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Spring Webflux Internationalization

In this technical post, we will see how to use different languages in your Spring Webflux application along with Thymeleaf template framework. 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. Let’s create a new project using this command:

spring init --dependencies=webflux --build=gradle --language=java spring-webflux-internationalization

This is the build.gradle generated file:

buildscript {
  ext {
    springBootVersion = '2.1.2.RELEASE'
  }
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
  }
}

apply plugin: 'java'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'com.jos.dem.spring.webflux.internationalization'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
	mavenCentral()
}

dependencies {
  implementation('org.springframework.boot:spring-boot-starter-webflux')
  testImplementation('org.springframework.boot:spring-boot-starter-test')
  testImplementation('io.projectreactor:reactor-test')
}

Then add Thymeleaf dependency to your build.gradle file

implementation('org.thymeleaf:thymeleaf-spring5:3.0.11.RELEASE')

Spring Boot has an strategy interface for resolving messages, with support for internationalization of such messages.

@Bean
public MessageSource messageSource() {
  ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
  messageSource.setBasenames("i18n/messages");
  messageSource.setDefaultEncoding("UTF-8");
  return messageSource;
}

Now is time to configure template resolver, template engine and a view resolver since is what we need in order to configure Thymeleaf as html template.

@Bean
public ITemplateResolver thymeleafTemplateResolver() {
  final SpringResourceTemplateResolver resolver = new SpringResourceTemplateResolver();
  resolver.setApplicationContext(this.context);
  resolver.setPrefix("classpath:templates/");
  resolver.setSuffix(".html");
  resolver.setTemplateMode(TemplateMode.HTML);
  resolver.setCacheable(false);
  resolver.setCheckExistence(false);
  return resolver;
}

@Bean
public ISpringWebFluxTemplateEngine thymeleafTemplateEngine() {
  SpringWebFluxTemplateEngine templateEngine = new SpringWebFluxTemplateEngine();
  templateEngine.setTemplateResolver(thymeleafTemplateResolver());
  return templateEngine;
}

@Bean
public ThymeleafReactiveViewResolver thymeleafReactiveViewResolver() {
  ThymeleafReactiveViewResolver viewResolver = new ThymeleafReactiveViewResolver();
  viewResolver.setTemplateEngine(thymeleafTemplateEngine());
  return viewResolver;
}

@Override
public void configureViewResolvers(ViewResolverRegistry registry) {
  registry.viewResolver(thymeleafReactiveViewResolver());
}

Here is the complete complete web configuration

package com.jos.dem.spring.webflux.internationalization.config;

import org.springframework.context.MessageSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.reactive.config.EnableWebFlux;
import org.springframework.web.reactive.config.WebFluxConfigurer;
import org.springframework.context.support.ResourceBundleMessageSource;
import org.springframework.web.reactive.config.ViewResolverRegistry;

import org.thymeleaf.templatemode.TemplateMode;
import org.thymeleaf.templateresolver.ITemplateResolver;
import org.thymeleaf.spring5.SpringWebFluxTemplateEngine;
import org.thymeleaf.spring5.ISpringWebFluxTemplateEngine;
import org.thymeleaf.spring5.view.reactive.ThymeleafReactiveViewResolver;
import org.thymeleaf.spring5.templateresolver.SpringResourceTemplateResolver;

@Configuration
@EnableWebFlux
public class WebConfig implements ApplicationContextAware, WebFluxConfigurer {

  private ApplicationContext context;

  @Override
  public void setApplicationContext(ApplicationContext context) {
    this.context = context;
  }

  @Bean
  public MessageSource messageSource() {
    ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
    messageSource.setBasenames("i18n/messages");
    messageSource.setDefaultEncoding("UTF-8");
    return messageSource;
  }

  @Bean
  public ITemplateResolver thymeleafTemplateResolver() {
    final SpringResourceTemplateResolver resolver = new SpringResourceTemplateResolver();
    resolver.setApplicationContext(this.context);
    resolver.setPrefix("classpath:templates/");
    resolver.setSuffix(".html");
    resolver.setTemplateMode(TemplateMode.HTML);
    resolver.setCacheable(false);
    resolver.setCheckExistence(false);
    return resolver;
  }

  @Bean
  public ISpringWebFluxTemplateEngine thymeleafTemplateEngine() {
    SpringWebFluxTemplateEngine templateEngine = new SpringWebFluxTemplateEngine();
    templateEngine.setTemplateResolver(thymeleafTemplateResolver());
    return templateEngine;
  }

  @Bean
  public ThymeleafReactiveViewResolver thymeleafReactiveViewResolver() {
    ThymeleafReactiveViewResolver viewResolver = new ThymeleafReactiveViewResolver();
    viewResolver.setTemplateEngine(thymeleafTemplateEngine());
    return viewResolver;
  }

  @Override
  public void configureViewResolvers(ViewResolverRegistry registry) {
    registry.viewResolver(thymeleafReactiveViewResolver());
  }

}

As you can see SpringResourceTemplateResolver is in charge to set our template files path and extension. In this case will will define an index.html web page with a hello world message.

<html>
  <head>
    <meta charset="utf-8">
    <title>Internationalization with Spring Webflux</title>
  </head>
  <body>
  	<p th:text="#{user.hello}"></p>
  </body>
</html>

Also ResourceBundleMessageSource is defining message resources path for each supported language. In this case we will define messages.properties for English.

user.hello=Hello from internationalization!

And messages_es.properties for Spanish

user.hello=¡Hola Internacionalización!

Next step is to tell Spring to use a Locale resolver. So we need to add a configuration class which extends from DelegatingWebFluxConfiguration and returns our custom LocaleContextResolver.

package com.jos.dem.spring.webflux.internationalization.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.server.i18n.LocaleContextResolver;
import org.springframework.web.reactive.config.DelegatingWebFluxConfiguration;

import com.jos.dem.spring.webflux.internationalization.helper.LocaleResolver;

@Configuration
public class LocaleSupportConfig extends DelegatingWebFluxConfiguration {

  @Override
  protected LocaleContextResolver createLocaleContextResolver() {
    return new LocaleResolver();
  }

}

Here is our locale resolver

package com.jos.dem.spring.webflux.internationalization.helper;

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

import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.i18n.LocaleContextResolver;
import org.springframework.context.i18n.LocaleContext;
import org.springframework.context.i18n.SimpleLocaleContext;

public class LocaleResolver implements LocaleContextResolver {

  @Override
  public LocaleContext resolveLocaleContext(ServerWebExchange exchange) {
    String language = exchange.getRequest().getHeaders().getFirst("Accept-Language");

    Locale targetLocale = Locale.getDefault();
    if (language != null && !language.isEmpty()) {
      targetLocale = Locale.forLanguageTag(language);
    }
    return new SimpleLocaleContext(targetLocale);
  }

  @Override
  public void setLocaleContext(ServerWebExchange exchange, LocaleContext localeContext) {
    throw new UnsupportedOperationException("Not Supported");
  }

}

That’s it, we are reading language support in the headers from client request, in that way we can show the right message to our client whether is using English or Spanish. Finally here is our controller to render the index web page.

package com.jos.dem.spring.webflux.internationalization.handler;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class InternationalizationController {

  @GetMapping("/")
  public String index() {
    return "index";
  }

}

To run the project:

gradle bootRun

Then go to this address: http://localhost:8080. To browse the project go here, to download the project:

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

REST internationalization

If you need to use internationalization in a REST api instead of Thymeleaf, please consider this following changes.

package com.jos.dem.spring.webflux.internationalization.handler;

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

import com.jos.dem.spring.webflux.internationalization.service.LocaleService;

@RestController
public class InternationalizationController {

  @Autowired
  private LocaleService localeService;

  @GetMapping("/")
  public String index(ServerWebExchange exchange) {
    return localeService.getMessage("user.hello", exchange);
  }

}

Now we are using @RestController instead of @Controller and a locale service to resolve our messages.

package com.jos.dem.spring.webflux.internationalization.service;

import org.springframework.web.server.ServerWebExchange;

public interface LocaleService {
  String getMessage(String code, ServerWebExchange exchange);
}

Here is the implementation

package com.jos.dem.spring.webflux.internationalization.service.impl;

import org.springframework.stereotype.Service;
import org.springframework.context.MessageSource;
import org.springframework.context.i18n.LocaleContext;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.beans.factory.annotation.Autowired;

import com.jos.dem.spring.webflux.internationalization.service.LocaleService;
import com.jos.dem.spring.webflux.internationalization.helper.LocaleResolver;

@Service
public class LocaleServiceImpl implements LocaleService {

  @Autowired
  private MessageSource messageSource;
  @Autowired
  private LocaleResolver localeResolver;

  @Override
  public String getMessage(String code, ServerWebExchange exchange) {
    LocaleContext localeContext = localeResolver.resolveLocaleContext(exchange);
    return messageSource.getMessage(code, null, localeContext.getLocale());
  }

}

That’s it, we are using the same locale resolver as Thymeleaf but now is a @Component so we can use @Autowired to inject it

package com.jos.dem.spring.webflux.internationalization.helper;

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

import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.i18n.LocaleContextResolver;
import org.springframework.context.i18n.LocaleContext;
import org.springframework.context.i18n.SimpleLocaleContext;

@Component
public class LocaleResolver implements LocaleContextResolver {

  @Override
  public LocaleContext resolveLocaleContext(ServerWebExchange exchange) {
    String language = exchange.getRequest().getHeaders().getFirst("Accept-Language");

    Locale targetLocale = Locale.getDefault();
    if (language != null && !language.isEmpty()) {
      targetLocale = Locale.forLanguageTag(language);
    }
    return new SimpleLocaleContext(targetLocale);
  }

  @Override
  public void setLocaleContext(ServerWebExchange exchange, LocaleContext localeContext) {
    throw new UnsupportedOperationException("Not Supported");
  }

}

To run the project:

gradle bootRun

Then go to this address: http://localhost:8080. To browse the project go here, to download the project:

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

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