Earlier in this lesson you have learned how to create and access objects of the ResourceBundle
class. This section extents your knowledge and explains how to take an advantage from the
ResourceBundle.Control
class capabilities.
The ResourceBundle.Control
was created to specify how to locate and instantiate resource bundles. It defines a set of callback methods that are invoked by the
ResourceBundle.getBundle
factory methods during the bundle loading process.
Unlike a
ResourceBundle.getBundle
method described earlier, this ResourceBundle.getBundle
method defines a resource bundle using the specified base name, the default locale and the specified control.
public static final ResourceBundle getBundle( String baseName, ResourceBundle.Control cont // ...
The specified control provide information for the resource bundle loading process.
The following sample program called
RBControl.java
illustrates how to define your own search paths for Chinese locales.
properties
Files.As it was described before you can load your resources either from classes or from properties
files. These files contain descriptions for the following locales:
RBControl.properties
Global
RBControl_zh.properties
Language only: Simplified Chinese
RBControl_zh_cn.properties
Region only: China
RBControl_zh_hk.properties
Region only: Hong Kong
RBControl_zh_tw.properties
TaiwanIn this example an application creates a new locale for the Hong Kong region.
ResourceBundle
instance.As in the example in the previous section, this application creates a ResourceBundle
instance by invoking the getBundle
method:
private static void test(Locale locale) { ResourceBundle rb = ResourceBundle.getBundle( "RBControl", locale, new ResourceBundle.Control() { // ...
The getBundle
method searches for properties
files with the RBControl prefix. However, this method contains a Control
parameter, which drives the process of searching the Chineese locales.
getCandidateLocales
methodThe getCandidateLocales
method returns a list of the Locales
objects as candidate locales for the base name and locale.
new ResourceBundle.Control() { @Override public List<Locale> getCandidateLocales( String baseName, Locale locale) { // ...
The default implementation returns a list of the Locale
objects as follows: Locale(language, country).
However, this method is overriden to implement the following specific behavior:
if (baseName == null) throw new NullPointerException(); if (locale.equals(new Locale("zh", "HK"))) { return Arrays.asList( locale, Locale.TAIWAN, // no Locale.CHINESE here Locale.ROOT); } else if (locale.equals(Locale.TAIWAN)) { return Arrays.asList( locale, // no Locale.CHINESE here Locale.ROOT); }
Note, that the last element of the sequence of candidate locales must be a root locale.
test
classCall the test
class for the following four different locales:
public static void main(String[] args) { test(Locale.CHINA); test(new Locale("zh", "HK")); test(Locale.TAIWAN); test(Locale.CANADA); }
You will see the program output as follows:
locale: zh_CN region: China language: Simplified Chinese locale: zh_HK region: Hong Kong language: Traditional Chinese locale: zh_TW region: Taiwan language: Traditional Chinese locale: en_CA region: global language: English
Note that the newly created was assigned the Hong Kong region, because it was specified in an appropriate properties
file. Traditional Chinese was assigned as the language for the Taiwan locale.
Two other interesting methods of the ResourceBundle.Control
class were not used in the RBControl
example, but they deserved to be mentioned. The getTimeToLive
method is used to determine how long the resource bundle can exist in the cache. If the time limit for a resource bundle in the cache has expired, the needsReload
method is invoked to determine whether the resource bundle needs to be reloaded.