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FlexDoc/Javadoc 2.0 Demo Java Doc |
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 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.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 }; } }
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 a MissingResourceException.button1 = new Button(myResources.getString("OkKey")); button2 = new Button(myResources.getString("CancelKey"));
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.
A resource bundle provider can provide resource bundles in any format such XML which replaces the need of ResourceBundle.Control.
The getBundle factory methods with no Control parameter locate and load resource bundles from service providers. It may continue the search as if calling Module.getResourceAsStream(String) to find the named resource from a given module and calling ClassLoader.getResourceAsStream(String); refer to the specification of the getBundle method for details. Only non-encapsulated resource bundles of "java.class" or "java.properties" format are searched.
If the caller module is a resource bundle provider, it does not fall back to the class loader search.
ResourceBundle.Control is designed for an application deployed in an unnamed module, for example to support resource bundles in non-standard formats or package localized resources in a non-traditional convention. ResourceBundleProvider is the replacement for ResourceBundle.Control when migrating to modules. UnsupportedOperationException will be thrown when a factory method that takes the ResourceBundle.Control parameter is called.
For the getBundle factory methods that take no ResourceBundle.Control instance, their default behavior of resource bundle loading can be modified with custom ResourceBundleControlProvider implementations. 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 for supporting the same base name, the first one returned from ServiceLoader will be used. A custom ResourceBundle.Control implementation is ignored by named modules.
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.// 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")); } }
Nested Class Summary |
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static class |
ResourceBundle.Control defines a set of callback methods
that are invoked by the ResourceBundle.getBundle factory
methods during the bundle loading process.
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Field Summary |
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protected ResourceBundle |
The parent bundle of this bundle.
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Constructor Summary |
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Sole constructor.
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Method Summary |
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static final void |
Removes all resource bundles from the cache that have been loaded
by the caller's module.
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static final void |
clearCache(ClassLoader loader)
Removes all resource bundles from the cache that have been loaded
by the given class loader.
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boolean |
containsKey(String key)
Determines whether the given key is contained in
this ResourceBundle or its parent bundles.
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Returns the base name of this bundle, if known, or null if unknown.
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static final ResourceBundle |
Gets a resource bundle using the specified base name, the default locale,
and the caller module.
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static final ResourceBundle |
Gets a resource bundle using the specified base name and locale,
and the caller module.
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static ResourceBundle |
Gets a resource bundle using the specified base name, locale, and class
loader.
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static ResourceBundle |
Returns a resource bundle using the specified base name, target
locale, class loader and control.
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static ResourceBundle |
Gets a resource bundle using the specified base name and locale
on behalf of the specified module.
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static final ResourceBundle |
Returns a resource bundle using the specified base name, target
locale and control, and the caller's class loader.
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static ResourceBundle |
Gets a resource bundle using the specified base name and the default locale
on behalf of the specified module.
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static final ResourceBundle |
Returns a resource bundle using the specified base name, the
default locale and the specified control.
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abstract Enumeration<String> |
getKeys()
Returns an enumeration of the keys.
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Returns the locale of this resource bundle.
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final Object |
Gets an object for the given key from this resource bundle or one of its parents.
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final String |
Gets a string for the given key from this resource bundle or one of its parents.
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final String[] |
getStringArray(String key)
Gets a string array for the given key from this resource bundle or one of its parents.
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protected abstract Object |
handleGetObject(String key)
Gets an object for the given key from this resource bundle.
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Returns a Set of the keys contained only
in this ResourceBundle.
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keySet()
Returns a Set of all keys contained in this
ResourceBundle and its parent bundles.
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protected void |
setParent(ResourceBundle parent)
Sets the parent bundle of this bundle.
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Methods inherited from class java.lang.Object |
public ResourceBundle |
() |
public String getBaseBundleName |
() |
public final String getString |
(String key) |
(String) getObject(key)
.
public final String[] getStringArray |
(String key) |
(String[]) getObject(key)
.
public final Object getObject |
(String key) |
public Locale getLocale |
() |
protected void setParent |
(ResourceBundle parent) |
public static final ResourceBundle getBundle |
(String baseName) |
getBundle(baseName, Locale.getDefault(), callerModule),
public static final ResourceBundle getBundle |
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.
public static final ResourceBundle getBundle |
getBundle(baseName, locale, callerModule),
public static ResourceBundle getBundle |
getBundle(baseName, Locale.getDefault(), module)
public static ResourceBundle getBundle |
Resource bundles in named modules may be encapsulated. When the resource bundle is loaded from a service provider, the caller module must have an appropriate uses clause in its module descriptor to declare that the module uses of ResourceBundleProvider for the named resource bundle. Otherwise, it will load the resource bundles that are local in the given module as if calling Module.getResourceAsStream(String) or that are visible to the class loader of the given module as if calling ClassLoader.getResourceAsStream(String). When the resource bundle is loaded from the specified module, it is subject to the encapsulation rules specified by Module.getResourceAsStream.
If the given module is an unnamed module, then this method is equivalent to calling getBundle(baseName, targetLocale, module.getClassLoader() to load resource bundles that are visible to the class loader of the given unnamed module. Custom ResourceBundleControlProvider implementations, if present, will only be invoked if the specified module is an unnamed module.
public static final ResourceBundle getBundle |
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.
public static ResourceBundle getBundle |
When this method is called from a named module and the given loader is the class loader of the caller module, this is equivalent to calling:
otherwise, this is equivalent to calling:getBundle(baseName, targetLocale, callerModule)
where control is the default instance of ResourceBundle.Control unless a Control instance is provided by ResourceBundleControlProvider SPI. Refer to the description of modifying the default behavior. The following describes the default behavior.getBundle(baseName, targetLocale, loader, control)
Resource Bundle Search and Loading Strategy
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_deIn 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 some Locales, 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 of getCandidateLocales for 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:
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 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, 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:
Calling getBundle with the locale arguments below will instantiate resource bundles as follows:
Locale | Resource bundle |
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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.
public static ResourceBundle getBundle |
Index | Locale | format |
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1 | Locale("de", "DE") | java.class |
2 | Locale("de", "DE") | java.properties |
3 | Locale("de") | java.class |
4 | Locale("de") | java.properties |
5 | Locale("") | java.class |
6 | Locale("") | java.properties |
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:
First, getBundle tries loading a resource bundle in the following sequence.
At 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.
getBundle 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.
public static final void clearCache |
() |
public static final void clearCache |
(ClassLoader loader) |
protected abstract Object handleGetObject |
(String key) |
() |
public boolean containsKey |
(String key) |
() |
() |
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.
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FlexDoc/Javadoc 2.0 Demo Java Doc |