Spring Boot Internationalization

In this technical post, we will see how to manage different languages at your Spring Boot application aka. internationalization. NOTE: If you need to know what tools you need to have installed in your computer in order to create a Spring Boot basic project, please refer my previous post: Spring Boot. Spring Boot uses MessageSource configured with a MessageSourceAutoConfiguration. These settings can be easily changed in the application.properties file:


Once we create that line, you can define your application messages in the file resources/i18n/messages.properties:

user.hello=Hello from internationalization!

Spring boot create a MessageSource bean and is automatically added to the context, so you can use it in your services. Let’s create a new project using this command:

spring init --dependencies=web --build=gradle --language=java spring-boot-internationalization

Then we can create a LocaleResolver class that will be responsible for defining user’s locale.

package com.jos.dem.springboot.internationalization.helper;

import java.util.List;
import java.util.Arrays;
import java.util.Locale;

import org.springframework.stereotype.Component;
import org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver;

import javax.servlet.http.HttpServletRequest;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class LocaleResolver extends AcceptHeaderLocaleResolver {

  private static final List<Locale> LOCALES = Arrays.asList(new Locale("en"), new Locale("es"));

  private Logger log = LoggerFactory.getLogger(this.getClass());

  public Locale resolveLocale(HttpServletRequest request) {
    String language = request.getHeader("Accept-Language");
    if (language == null || language.isEmpty()) {
      return Locale.getDefault();
    List<Locale.LanguageRange> list = Locale.LanguageRange.parse(language);
    Locale locale = Locale.lookup(list, LOCALES);
    return locale;


That’s it, here we have two locales supported: en and es. The locale should be passed in the header called “Accept-Language”. In Spring Boot we can read that header using HttpServletRequest, please consider the following controller:

package com.jos.dem.springboot.internationalization.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.beans.factory.annotation.Autowired;

import javax.servlet.http.HttpServletRequest;
import com.jos.dem.springboot.internationalization.services.LocaleService;

class InternationalizationController {

  private LocaleService localeService;

  public String index(HttpServletRequest request){
    return localeService.getMessage("user.hello", request);


As you can see we are creating an abstraction to use locale service and will be responsible for choosing right message according to specified locale.

package com.jos.dem.springboot.internationalization.services;

import javax.servlet.http.HttpServletRequest;

public interface LocaleService {
  String getMessage(String code, HttpServletRequest request);

Here is the implementation:

package com.jos.dem.springboot.internationalization.services.impl;

import org.springframework.stereotype.Service;
import org.springframework.context.MessageSource;
import org.springframework.beans.factory.annotation.Autowired;

import javax.servlet.http.HttpServletRequest;

import com.jos.dem.springboot.internationalization.helper.LocaleResolver;
import com.jos.dem.springboot.internationalization.services.LocaleService;

public class LocaleServiceImpl implements LocaleService {

  private MessageSource messageSource;
  private LocaleResolver localeResolver;

  public String getMessage(String code, HttpServletRequest request){
    return messageSource.getMessage(code, null, localeResolver.resolveLocale(request));


Under the resources folder we created two files: src/main/resources/i18n/messages.properties and src/main/resources/i18n/messages_es.properties. Here is the content of messages.properties:

user.hello=Hello from internationalization!

And here is content of messages_es.properties:

user.hello=¡Hola Internacionalización!

Now you can run the project:

gradle bootRun

In your browser go to this url: http://localhost:8080/ and you should see the message based in your browser language.

Here is our Junit Jupiter testing case, to cover LocaleResolver functionality:

package com.jos.dem.springboot.internationalization;

import static org.mockito.Mockito.when;
import static org.junit.jupiter.api.Assertions.assertEquals;

import java.util.Locale;
import javax.servlet.http.HttpServletRequest;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.DisplayName;

import org.mockito.Mock;
import org.mockito.InjectMocks;
import org.mockito.MockitoAnnotations;

import com.jos.dem.springboot.internationalization.helper.LocaleResolver;

class LocaleResolverTest {

  private LocaleResolver resolver = new LocaleResolver();

  private HttpServletRequest request;

  void setup() {

  @DisplayName("should get locale default")
  void shouldGetDefaultLocale() {
    Locale result = resolver.resolveLocale(request);
    assertEquals(Locale.getDefault(), result);

  @DisplayName("should get en-US as locale")
  void shodldGetEnLocale() {
    Locale result = resolver.resolveLocale(request);
    assertEquals(new Locale("en"), result);

  @DisplayName("should get es-MX as locale")
  void shouldGetEsLocale() {
    Locale result = resolver.resolveLocale(request);
    assertEquals(new Locale("es"), result);


To browse the code go here, to download the project:

git clone git@github.com:josdem/spring-boot-internationalization.git

To run the test:

gradle test

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