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Trail: Internationalization
Lesson: Isolating Locale-Specific Data
Isolating Locale-Specific Data
About the ResourceBundle Class
Preparing to Use a ResourceBundle
Backing a ResourceBundle with Properties Files
Using a ListResourceBundle
Customizing Resource Bundle Loading
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Customizing Resource Bundle Loading

> 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 `ResourceBundel.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.

> ### 1. Create the `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 Chineese
> - ``RBControl_zh_cn.properties`` – Region only: China
> - ``RBControl_zh_hk.properties`` – Region only: Hong Kong
> - ``RBControl_zh_tw.properties`` – Taiwan

> In this example an application creates a new locale for the Hong Kong region.

> ### 2. Create a `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.

> ### 3. Invoke the `getCandidateLocales` method

> The `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&rt; 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.

> ### 4. Call the `test` class

> Call 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);
>         }

> ### 5. Run the Sample Program

> 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.

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