Internationalization of Spring Boot RESTful Services

If your application serves a wide range of clients spanning across the globe, it becomes essential to be able to respond based on country and language of the origin of request. Internationalization is the processes of designing your application to be capable of the same. During the course of this article we will create a simple Spring Boot App with a single endpoint that can serve the same text in various languages.

Code Structure

spring-boot-i18n
│   .gitignore
│   HELP.md
│   mvnw
│   mvnw.cmd
│   pom.xml
│
└───src
    ├───main
    │   ├───java
    │   │   └───com
    │   │       └───techgoons
    │   │           └───i18n
    │   │                   I18nController.java
    │   │                   SpringBootI18nApplication.java
    │   │
    │   └───resources
    │           application.properties
    │           messages.properties
    │           messages_de.properties
    │           messages_es.properties
    │           messages_fr.properties
    │           messages_nl.properties
    │
    └───test
        └───java
            └───com
                └───techgoons
                    └───i18n
                            SpringBootI18nApplicationTests.java

You can use the spring boot initializer to generate the template with spring-boot-starter-web dependency.

How to enable i18n messaging in a spring boot app?

Update the application.properties as below. Explanation for each configuration has been added as comments

Resource Bundles

As specified in the application.properties, application will look for messages*.properties named files for fetching content.

messages.properties — the default file will contain English key value pairs

welcome=Welcome to Tech Goons homepage

messages_de.properties — German

welcome=Willkommen auf der Tech Goons-Homepage

messages_es.properties — Spanish

welcome=Bienvenido a la página de inicio de Tech Goons

messages_fr.properties — French

welcome=Bienvenue sur la page d'accueil de Tech Goons

messages_nl.properties — Dutch

welcome=Welkom op de startpagina van Tech Goons

All translations have been generated using Google translate. Apologies in advance if certain translations are not correct.

Rest Controller

We will keep the controller simple and expose just a single endpoint that will fetch the welcome message from resource bundle based on Accept-Language header in the request.

We autowire the MessageSource component which has the necessary means to fetch values from appropriate resource bundle based on language details passed in request header.

Testing!

After starting the server you can try out below cURL commands.

curl --location --request GET 'localhost:8080/' --header 'Accept-Language: de'
OUTPUT: Willkommen auf der Tech Goons-Homepage
curl --location --request GET 'localhost:8080/' --header 'Accept-Language: es'
OUTPUT: Bienvenido a la p�gina de inicio de Tech Goons

Source code here. Happy Learning!