How do I detect user preferred language when showing my website , website is java jsp based

Question

How do I detect user preferred language when showing my website , website is java jsp based. So I currently have

http://jthink.net/songkong/index.jsp

http://jthink.net/songkong/features.jsp

and was going to create a french version by recreating a french version in an fr subfolder

http://jthink.net/fr/songkong/index.jsp

http://jthink.net/fr/songkong/features.jsp

but do I ensure that if the user is using french as their computer language that they automaticaly get directed to the french version.

Answer 1

The trick is by working with "Accept-Language" sent by client (browser). Accept-Language is sent from the client in http header, and lets the server know the user's preferred language(s).

You will need to create a customer Filter (say MyFilter) and register it in web.xml.

public class MyFilter implements Filter {

    @Override
    public void init(FilterConfig config) throws ServletException {
        //
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws ServletException, IOException {
        HttpServletRequest request = (HttpServletRequest) req;          
        if(request.getParameter("language")==null) {
              String userLocale = request.getHeader("Accept-Language");
              Locale locale = request.getLocale();
              String requestURI = request.getRequestURI();

              // put your logic for userLocale and redirect accordingly          

             }
    }

    @Override
    public void destroy() {
        //
    }
}

Register in web.xml

<filter>
    <filter-name>localeFilter</filter-name>
    <filter-class>com.my.MyFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>localeFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

Update:

As suggested by @radimpe, the best practice will be using Persistent Cookie along with. This will help you, to trace, if some use wants to keep another language as default for your site

Answer 2

There are variety of ways in which you can do this :

I am assuming that user does not have to authenticate ?

Using Persistent Cookie for tracking the UPL - Disadvantages - when the user clears all the cookies manually - this preference is lost OR when the user is browsing in Private Mode then these cookies are not detected

IP Based - Assuming that there is no authentication for your website , you can do a predective Language detection by storing the IP and preference of the language. This again has the disadvantage - if the IP of the user changes

The combination of the two

The accept-language used alone , may be also a good criteria but then you would be binding the client to a specific language. It can be the starting point of determination