How to reuse Spring or Java's locale lookup code?

I am doing a Spring web application.

I need to support a few locales such as ko (Korean), ru (Russian), en (English), etc.

I am able to catch what locale is from a browser via ways such as RequestContextUtils.getLocale(request) or LocaleChangeInterceptor.

However, the browser's locale may not be what my web app supports. I have to resolve it to the closet or default locale.

Basically, I need to know how to get the resolved locale given the browser's locale AND a few locale values such as ko, ru, and en.

My understanding is that Spring has such locale resolution code because it is able to find right resource bundles given a browser's locale. I am hoping to reuse Spring's code for locale resolution, but not sure how to do it. Please note that this question has nothing to do with finding the brwoser's locale or displaying proper messages.

EDIT

Based on my tracing Spring's code, it appears that Spring depends on JDK to find the exact or closest locale. I just found out this and think this is what I am looking for:

Resource Bundle Lookup Order https://sites.google.com/site/openjdklocale/design-notes/resource-bundle-lookup-order

Please note that I don't need to find right resource bundle. I just need to get the locale the existing JDK code returns given a locale in question and a few known locales. So I am hoping to reuse existing JDK's lookup code. Any idea?

I am using JDK 7.

Thanks for any help and input!

Regards.

Solution

Complete Reuse

To reuse the JDK logic, you could create a property file within the classpath for each of the known locales (such as test_fr_CA.properties, test_fr.properties, test_en_US.properties, test_en.properties, test.properties). Don't forget the root locale (test.properties) if you want to be able to match to it. Then simply create a resource bundle for the locale in question and inspect it to see the actual locale used.

ResourceBundle rb = ResourceBundle.getBundle("test", Locale.FRENCH);
System.out.println("Locale used is:"+rb.getLocale().toString());

The files can be created dynamically and cleaned up after the test.

High Level Code Replication, Low Level Reuse

You could replicate the high level code in java.util.ResourceBundle.getBundleImpl(...). This is basically going through looking for a match (using your own matching logic like equal toString() representations) in a candidate list of locales reusing java.util.ResourceBundle.Control.getCandidateLocales(...) on the locale in question. If there is no match you get the next fallback locale for the locale in question by reusing java.util.ResourceBundle.Control.getFallbackLocale(...) For each fallback locale you try to match a locale in it's candidate list repeating the fallback in a loop until there are no fallback locales left. Note that the root locale will be the last candidate in each candidate list but it should be skipped unless you have exhausted all fallback locales.

This method does not require creating files. You use a non-existent baseName in the getCandidateLocales(...) and get FallbackLocale(...) calls and compare each candidate locale to your list of known locales looking for a match.

A simple example of this would be like the following:

    ResourceBundle.Control rbControl = ResourceBundle.Control.getControl(ResourceBundle.Control.FORMAT_PROPERTIES);
    Locale localeInQuestion = Locale.CHINA;
    List<Locale> knownLocales = Arrays.asList(new Locale[] {Locale.CANADA_FRENCH, Locale.FRENCH, Locale.US, Locale.UK, Locale.ENGLISH, Locale.ROOT});
    String nonExistentBaseName = "bogus";

    Locale matchingLocale = null;
    Boolean reachedRootLocaleMatch = false;

    outerloop:
    for (Locale targetLocale = localeInQuestion;
            targetLocale != null;
            targetLocale = rbControl.getFallbackLocale(nonExistentBaseName, targetLocale)) {
        List<Locale> candidateLocales = rbControl.getCandidateLocales(nonExistentBaseName, targetLocale);
        for (Iterator iterator = candidateLocales.iterator(); iterator.hasNext();) {
            Locale currentCandidateLocale = (Locale) iterator.next();
            if (knownLocales.contains(currentCandidateLocale)) {
                if (currentCandidateLocale.equals(Locale.ROOT)) {
                    reachedRootLocaleMatch = true;
                }
                else {
                    matchingLocale = currentCandidateLocale;
                    break outerloop;
                }
            }
        }
    }

    if (matchingLocale == null && reachedRootLocaleMatch) {
        matchingLocale = Locale.ROOT;
    }

    if (matchingLocale != null) {
        System.out.println("The matching locale is: "+matchingLocale.toString());
    }
    else {
        System.out.println("There was no matching locale");
    }