Fallback locale other than the system locale in AbstractResourceBasedMessageSource

[sonOfRa]

It's already possible to fallback to the System Locale in, for example ResourceBundleMessageSource. In my current case, I don't want to fall back to the system locale, but I want to fallback to the same Default Locale that the rest of our system uses.

import org.springframework.context.MessageSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.MessageSourceAccessor;
import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.i18n.SessionLocaleResolver;

import java.util.Locale;

@Configuration
public class ResourceConfig implements WebMvcConfigurer {

    private static final Locale DEFAULT_LOCALE = Locale.GERMAN;

    @Bean
    public LocaleResolver localeResolver() {
        SessionLocaleResolver slr = new SessionLocaleResolver();
        slr.setDefaultLocale(DEFAULT_LOCALE);
        return slr;
    }

    @Bean
    public MessageSourceAccessor messageSourceAccessor(MessageSource messageSource) {
        return new MessageSourceAccessor(messageSource, DEFAULT_LOCALE);
    }
}

I already attempted this through the MessageSourceAccessor Bean above, but that only seems to configure the default locale when invoking getMessage(...) without specifying an explicit locale manually.

So the behaviour I would expect is, that if I have message files messages_{en,de}.properties, and then a call like messageSourceAccessor.getMessage("message.key", Locale.FRENCH) would return the german string configured for message.key in messages_de.properties

[sonOfRa]

There's a workaround presented in this stackoverflow question: https://stackoverflow.com/questions/49561374/spring-messagesource-fallback-to-explicit-locale.

It kind of works, but I would expect the possibility of a static fallback locale to be working out of the box, instead of requiring a hacky workaround that has to use Exceptions for control flow.

[philwebb]

It looks like we'd need some changes in Spring Framework to support this in Spring Boot. I've transferred the issue for that team to consider.

[rstoyanchev]

So we need setDefaultLocale(Locale) in AbstractResourceBasedMessageSource as an alternative to the setFallbackToSystemLocale. Does that seem right @jhoeller?

[rstoyanchev]

Tentatively scheduled for 5.2.2 as it seems straight forward enough.

[jhoeller]

Indeed, I've introduced a setDefaultLocale(Locale) method along those lines, and a ´getDefaultLocale()` delegate which resolves either such a locally specified Locale or (dynamically) the system Locale, preserving the previous behavior.