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:
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().
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. Cache Management Resource bundle instances created by the 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. Example 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 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
static void clearCache()
static void clearCache(ClassLoader loader)
boolean containsKey(String key)
key is contained in this ResourceBundle or its parent bundles. static ResourceBundle getBundle(String baseName)
static ResourceBundle getBundle(String baseName, Locale locale)
static ResourceBundle getBundle(String baseName, Locale locale, ClassLoader loader)
static ResourceBundle getBundle(String baseName, Locale targetLocale, ClassLoader loader, ResourceBundle.Control control)
static ResourceBundle getBundle(String baseName, Locale targetLocale, ResourceBundle.Control control)
static ResourceBundle getBundle(String baseName, ResourceBundle.Control control)
abstract Enumeration<String> getKeys()
Locale getLocale()
Object getObject(String key)
String getString(String key)
String[] getStringArray(String key)
protected abstract Object handleGetObject(String key)
protected Set<String> handleKeySet()
Set of the keys contained only in this ResourceBundle. Set<String> keySet()
Set of all keys contained in this ResourceBundle and its parent bundles. protected void setParent(ResourceBundle parent)
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait parent
protected ResourceBundle parent
getObject when this bundle does not contain a particular resource.
public ResourceBundle()
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 string
public 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 array
public 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 found
public 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,
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 name
control - 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 name
locale - 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 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 name
targetLocale - the locale for which a resource bundle is desired
control - 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 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.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 shown locale argument values instantiates resource bundles from the following sources:
The file MyResources_fr_CH.properties is never used because it is hidden by 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 name
locale - the locale for which a resource bundle is desired
loader - 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 found
public 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. LocaleLocale("")), 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.MessagesLocale: 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_ITfoo/bar/Messages_it_IT.propertiesfoo.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 candiate 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 name
targetLocale - the locale for which a resource bundle is desired
loader - the class loader from which to load the resource bundle
control - the control which gives information for the resource bundle loading process
NullPointerException - if baseName, targetLocale, loader, 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 void clearCache()
ResourceBundle.Control.getTimeToLive(String,Locale)
public static final void clearCache(ClassLoader loader)
loader - the class loader
NullPointerException - if loader is null
ResourceBundle.Control.getTimeToLive(String,Locale)
protected abstract Object handleGetObject(String key)
key - the key for the desired object
NullPointerException - if key is null
public 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 key
true if the given key is contained in this ResourceBundle or its parent bundles; false otherwise.
NullPointerException - if key is null
public 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 the next calls. Override this method in subclass implementations for faster handling.
Set of the keys contained only in this ResourceBundle
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