Tuesday, December 1, 2009

Selecting the locale for an user with JSTL

In another post, I introduced the basic internationalization capabilities built in JSTL. The algorithm used to choose a suitable locale for an user is a good default choice: without any effort, your web application will show up in the correct locale.

But what if you wanted to let the user choose the locale?

Well, the JSTL Specification lets you establish a locale and a scope: such as page, request, session, application. The first sketch I'd come up with would be something like creating a servlet to enforce the programmatic configuration.

Language selector servlet

This is a servlet service method prototype:

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    final String lang = request.getParameter("lang");
    if (isSupported(lang)) {
        Config.set(request.getSession(), Config.FMT_LOCALE, lang);

    request.getRequestDispatcher("/").forward(request, response);

The important call here is Config.set(...): you're telling JSTL to use the specified locale (as a String) and save it in the session scope. This servlet accepts the lang parameter and, if present, uses it to determine if it represents a supported locale (isSupported implementation is omitted). If it is, it uses it as described above. At the end of it all, forwards the user at the web welcome page (if any).


The servlet described above is the first step towards a complete user customization and is just an example of how you can use the JSTL's Config class. Desirable improvements might be:
  • Saving the user servlet in its profile (if the user has been authenticated) so that future sessions will automatically use the user-specified locale.
  • Using a servlet filter instead of a servlet to automatically intercept the lang parameter and leave the web navigation unaffected.

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