RequestURI Locale Interceptor for Spring

Handling Locale as first part of RequestURI.

Example:

HTTP Request	RequestURI
https://foo.bar/{locale}/some/path.html	/{locale}/some/path.html
https://foo.bar/{locale}/a.html	/{locale}/a.html
https://foo.bar/{locale}/xyz?a=b	/{locale}/xyz

Locale Resolution

The first path segment of the RequestURI determines the java.util.Locale that Spring uses for the request (e.g. LocaleContextHolder.getLocale(), MessageSource, RequestContextUtils.getLocale(request)).

• If the first segment is one of the supportedLocales, that locale from the URL becomes the Locale of the request.
• If it is missing or not supported, the request is redirected to the same path prefixed with the defaultLocale (or to defaultRequestURI if no path remains). The Locale of the request is then the defaultLocale.

RequestURI	Redirect to	Locale
/en/some/path.html	-	en
/en-us/some/path.html	-	en-US
/de/some/path.html	-	de
/fr/some/path.html	/en/some/path.html	en (defaultLocale)
/some/path.html	/en/path.html	en (defaultLocale)
/	/en (or defaultRequestURI)	en (defaultLocale)

The examples assume supportedLocales are en, en-US and de, and defaultLocale is en.

Dependency

Maven

<dependency>
    <groupId>io.github.alaugks</groupId>
    <artifactId>spring-requesturi-locale-interceptor</artifactId>
    <version>1.0.0</version>
</dependency>

Gradle

implementation group: 'io.github.alaugks', name: 'spring-requesturi-locale-interceptor', version: '1.0.0'

Configuration

builder(Locale defaultLocale) (required)

• Argument Locale defaultLocale: Defines the default and fallback locale.

supportedLocales(List<Locale> locales)

• Lists all locales that are supported.

defaultRequestURI(String path)

• Defines the path to redirect to if the RequestURI is empty. If not set, the default RequestURI is /{defaultLocale}.

Spring Configuration

import io.github.alaugks.spring.requesturilocaleinterceptor.RequestURILocaleInterceptor;
import io.github.alaugks.spring.requesturilocaleinterceptor.RequestURILocaleResolver;
import java.util.List;
import java.util.Locale;
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;

@Configuration
public class WebMvcConfigurerConfig implements WebMvcConfigurer {

    private final Locale defaultLocale = Locale.forLanguageTag("en");

    private final List<Locale> supportedLocales = List.of(
        Locale.forLanguageTag("en"),
        Locale.forLanguageTag("de"),
        Locale.forLanguageTag("en-US")
    );

    @Bean
    public LocaleResolver localeResolver() {
        RequestURILocaleResolver resolver = new RequestURILocaleResolver();
        resolver.setDefaultLocale(this.defaultLocale);
        return resolver;
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        RequestURILocaleInterceptor interceptor = RequestURILocaleInterceptor
            .builder(this.defaultLocale)
            .supportedLocales(this.supportedLocales)
            .defaultRequestURI("/en/home")
            .build();
        
        registry.addInterceptor(urlInterceptor)
            .addPathPatterns("/**")
            // Exclude from Interceptor
            .excludePathPatterns("/static/**", "/error");
    }
}

Example

A complete, runnable Spring Boot application is available in the spring-messagesource-xliff-example repository. It shows this interceptor in action, resolving the locale from the first path segment of the request URI (e.g. /en/..., /de/...).