Create a Multi Language web application with Spring Boot

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1- The objective of the document

It is better to build a multilingual website because it helps your website to access to more users. The multilingual website is known as Internationalization (i18n) that is opposed to Localization (L10n).
The website (o7planning.org) that you are visiting is an internationalizing one. The website now supports in 2 languages including English , Vietnamese, French, German and Russian.
Note: Internationalization is a word comprising 18 characters, the first character is i and the last one is n, so it is commonly abbreviated as i18n.
Spring provides extensive support for internationalization (i18n) through the use of Spring interceptors, Locale Resolvers and Resource Bundles for different locales.
In this post, I will guide you to build  a simple multilingual website using Spring Boot.

You can preview the example below:

In the example, the locale information lies on the parameter of the URL. Locale information will stored in Cookie, and the user does not reselect language in the next pages.
  • http://localhost:8080/SomeContextPath/login1?lang=vi
  • http://localhost:8080/SomeContextPath/login1?lang=fr
Another example of the Locale information on URL:
  • http://localhost:8080/SomeContextPath/vi/login2
  • http://localhost:8080/SomeContextPath/en/login2

2- Create Spring Boot project

3- Message Resources

I here create 3 properties files for the languages including: English, French and Vietnamese. These files will loaded and managed by messageResource Bean.
i18n/messages_en.properties
#Generated by Eclipse Messages Editor (Eclipse Babel)

label.password = Password
label.submit   = Login
label.title    = Login Page
label.userName = User Name

 
i18n/messages_fr.properties
#Generated by Eclipse Messages Editor (Eclipse Babel)

label.password = Mot de passe
label.submit   = Connexion
label.title    = Connectez-vous page
label.userName = Nom d'utilisateur

 
i18n/messages_vi.properties
#Generated by Eclipse Messages Editor (Eclipse Babel)

label.password = M\u1EADt kh\u1EA9u
label.submit   = \u0110\u0103ng nh\u1EADp
label.title    = Trang \u0111\u0103ng nh\u1EADp
label.userName = T\u00EAn ng\u01B0\u1EDDi d\u00F9ng
 
Eclipse supports you in edit the file's information by using "Message Editor".

4- Interceptor & LocaleResolver

You need to declare 2 Spring BEANs including localeResolver and messageResource.

localeResolver - Specifies how to get Locale information that the user will use. CookieLocaleResolver will read the Locale information from Cookie in order to find that which languges the user used before.

messageResource - Will load the content of the properties files 
Before request is processed by Controller, it has to pass through Interceptors where you need to register LocaleChangeInterceptor, the Interceptor processes the Locale changes from the user.
WebMvcConfig.java
package org.o7planning.sbi18n.config;

 
import org.springframework.context.MessageSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.ReloadableResourceBundleMessageSource;
import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.i18n.CookieLocaleResolver;
import org.springframework.web.servlet.i18n.LocaleChangeInterceptor;

@Configuration 
public class WebMvcConfig implements WebMvcConfigurer {

	 
	@Bean(name = "localeResolver")
	public LocaleResolver getLocaleResolver()  {
		CookieLocaleResolver resolver= new CookieLocaleResolver();
		resolver.setCookieDomain("myAppLocaleCookie");
		// 60 minutes 
		resolver.setCookieMaxAge(60*60); 
		return resolver;
	} 
	
	@Bean(name = "messageSource")
	public MessageSource getMessageResource()  {
		ReloadableResourceBundleMessageSource messageResource= new ReloadableResourceBundleMessageSource();
		
		// Read i18n/messages_xxx.properties file.
		// For example: i18n/messages_en.properties
		messageResource.setBasename("classpath:i18n/messages");
		messageResource.setDefaultEncoding("UTF-8");
		return messageResource;
	}
	@Override
	public void addInterceptors(InterceptorRegistry registry) {
		LocaleChangeInterceptor localeInterceptor = new LocaleChangeInterceptor();
		localeInterceptor.setParamName("lang");
		
		
		registry.addInterceptor(localeInterceptor).addPathPatterns("/*");
	}
	
}

5- Controller & Views

MainController.java (Locale on Parameter)
package org.o7planning.sbi18n.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class MainController {

    @RequestMapping(value = { "/", "/login1" })
    public String staticResource(Model model) {
        return "login1";
    }

}
login1.html (Thymeleaf View)
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8">
      <title th:utext="#{label.title}"></title>
   </head>
   <body>
      <div style="text-align: right;padding:5px;margin:5px 0px;background:#ccc;">
         <a th:href="@{/login1?lang=en}">Login (English)</a>
         &nbsp;|&nbsp;
         <a th:href="@{/login1?lang=fr}">Login (French)</a>
         &nbsp;|&nbsp;
         <a th:href="@{/login1?lang=vi}">Login (Vietnamese)</a>
      </div>
      <form method="post" action="">
         <table>
            <tr>
               <td>
                  <strong th:utext="#{label.userName}"></strong>
               </td>
               <td><input name="userName" /></td>
            </tr>
            <tr>
               <td>
                  <strong  th:utext="#{label.password}"></strong>
               </td>
               <td><input name="password" /></td>
            </tr>
            <tr>
               <td colspan="2">
                  <input type="submit" th:value="#{label.submit}" />
               </td>
            </tr>
         </table>
      </form>
   </body>
</html>
Case, you use JSP technology for the View layer.
See more:
src/main/webapp/WEB-INF/jsp/login1.jsp (JSP View)
<%@taglib uri="http://www.springframework.org/tags" prefix="spring"%>
<%@ page contentType="text/html; charset=UTF-8" %>
<%@ page session="false"%>

<!DOCTYPE html>

<html>
<head>

<meta charset="UTF-8">

<title><spring:message code="label.title" /></title>
</head>
<body>

    <div style="text-align: right;padding:5px;margin:5px 0px;background:#ccc;">
       <a href="${pageContext.request.contextPath}/login1?lang=en">Login (English)</a>
       &nbsp;|&nbsp;
       <a href="${pageContext.request.contextPath}/login1?lang=fr">Login (French)</a>
       &nbsp;|&nbsp;
       <a href="${pageContext.request.contextPath}/login1?lang=vi">Login (Vietnamese)</a>
    </div>

    <form method="post" action="">
        <table>
            <tr>
                <td>
                 <strong>
                <spring:message    code="label.userName" />
                </strong>
                </td>
                <td><input name="userName" /></td>
            </tr>
            <tr>
                <td>
                 <strong>
                <spring:message    code="label.password" />
                </strong>
                </td>
                <td><input name="password" /></td>
            </tr>
            <tr>
                <td colspan="2">
                <spring:message code="label.submit" var="labelSubmit"></spring:message>
                <input type="submit" value="${labelSubmit}" />
                </td>
            </tr>
        </table>
    </form>
</body>
</html>

6- Locale information on the URL

In the case that you want to build a multilingual website which the Locale information lies on URL. You need to change some configures:
  • http://localhost:8080/SomeContextPath/vi/login2
  • http://localhost:8080/SomeContextPath/en/login2
Create 2 classes - UrlLocaleInterceptor and UrlLocaleResolver.
UrlLocaleInterceptor.java
package org.o7planning.sbi18n.interceptor;

import java.util.Locale;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
import org.springframework.web.servlet.support.RequestContextUtils;

public class UrlLocaleInterceptor extends HandlerInterceptorAdapter {

   @Override
   public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
           throws Exception {

       LocaleResolver localeResolver = RequestContextUtils.getLocaleResolver(request);

       if (localeResolver == null) {
           throw new IllegalStateException("No LocaleResolver found: not in a DispatcherServlet request?");
       }

       // Get Locale from LocaleResolver
       Locale locale = localeResolver.resolveLocale(request);

       localeResolver.setLocale(request, response, locale);

       return true;
   }

}
UrlLocaleResolver.java
package org.o7planning.sbi18n.resolver;

import java.util.Locale;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.LocaleResolver;

public class UrlLocaleResolver implements LocaleResolver {

    private static final String URL_LOCALE_ATTRIBUTE_NAME = "URL_LOCALE_ATTRIBUTE_NAME";

    @Override
    public Locale resolveLocale(HttpServletRequest request) {
        // ==> /SomeContextPath/en/...
        // ==> /SomeContextPath/fr/...
        // ==> /SomeContextPath/WEB-INF/pages/...
        String uri = request.getRequestURI();

        System.out.println("URI=" + uri);

        String prefixEn = request.getServletContext().getContextPath() + "/en/";
        String prefixFr = request.getServletContext().getContextPath() + "/fr/";
        String prefixVi = request.getServletContext().getContextPath() + "/vi/";

        Locale locale = null;

        // English
        if (uri.startsWith(prefixEn)) {
            locale = Locale.ENGLISH;
        }
        // French
        else if (uri.startsWith(prefixFr)) {
            locale = Locale.FRANCE;
        }
        // Vietnamese
        else if (uri.startsWith(prefixVi)) {
            locale = new Locale("vi", "VN");
        }
        if (locale != null) {
            request.getSession().setAttribute(URL_LOCALE_ATTRIBUTE_NAME, locale);
        }
        if (locale == null) {
            locale = (Locale) request.getSession().getAttribute(URL_LOCALE_ATTRIBUTE_NAME);
            if (locale == null) {
                locale = Locale.ENGLISH;
            }
        }
        return locale;
    }

    @Override
    public void setLocale(HttpServletRequest request, HttpServletResponse response, Locale locale) {
        // Nothing
    }

}
Re-change the Interceptor configuration in WebMvcConfig:
WebMvcConfig.java
package org.o7planning.sbi18n.config;

import org.o7planning.sbi18n.interceptor.UrlLocaleInterceptor;
import org.o7planning.sbi18n.resolver.UrlLocaleResolver;
import org.springframework.context.MessageSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.ReloadableResourceBundleMessageSource;
import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

	@Bean(name = "messageSource")
	public MessageSource getMessageResource() {
		ReloadableResourceBundleMessageSource messageResource = new ReloadableResourceBundleMessageSource();

		// Read i18n/messages_xxx.properties file.
		// For example: i18n/messages_en.properties
		messageResource.setBasename("classpath:i18n/messages");
		messageResource.setDefaultEncoding("UTF-8");
		return messageResource;
	}

	// To solver URL like:
	// /SomeContextPath/en/login2
	// /SomeContextPath/vi/login2
	// /SomeContextPath/fr/login2
	@Bean(name = "localeResolver")
	public LocaleResolver getLocaleResolver() {
		LocaleResolver resolver = new UrlLocaleResolver();
		return resolver;
	}

	@Override
	public void addInterceptors(InterceptorRegistry registry) {

		UrlLocaleInterceptor localeInterceptor = new UrlLocaleInterceptor();

		registry.addInterceptor(localeInterceptor).addPathPatterns("/en/*", "/fr/*", "/vi/*");
	}

}
Controller:
MainController2.java (Locale on URL)
package org.o7planning.sbi18n.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class MainController2 {

    @RequestMapping(value = "/{locale:en|fr|vi}/login2")
    public String login2(Model model) {
        return "login2";
    }

}
index2.html (Thymeleaf View)
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8">
      <title th:utext="#{label.title}"></title>
   </head>
   <body>
      <div style="text-align: right;padding:5px;margin:5px 0px;background:#ccc;">
         <a th:href="@{/en/login2}">Login (English)</a>
         &nbsp;|&nbsp;
         <a th:href="@{/fr/login2}">Login (French)</a>
         &nbsp;|&nbsp;
         <a th:href="@{/vi/login2}">Login (Vietnamese)</a>
      </div>
      <form method="post" action="">
         <table>
            <tr>
               <td>
                  <strong th:utext="#{label.userName}"></strong>
               </td>
               <td><input name="userName" /></td>
            </tr>
            <tr>
               <td>
                  <strong  th:utext="#{label.password}"></strong>
               </td>
               <td><input name="password" /></td>
            </tr>
            <tr>
               <td colspan="2">
                  <input type="submit" th:value="#{label.submit}" />
               </td>
            </tr>
         </table>
      </form>
   </body>
</html>
login2.jsp (JSP View)
<%@taglib uri="http://www.springframework.org/tags" prefix="spring"%>
<%@ page contentType="text/html; charset=UTF-8" %>
<%@ page session="false"%>

<!DOCTYPE html>

<html>
<head>

<meta charset="UTF-8">

<title><spring:message code="label.title" /></title>
</head>
<body>

    <div style="text-align: right;padding:5px;margin:5px 0px;background:#ccc;">
       <a href="${pageContext.request.contextPath}/en/login2">Login (English)</a>
       &nbsp;|&nbsp;
       <a href="${pageContext.request.contextPath}/fr/login2">Login (French)</a>
       &nbsp;|&nbsp;
       <a href="${pageContext.request.contextPath}/vi/login2">Login (Vietnamese)</a>
    </div>
 
    <form method="post" action="">
        <table>
            <tr>
                <td>
                 <strong>
                <spring:message    code="label.userName" />
                </strong>
                </td>
                <td><input name="userName" /></td>
            </tr>
            <tr>
                <td>
                 <strong>
                <spring:message    code="label.password" />
                </strong>
                </td>
                <td><input name="password" /></td>
            </tr>
            <tr>
                <td colspan="2">
                <spring:message code="label.submit" var="labelSubmit"></spring:message>
                <input type="submit" value="${labelSubmit}" />
                </td>
            </tr>
        </table>
    </form>
</body>
</html>
Running the apps:

7- Multilingual websites with content stored in DB

The example of a multilingual website above is unable to satisfy you. You have the demand for a news website with multiple languages, and its content is stored in Database. A solution you can use multiple Datasources in which each datasoure is a database containing the content of a language.
You can see more at:
  • TODO Link?
  • TODO

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