How do you configure message properties for localization?

Table of Contents

• Introduction
  • Steps to Configure Message Properties for Localization
    • 1. Create Message Property Files
    • 2. Configure the **MessageSource** Bean in Spring Boot
    • 3. Enable Locale Resolution
    • 4. Use Localized Messages in Views and Controllers
    • 5. Change Locale Dynamically
• Conclusion

Introduction

Localization (l10n) is the process of adapting your application for different languages or regions, allowing you to display content in the user's preferred language. Spring Boot provides powerful support for internationalization (i18n), and a key part of this process is the MessageSource interface. This interface enables the retrieval of localized messages from properties files based on the user's locale. In this guide, we will walk through how to configure message properties for localization in Spring Boot.

Steps to Configure Message Properties for Localization

1. Create Message Property Files

The first step in enabling localization in Spring Boot is to create message properties files. These files will store the localized messages that will be displayed to the user based on their locale.

• The default file messages.properties will contain default (e.g., English) messages.
• Additional files like messages_fr.properties for French, messages_es.properties for Spanish, and so on, will contain translations for other languages.

Example: **messages.properties** (English - default)

Example: **messages_fr.properties** (French)

Example: **messages_es.properties** (Spanish)

Each of these files contains the same keys but with translations specific to the respective language.

2. Configure the **MessageSource** Bean in Spring Boot

In Spring Boot, you need to configure a MessageSource bean that loads the messages from your property files. This can be done by defining a MessageSource bean in your configuration class.

Java Configuration Example:

In this configuration:

• setBasename("classpath:messages") tells Spring Boot to look for message files with the base name messages (e.g., messages.properties, messages_fr.properties, etc.) in the classpath.
• setDefaultEncoding("UTF-8") ensures that character encoding is set to UTF-8 for international characters.
• setCacheSeconds(3600) configures the caching of message files for one hour, so Spring Boot does not need to reload them on every request.

3. Enable Locale Resolution

To use different locales in your application, you need to tell Spring Boot how to resolve the user's locale based on their preferences (e.g., browser settings, session, or request parameters). This is done using the LocaleResolver.

Configuration Example:

In this example:

• AcceptHeaderLocaleResolver is used to resolve the locale from the Accept-Language header sent by the client (e.g., browser).
• The LocaleChangeInterceptor intercepts incoming requests and allows the locale to be changed based on a request parameter, such as ?lang=fr for French or ?lang=es for Spanish.

4. Use Localized Messages in Views and Controllers

Once your message properties and locale resolution are configured, you can use the MessageSource in your controllers and views to retrieve localized messages.

Controller Example:

In this example:

• The getMessage() method of the MessageSource interface retrieves the localized greeting message based on the user's locale.
• If the user's locale is French, the message will be fetched from messages_fr.properties. If it's Spanish, it will be fetched from messages_es.properties.

Thymeleaf Template Example (greeting.html):

5. Change Locale Dynamically

You can provide a way for users to change the locale by clicking a link or setting the lang parameter in the URL. For example, you can create links that switch between languages:

Thymeleaf Template Example (language-selector.html):

By clicking these links, the locale is changed dynamically, and Spring Boot will load the appropriate messages for the selected language.

Conclusion

Configuring message properties for localization in Spring Boot allows your application to support multiple languages and regions. By using the MessageSource interface and message bundles (property files), you can centralize your application's messages and easily serve them based on the user's locale. The LocaleResolver and LocaleChangeInterceptor help ensure that users get the right language, and you can easily retrieve localized messages in both controllers and views. This makes your application more accessible and adaptable to a global audience.