locate and instantiate resource
bundles. Conceptually, the bundle loading process with the given
control is performed in the following steps.
baseName, targetLocale and
loader. If the requested resource bundle instance is
found in the cache and the time-to-live periods of the instance and
all of its parent instances have not expired, the instance is returned
to the caller. Otherwise, this factory method proceeds with the
loading process below.control.getFormats method is called to get resource bundle formats
to produce bundle or resource names. The strings
"java.class" and "java.properties"
designate class-based and property-based resource bundles, respectively. Other strings
starting with "java." are reserved for future extensions
and must not be used for application-defined formats. Other strings
designate application-defined formats.control.getCandidateLocales method is called with the target
locale to get a list of candidate Locales for
which resource bundles are searched.control.newBundle method is called to
instantiate a ResourceBundle for the base bundle name, a
candidate locale, and a format. (Refer to the note on the cache
lookup below.) This step is iterated over all combinations of the
candidate locales and formats until the newBundle method
returns a ResourceBundle instance or the iteration has
used up all the combinations. For example, if the candidate locales
are Locale("de", "DE"), Locale("de") and
Locale("") and the formats are "java.class"
and "java.properties", then the following is the
sequence of locale-format combinations to be used to call
control.newBundle.
Locale |
format |
Locale("de", "DE") |
java.class |
Locale("de", "DE") |
java.properties |
Locale("de") |
java.class |
Locale("de") |
java.properties |
Locale("") |
java.class |
Locale("") |
java.properties |
Locale("")), and the candidate locale list only contained
Locale(""), return the bundle to the caller. If a bundle
has been found that is a base bundle, but the candidate locale list
contained locales other than Locale(""), put the bundle on hold and
proceed to Step 6. If a bundle has been found that is not a base
bundle, proceed to Step 7.control.getFallbackLocale method is called to get a fallback
locale (alternative to the current target locale) to try further
finding a resource bundle. If the method returns a non-null locale,
it becomes the next target locale and the loading process starts over
from Step 3. Otherwise, if a base bundle was found and put on hold in
a previous Step 5, it is returned to the caller now. Otherwise, a
MissingResourceException is thrown.During the resource bundle loading process above, this factory
method looks up the cache before calling the control.newBundle method. If the time-to-live period of the
resource bundle found in the cache has expired, the factory method
calls the control.needsReload
method to determine whether the resource bundle needs to be reloaded.
If reloading is required, the factory method calls
control.newBundle to reload the resource bundle. If
control.newBundle returns null, the factory
method puts a dummy resource bundle in the cache as a mark of
nonexistent resource bundles in order to avoid lookup overhead for
subsequent requests. Such dummy resource bundles are under the same
expiration control as specified by control.
All resource bundles loaded are cached by default. Refer to
control.getTimeToLive for details.
The following is an example of the bundle loading process with the
default ResourceBundle.Control implementation.
Conditions:
foo.bar.Messages
Locale: Locale.ITALYLocale: Locale.FRENCHfoo/bar/Messages_fr.properties and
foo/bar/Messages.propertiesFirst, getBundle tries loading a resource bundle in
the following sequence.
foo.bar.Messages_it_IT
foo/bar/Messages_it_IT.properties
foo.bar.Messages_itfoo/bar/Messages_it.propertiesfoo.bar.Messagesfoo/bar/Messages.propertiesAt this point, getBundle finds
foo/bar/Messages.properties, which is put on hold
because it's the base bundle. getBundle calls control.getFallbackLocale("foo.bar.Messages", Locale.ITALY) which
returns Locale.FRENCH. Next, getBundle
tries loading a bundle in the following sequence.
foo.bar.Messages_frfoo/bar/Messages_fr.propertiesfoo.bar.Messagesfoo/bar/Messages.propertiesgetBundle finds
foo/bar/Messages_fr.properties and creates a
ResourceBundle instance. Then, getBundle
sets up its parent chain from the list of the candidate locales. Only
foo/bar/Messages.properties is found in the list and
getBundle creates a ResourceBundle instance
that becomes the parent of the instance for
foo/bar/Messages_fr.properties.
baseName - the base name of the resource bundle, a fully qualified
class nametargetLocale - the locale for which a resource bundle is desiredloader - the class loader from which to load the resource bundlecontrol - the control which gives information for the resource
bundle loading processNullPointerException - if baseName, targetLocale,
loader, or control is
nullMissingResourceException - if no resource bundle for the specified base name can be foundIllegalArgumentException - 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 void clearCache()
ResourceBundle.Control.getTimeToLive(String,Locale)public static final void clearCache(ClassLoader loader)
loader - the class loaderNullPointerException - if loader is nullResourceBundle.Control.getTimeToLive(String,Locale)protected abstract Object handleGetObject(String key)
key - the key for the desired objectNullPointerException - if key is nullpublic abstract Enumeration<String> getKeys()
Enumeration of the keys contained in
this ResourceBundle and its parent bundles.public boolean containsKey(String key)
key is contained in
this ResourceBundle or its parent bundles.key - the resource keytrue if the given key is
contained in this ResourceBundle or its
parent bundles; false otherwise.NullPointerException - if key is nullpublic Set<String> keySet()
Set of all keys contained in this
ResourceBundle and its parent bundles.Set of all keys contained in this
ResourceBundle and its parent bundles.protected Set<String> handleKeySet()
Set of the keys contained only
in this ResourceBundle.
The default implementation returns a Set of the
keys returned by the getKeys method except
for the ones for which the handleGetObject method returns null. Once the
Set has been created, the value is kept in this
ResourceBundle in order to avoid producing the
same Set in subsequent calls. Subclasses can
override this method for faster handling.
Set of the keys contained only in this
ResourceBundle Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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