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Java Locale, Localization API, and Internationalization with ResourceBundle

1. Introduction

When developing applications for global audiences, it's essential to adapt them to various languages and regions. Java provides several classes and APIs for internationalization (i18n) and localization (l10n), allowing your application to present itself appropriately based on the user's locale.

2. Understanding Locale

The Locale class represents a specific geographical, political, or cultural region. The most common use of Locale is to define the language and region in which the program should operate.

Creating a Locale

The Locale class provides several ways to create a Locale object:

  • Using Language Code

    Locale locale = new Locale("en"); // English

  • Using Language and Country Code

    Locale locale = new Locale("en", "US"); // English (United States)
Locale localeFR = new Locale("fr", "FR"); // French (France)

  • Using predefined constants

    Locale localeCanada = Locale.CANADA;
Locale localeJapan = Locale.JAPAN;

Getting Locale Information

Locale locale = new Locale("fr", "FR");
System.out.println("Language: " + locale.getLanguage()); // Output: fr
System.out.println("Country: " + locale.getCountry());   // Output: FR

3. Localization API

Java provides several tools to help developers localize their applications. The Locale class, combined with classes like NumberFormat, DateFormat, and ResourceBundle, allows developers to tailor their application's output to a particular locale.

Number Formatting

Java provides NumberFormat for formatting numbers according to a specific locale:

double number = 12345.67;
NumberFormat nf = NumberFormat.getInstance(Locale.FRANCE);
String formattedNumber = nf.format(number); // 12 345,67 in French
System.out.println(formattedNumber);

Date Formatting with LocalDateTime

You can format dates using DateTimeFormatter with LocalDateTime:

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class DateFormattingExample {
    public static void main(String[] args) {
        LocalDateTime now = LocalDateTime.now();
        
        DateTimeFormatter germanFormatter = DateTimeFormatter.ofPattern("dd MMMM yyyy, HH:mm", Locale.GERMANY);
        String formattedDateGermany = now.format(germanFormatter);
        
        System.out.println("Formatted Date (Germany): " + formattedDateGermany);
    }
}

4. Internationalization with ResourceBundle

The ResourceBundle class allows you to define locale-specific resources, such as text strings, that can be dynamically loaded based on the user's locale.

Setting up Resource Bundles

  1. Create a properties file for each locale. For example, for English and French, create the following files:

  • messages_en_US.properties:

    greeting = Hello
farewell = Goodbye

  • messages_fr_FR.properties:

    greeting = Bonjour
farewell = Au revoir

  1. Access Resource Bundles in Java:

    import java.util.Locale;
import java.util.ResourceBundle;

public class LocalizationExample {
    public static void main(String[] args) {
        Locale enLocale = new Locale("en", "US");
        Locale frLocale = new Locale("fr", "FR");

        ResourceBundle bundleEn = ResourceBundle.getBundle("messages", enLocale);
        ResourceBundle bundleFr = ResourceBundle.getBundle("messages", frLocale);

        System.out.println("English Greeting: " + bundleEn.getString("greeting"));
        System.out.println("French Greeting: " + bundleFr.getString("greeting"));
    }
}

    Output:

    English Greeting: Hello
French Greeting: Bonjour

ResourceBundle Fallback Mechanism

If a specific locale resource bundle is not found, Java falls back to the default resource bundle.

For example, if you request a bundle for "es_ES" (Spanish), and no "messages_es_ES.properties" exists, it will fall back to the default "messages.properties" file.

5. Locale-Specific Resource Handling Example

Let's create a complete example that uses the Locale, ResourceBundle, and NumberFormat for localization.

import java.text.NumberFormat;
import java.util.Locale;
import java.util.ResourceBundle;

public class InternationalizationDemo {

    public static void main(String[] args) {
        // Define different locales
        Locale usLocale = new Locale("en", "US");
        Locale franceLocale = new Locale("fr", "FR");

        // Get the resource bundles for each locale
        ResourceBundle usBundle = ResourceBundle.getBundle("messages", usLocale);
        ResourceBundle frBundle = ResourceBundle.getBundle("messages", franceLocale);

        // Retrieve localized messages
        System.out.println(usLocale.getDisplayLanguage() + " greeting: " + usBundle.getString("greeting"));
        System.out.println(franceLocale.getDisplayLanguage() + " greeting: " + frBundle.getString("greeting"));

        // Formatting numbers in different locales
        double price = 12345.67;
        NumberFormat usCurrencyFormat = NumberFormat.getCurrencyInstance(usLocale);
        NumberFormat frCurrencyFormat = NumberFormat.getCurrencyInstance(franceLocale);

        System.out.println("Price in US: " + usCurrencyFormat.format(price));
        System.out.println("Price in France: " + frCurrencyFormat.format(price));
    }
}

  • messages_en_US.properties:

    greeting = Hello

  • messages_fr_FR.properties:

    greeting = Bonjour

  • Output:

    English greeting: Hello
French greeting: Bonjour
Price in US: $12,345.67
Price in France: 12 345,67 €

6. Conclusion

Java’s Locale, ResourceBundle, and formatting classes provide robust support for creating internationalized applications. By using these tools, you can easily customize your application’s behavior for different languages, countries, and regions.