MessageSource (Spring Boot)

<dependency>

    <groupId>org.springframework.boot</groupId>

    <artifactId>spring-boot-starter-web</artifactId>

</dependency>

<dependency>

    <groupId>org.springframework.boot</groupId>

    <artifactId>spring-boot-starter-validation</artifactId>

</dependency>

package edu.cou.app;

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.validation.beanvalidation.LocalValidatorFactoryBean;

/**

 * I18n configuration (MessageSource).<br>

 * <br>

 * An application context delegates the message resolution to a bean with the exact name

 * messageSource.

 */

@Configuration

public class MessageSourceConfig {

  /**

   * ReloadableResourceBundleMessageSource is the most common MessageSource implementation that

   * resolves messages from resource bundles for different locales.

   * 

   * @return The MessageSource instance

   */

  @Bean

  public MessageSource messageSource() {

    val messageSource = new ReloadableResourceBundleMessageSource();

    messageSource.setAlwaysUseMessageFormat(true);

    messageSource.setBasename("classpath:messages");

    messageSource.setDefaultEncoding("UTF-8");

    return messageSource;

  }

  /**

   * To use custom name messages in a properties file like we need to define a

   * LocalValidatorFactoryBean and register the messageSource.<br>

   * <br>

   * Example:<br>

   * 

   * <pre>

   * &#64;NotEmpty(message = "{email.notempty}")<br>

   * &#64;Email<br>

   * private String email;<br>

   * </pre>

   * 

   * @return The LocalValidatorFactoryBean instance

   */

  @Bean

  public LocalValidatorFactoryBean getValidator() {

    LocalValidatorFactoryBean bean = new LocalValidatorFactoryBean();

    bean.setValidationMessageSource(messageSource());

    return bean;

  }

}

package edu.cou.app.service;

import java.util.Locale;

import javax.inject.Inject;

import org.springframework.context.MessageSource;

import org.springframework.context.NoSuchMessageException;

import org.springframework.lang.Nullable;

import org.springframework.stereotype.Service;

import edu.cou.app.exception.AppException;

import lombok.extern.slf4j.Slf4j;

/**

 * i18n service.

 */

@Slf4j

@Service

public final class I18nService {

  /** i18n literals */

  private MessageSource messageSource;

  /**

   * Constructor.

   * 

   * @param messageSource I18n message source

   */

  @Inject

  public I18nService(final MessageSource messageSource) {

    this.messageSource = messageSource;

  }

  /**

   * $(key, langIso639p1Code, arguments).<br>

   * <br>

   * Sample pattern: "S''ha detectat que la petició {0} és repetida"<br>

   * where {0} will be replaced by the actual argument.<br>

   * <br>

   * 

   * @param key              Eg: "argument_blank"

   * @param langIso639p1Code Eg: "en"

   * @param args             Nullable. N arguments for replacing pattern place holders {0}, {1},

   *                         etc.

   * @return parameterized translated text

   * @throws AppException -

   */

  @SuppressWarnings({ "checkstyle:methodname" })

  public String $( // NOSONAR

      final String key, final String langIso639p1Code, @Nullable final Object... args) {

    //

    String ret;

    try {

      ret = this.messageSource.getMessage(key, args, this.getLocale(langIso639p1Code));

    } catch (NoSuchMessageException t) {

      log.warn(String.format("No message exists for key=%s, lang=%s", key, langIso639p1Code), t);

      ret = key;

    }

    return ret;

  }

  /**

   * $(key, langIso639p1Code).<br>

   * <br>

   * <b>Eclipse config</b> | Preferences > Java > Compiler > Error/Warnings > Unhandled token in

   * '@SuppresWarnings': Ignore<br>

   * <br>

   * 

   * @param key              Eg: "http_504"

   * @param langIso639p1Code Eg: "cmn"

   * @return Message in lang 'langIanaCode' or, if not found, the key

   */

  @SuppressWarnings({ "checkstyle:methodname" })

  public String $(final String key, final String langIso639p1Code) { // NOSONAR

    return this.$(key, langIso639p1Code, (Object[]) null);

  }

  /**

   * $(key).<br>

   * 

   * @param key Eg: "argument_blank" translated in default language

   * @return fixed translated text

   */

  @SuppressWarnings({ "checkstyle:methodname" })

  public String $(final String key) { // NOSONAR

    return this.$(key, LangService.DEFAULT_ISO639P1_CODE, (Object[]) null);

  }

  /**

   * 

   * @param langIso639p1Code

   * @return Locale for 'langIso639p1Code'

   */

  private Locale getLocale(final String langIso639p1Code) {

    Locale ret;

    if (LangService.ENGLISH_ISO639P1_CODE.equals(langIso639p1Code)) {

      ret = Locale.ENGLISH;

    } else if (LangService.CASTILIAN_ISO639P1_CODE.equals(langIso639p1Code)) {

      ret = new Locale("es", "ES");

    } else if (LangService.CATALAN_ISO639P1_CODE.equals(langIso639p1Code)) {

      ret = new Locale("ca", "ES");

    } else {

      log.warn("App does not have message source for langIso639p1Code=" + langIso639p1Code);

      ret = this.getLocale(LangService.DEFAULT_ISO639P1_CODE);

    }

    return ret;

  }

}

# messages.properties

email.nonempty=Please provide a valid email address

# messages_pl.properties

email.nonempty=Prosimy o wprowadzenie poprawnego adresu e-mailowego

public class Example {

  @NotEmpty(message = "{email.nonempty}")

  @Email

  private email;

}

package edu.cou.app;

import javax.inject.Inject;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

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.LocaleChangeInterceptor;

import org.springframework.web.servlet.i18n.SessionLocaleResolver;

/**

 * Determine which locale is currently being used.<br>

 * It allows, eg, that the validation constrain annotations pick up the proper MessageSource

 * language.<br>

 * 

 */

@Configuration

public class LocaleConfig implements WebMvcConfigurer {

  private I18nService i18nService;

  /**

   * In order for our application to be able to determine which locale is currently being used.

   * 

   * @return -

   */

  @Bean

  public LocaleResolver localeResolver() {

    SessionLocaleResolver slr = new SessionLocaleResolver();

    slr.setDefaultLocale(Locale.ENGLISH);

    return slr;

  }

  /**

   * Add an interceptor bean that will switch to a new locale based on the value of the "lang" query

   * string parameter appended to a request.<br>

   * Eg: /entities/27?lang=pl<br>

   * <br>

   * Note: In order to take effect, this bean needs to be added to the application's interceptor

   * registry

   * 

   * @return -

   */

  @Bean

  public LocaleChangeInterceptor localeChangeInterceptor() {

    LocaleChangeInterceptor lci = new LocaleChangeInterceptor();

    lci.setParamName("lang");

    return lci;

  }

  /**

   * Register the LocaleChangeInterceptor

   */

  @Override

  public void addInterceptors(InterceptorRegistry registry) {

    registry.addInterceptor(localeChangeInterceptor());

  }

}