Java Doc for ResourceBundle.java in  » 6.0-JDK-Core » Collections-Jar-Zip-Logging-regex » java » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

This allows you to write programs that can:

• be easily localized, or translated, into different languages
• handle multiple locales at once
• be easily modified later to support even more locales

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 ResourceBundle.getBundle(java.lang.String,java.util.Locale) 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
 };
 }
 }
 

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"));
 

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

Cache Management

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;
 }
 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"));
 }
 }
 

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 java.util.Locale.getDefault 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):

• baseName + "_" + language1 + "_" + country1 + "_" + variant1
• baseName + "_" + language1 + "_" + country1
• baseName + "_" + language1
• baseName + "_" + language2 + "_" + country2 + "_" + variant2
• baseName + "_" + language2 + "_" + country2
• baseName + "_" + language2
• baseName

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.

The default implementation returns a Set of the keys returned by the ResourceBundle.getKeys() getKeys method except for the ones for which the ResourceBundle.handleGetObject(String)handleGetObject method returns null.

getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader()),

 getBundle(baseName, Locale.getDefault(),
 this.getClass().getClassLoader(), control),
 

getBundle(baseName, locale, this.getClass().getClassLoader()),

 getBundle(baseName, targetLocale, this.getClass().getClassLoader(),
 control),
 

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 java.util.Locale.getDefault 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):

• baseName + "_" + language1 + "_" + country1 + "_" + variant1
• baseName + "_" + language1 + "_" + country1
• baseName + "_" + language1
• baseName + "_" + language2 + "_" + country2 + "_" + variant2
• baseName + "_" + language2 + "_" + country2
• baseName + "_" + language2
• baseName

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:

• First, it attempts to load a class using the candidate bundle name. If such a class can be found and loaded using the specified class loader, is assignment compatible with ResourceBundle, is accessible from ResourceBundle, and can be instantiated, getBundle creates a new instance of this class and uses it as the result resource bundle.
• Otherwise, 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 java.lang.ClassLoader.getResource(java.lang.String) 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 ResourceBundle.setParent(java.util.ResourceBundle) 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 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.
Parameters:
  baseName - the base name of the resource bundle, a fully qualified class name
Parameters:
  locale - the locale for which a resource bundle is desired
Parameters:
  loader - the class loader from which to load the resource bundle a resource bundle for the given base name and locale
exception:
  java.lang.NullPointerException - if baseName, locale, or loader is null
exception:
  MissingResourceException - if no resource bundle for the specified base name can be found
since:
   1.2

1. This factory method looks up the resource bundle in the cache for the specified 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.
2. The ResourceBundle.Control.getFormats(String)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 -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.
3. The ResourceBundle.Control.getCandidateLocales(StringLocale) control.getCandidateLocales method is called with the target locale to get a list of candidate Locales for which resource bundles are searched.
4. The ResourceBundle.Control.newBundle(StringLocaleStringClassLoaderboolean) 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

5. If the previous step has found no resource bundle, proceed to Step 6. If a bundle has been found that is a base bundle (a bundle for 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.
6. The ResourceBundle.Control.getFallbackLocale(StringLocale) 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.
7. At this point, we have found a resource bundle that's not the base bundle. If this bundle set its parent during its instantiation, it is returned to the caller. Otherwise, its parent chain is instantiated based on the list of candidate locales from which it was found. Finally, the bundle is returned to the caller.

During the resource bundle loading process above, this factory method looks up the cache before calling the Control.newBundle(StringLocaleStringClassLoaderboolean)control.newBundle method. If the time-to-live period of the resource bundle found in the cache has expired, the factory method calls the ResourceBundle.Control.needsReload(StringLocaleStringClassLoaderResourceBundlelong) 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(StringLocale)control.getTimeToLive for details.

The following is an example of the bundle loading process with the default ResourceBundle.Control implementation.

Conditions:

• Base bundle name: foo.bar.Messages
• Requested Locale: Locale.ITALY
• Default Locale: Locale.FRENCH
• Available resource bundles: foo/bar/Messages_fr.properties and foo/bar/Messages.properties

First, getBundle tries loading a resource bundle in the following sequence.

• class foo.bar.Messages_it_IT
• file foo/bar/Messages_it_IT.properties
• class foo.bar.Messages_it
• file foo/bar/Messages_it.properties
• class foo.bar.Messages
• file foo/bar/Messages.properties

At this point, getBundle finds foo/bar/Messages.properties, which is put on hold because it's the base bundle. getBundle calls Control.getFallbackLocale(StringLocale)control.getFallbackLocale("foo.bar.Messages", Locale.ITALY) which returns Locale.FRENCH. Next, getBundle tries loading a bundle in the following sequence.

• class foo.bar.Messages_fr
• file foo/bar/Messages_fr.properties
• class foo.bar.Messages
• file foo/bar/Messages.properties

getBundle 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.
Parameters:
  baseName - the base name of the resource bundle, a fully qualifiedclass name
Parameters:
  targetLocale - the locale for which a resource bundle is desired
Parameters:
  loader - the class loader from which to load the resource bundle
Parameters:
  control - the control which gives information for the resourcebundle loading process a resource bundle for the given base name and locale
exception:
  NullPointerException - if baseName, targetLocale,loader, or control isnull
exception:
  MissingResourceException - if no resource bundle for the specified base name can be found
exception:
  IllegalArgumentException - if the given control doesn't perform properly(e.g., control.getCandidateLocales returns null.) Note that validation of control is performed asneeded.
since:
   1.6

(String) ResourceBundle.getObject(java.lang.String) getObject (key).

(String[]) ResourceBundle.getObject(java.lang.String) getObject (key).

The default implementation returns a Set of the keys returned by the ResourceBundle.getKeys() getKeys method except for the ones for which the ResourceBundle.handleGetObject(String)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. a Set of the keys contained only in thisResourceBundle
since:
   1.6