Understanding Locale in Java
Locale in Java represents a specific geographical, political, or cultural region. It consists of language, country, and sometimes variant codes. Knowing how to correctly define a locale is essential for internationalizing your application.
Valid Locale Strings
A valid locale string follows the format language_country
, where language
is a lowercase ISO-639 code and country
is an uppercase ISO-3166-1 code. Optionally, a variant can be added.
Locale locale = new Locale("en", "US");
System.out.println(locale); // Output: en_US
Using Locale.Builder
Instead of directly using the Locale
constructor, Java provides Locale.Builder
, which allows you to set properties like language and country more flexibly.
Locale locale = new Locale.Builder()
.setLanguage("fr")
.setRegion("FR")
.build();
System.out.println(locale); // Output: fr_FR
Resource Bundles in Java
Java uses resource bundles to provide localized content based on the current locale. Resource bundles are collections of key-value pairs, where the keys are typically string identifiers, and the values are the localized content for a particular locale.
Using Resource Bundles
The ResourceBundle
class is used to load locale-specific data. When you call getBundle()
, Java looks for the appropriate resource bundle file based on the current locale.
ResourceBundle bundle = ResourceBundle.getBundle("MessagesBundle", locale);
System.out.println(bundle.getString("greeting")); // Output: Bonjour (if locale is fr_FR)
Fallback for Missing Keys
If a resource key is missing, the default behavior is to return null
. However, you can provide fallback values using the getProperty()
method.
ResourceBundle bundle = ResourceBundle.getBundle("MessagesBundle", locale);
System.out.println(bundle.getString("greeting")); // Output: null (if key is missing)
System.out.println(bundle.getProperty("unknownKey", "Default Value")); // Output: Default Value
Understanding Resource Bundle Hierarchy
Java follows a hierarchy when searching for resource bundles. It first looks for a bundle with both language and country, then it searches with just the language, and finally, it defaults to the base bundle if no match is found.
For instance, if you request a fr_FR
bundle, and it's not found, Java will attempt to load fr
and then fall back to the default base bundle.
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