Java Doc for ResourceBundle.java in  » 6.0-JDK-Modules » j2me » 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 {
 public Object[][] getContents() {
 return contents;
 }
 static final Object[][] contents = {
 // LOCALIZE THIS
 {"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 2 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 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 Hashtable). 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).

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;
 }
 }
 // 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;
 }
 }
 

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.

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

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

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.

Implementations of getBundle may cache instantiated resource bundles and return the same resource bundle instance multiple times. They may also vary the sequence in which resource bundles are instantiated as long as the selection of the result resource bundle and its parent chain are compatible with the description above.

The baseName argument should be a fully qualified class name. However, for compatibility with earlier versions, Sun's Java 2 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_fr_CH.properties, MyResources_fr_CH.class, MyResources_fr.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:

• Locale("fr", "CH"): result MyResources_fr_CH.class, parent MyResources_fr.properties, parent MyResources.class
• Locale("fr", "FR"): result MyResources_fr.properties, parent MyResources.class
• Locale("de", "DE"): result MyResources_en.properties, parent MyResources.class
• Locale("en", "US"): result MyResources_en.properties, parent MyResources.class
• Locale("es", "ES"): result MyResources_es_ES.class, parent 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
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 a resource bundle for the given base name and locale
since:
   1.2

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

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