How do you manage internationalization (i18n) in Spring applications?

Table of Contents

• Introduction
  • 1. Configuring Locale Resolver
    • Example: Configuring SessionLocaleResolver
  • 2. Configuring Message Source
    • Example: Configuring MessageSource
  • 3. Using Message Properties for Localization
    • Example: messages.properties
    • Example: messages_en.properties
    • Example: messages_fr.properties
  • 4. Accessing Messages in Controllers and Views
    • Example: Accessing Messages in a Controller
    • Example: Accessing Messages in Thymeleaf Template
  • 5. Changing Locale Dynamically
    • Example: Switching Locale via URL
• 6. Conclusion

Introduction

Internationalization (i18n) is the process of designing applications to be easily adaptable to different languages and regions without engineering changes. In Spring applications, managing i18n involves providing language-specific content, handling locale preferences, and using message resources to display text in different languages. Spring offers several ways to configure and manage i18n, allowing your application to support multiple languages and localizations effectively.

1. Configuring Locale Resolver

Spring provides a LocaleResolver to resolve the user's locale based on their preferences. The most common LocaleResolver is SessionLocaleResolver, which stores the locale in the user's session. Alternatively, you can use CookieLocaleResolver or AcceptHeaderLocaleResolver to resolve the locale based on cookies or HTTP headers.

Example: Configuring SessionLocaleResolver

In this configuration:

• The SessionLocaleResolver is set as the default LocaleResolver.
• The default locale is set to Locale.ENGLISH, but it can be customized based on user preferences.

2. Configuring Message Source

Spring uses message source files (properties files) to store localized messages. These files contain key-value pairs, where the key is used in the application, and the value is the translated message.

Example: Configuring MessageSource

In this configuration:

• The ReloadableResourceBundleMessageSource is used to load message properties from files located under classpath:messages.
• The UTF-8 encoding ensures that the messages are correctly displayed with special characters.
• Multiple files like messages.properties, messages_en.properties, messages_fr.properties can be used for different languages.

3. Using Message Properties for Localization

The message properties files contain the actual translations for the application. You can have a default messages.properties file and then language-specific files for each locale (e.g., messages_en.properties, messages_fr.properties).

Example: messages.properties

Example: messages_en.properties

Example: messages_fr.properties

4. Accessing Messages in Controllers and Views

You can access the localized messages in Spring controllers or views using the MessageSource bean or directly through the Spring tags in JSP or Thymeleaf templates.

Example: Accessing Messages in a Controller

In this controller:

• The welcome() method uses the MessageSource to fetch the localized message for welcome.message.
• The lang parameter determines the locale, and if it is not provided, it defaults to Locale.ENGLISH.

Example: Accessing Messages in Thymeleaf Template

In this Thymeleaf example:

• The #{welcome.message} syntax is used to display the message key's value from the messages.properties file, depending on the user's locale.

5. Changing Locale Dynamically

To allow users to change the locale dynamically, you can provide a mechanism to switch between locales (e.g., through a URL, session, or a dropdown menu in the UI).

Example: Switching Locale via URL

You can update the locale in the session based on user input, such as from a URL parameter.

In this example:

• The /changeLocale endpoint updates the locale based on the lang query parameter and stores it in the session.
• The SessionLocaleResolver updates the locale for subsequent requests.

6. Conclusion

Managing internationalization (i18n) in Spring applications allows your app to be adapted to different languages and regions efficiently. By configuring the LocaleResolver and MessageSource, Spring makes it easy to load and display localized messages based on the user’s locale.

Key steps for i18n in Spring include:

• Configuring a LocaleResolver to determine the user’s locale.
• Setting up MessageSource to load and serve message properties.
• Using messages in controllers and views with MessageSource or Spring tags.
• Dynamically changing the locale to cater to user preferences.

With these tools, Spring simplifies the process of building multilingual applications and ensures a seamless experience for users worldwide.