Locales as part of the URL in Spring MVC

Question

Hello!

I'm now looking for a framework for multilingual web-applications. At the moment it seems to me that the best choice is Spring MVC. But I faced the fact that all the guidelines for developers suggests to switch languages using LocaleChangeInterceptor in such way:

http://www.somesite.com/action/?locale=en

Unfortunately, there are a number of reasons why I would like avoid this. How could I make language code to be an essential part of URL? For example:

http://www.somesite.com/en/action

Thanks.

UPD: I've found following solution. It's not complete yet, but works. Solution consists in two parts - servlet filter and locale resolver bean. It's looks little bit hackish, but I do not see other way to solve this problem.

public class LocaleFilter implements Filter
{

    ...

    private static final String DEFAULT_LOCALE = "en";
    private static final String[] AVAILABLE_LOCALES = new String[] {"en", "ru"};

    public LocaleFilter() {} 

    private List<String> getSevletRequestParts(ServletRequest request)
    {
        String[] splitedParts = ((HttpServletRequest) request).getServletPath().split("/");
        List<String> result = new ArrayList<String>();

        for (String sp : splitedParts)
        {
            if (sp.trim().length() > 0)
                result.add(sp);
        }

        return result;
    }

    private Locale getLocaleFromRequestParts(List<String> parts)
    {
        if (parts.size() > 0)
        {
            for (String lang : AVAILABLE_LOCALES)
            {
                if (lang.equals(parts.get(0)))
                {
                    return new Locale(lang);
                }
            }
        }

        return null;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain) throws IOException, ServletException
    {
        List<String> requestParts = this.getSevletRequestParts(request);
        Locale locale = this.getLocaleFromRequestParts(requestParts);

        if (locale != null)
        {
            request.setAttribute(LocaleFilter.class.getName() + ".LOCALE", locale);

            StringBuilder sb = new StringBuilder();
            for (int i = 1; i < requestParts.size(); i++)
            {
                sb.append('/');
                sb.append((String) requestParts.get(i));
            }

            RequestDispatcher dispatcher = request.getRequestDispatcher(sb.toString());
            dispatcher.forward(request, response);
        }
        else
        {
            request.setAttribute(LocaleFilter.class.getName() + ".LOCALE", new Locale(DEFAULT_LOCALE));
            chain.doFilter(request, response);
        }
    }

    ...
}

public class FilterLocaleResolver implements LocaleResolver
{

    private Locale DEFAULT_LOCALE = new Locale("en");

    @Override
    public Locale resolveLocale(HttpServletRequest request)
    {
        Locale locale = (Locale) request.getAttribute(LocaleFilter.class.getName() + ".LOCALE");
        return (locale != null ? locale : DEFAULT_LOCALE);
    }

    @Override
    public void setLocale(HttpServletRequest request, HttpServletResponse response, Locale locale)
    {
        request.setAttribute(LocaleFilter.class.getName() + ".LOCALE", locale);
    }

}

So there is no need to map locale in each action in controllers. The following example will work fine:

@Controller
@RequestMapping("/test")
public class TestController
{

    @RequestMapping("action")
    public ModelAndView action(HttpServletRequest request, HttpServletResponse response)
    {
        ModelAndView mav = new ModelAndView("test/action");
        ...
        return mav;
    }

}

Answer 1

In spring 3.0 you can tell your controllers to look for path variables. e.g.

@RequestMapping("/{locale}/action")
public void action(@PathVariable String locale) {
    ...
}