I had to implement locale awareness in a Spring Boot application. The client would send its preferred languages in the Accept-Language header and the application should respect that.

You can inject a Locale in your Spring MVC controller, which then should contain the locale the client has chosen.

To get Spring Boot to inject the locale from the Accept-Language header in the Locale controller parameter, install the following bean:

// Do not rename that bean, otherwise Spring MVC won't pick it up!
@Bean("localeResolver") 
public LocaleResolver acceptHeaderLocaleResolver() {
    AcceptHeaderLocaleResolver resolver = new AcceptHeaderLocaleResolver();

    resolver.setDefaultLocale(Locale.GERMAN);
    resolver.setSupportedLocales(Arrays.asList(
            Locale.GERMAN,
            Locale.US,
            Locale.FRENCH
    ));

    return resolver;
}

setDefaultLocale sets the default locale, if the client doesn’t provide one. setSupportedLocales sets the supported locales. If the client sends one which isn’t supported, the default locale is used.

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