public  void destroy() 
{
    //~ Methods ----------------------------------------------------------------
        _config           = null;
        _context          = null;
        _welcomeFiles     = null;
}

 public  void doFilter(ServletRequest request,
    ServletResponse response,
    FilterChain chain) throws IOException, ServletException 
{
        if (_config == null)
        {
            return;
        }
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        String             uri = httpRequest.getRequestURI();
        // if the uri does not contain a suffix, we consider 
        // it to represent a directory / context, not a file.
        // file has suffix.  No need to search for welcome file
        if (uri.lastIndexOf('.")  > uri.lastIndexOf('/"))
        {
            chain.doFilter(request, response);
            return;
        }
        String       contextPath = httpRequest.getContextPath();
        String       welcomeFile = null;
        StringBuffer sb          = new StringBuffer(uri);
        if (!uri.endsWith("/"))
        {
            sb.append('/");
        }
        String baseURI = sb.delete(
                0,
                contextPath.length()).toString();
        // REVISIT: we probably can check for existence once at startup 
        //          and know the exact welcome file by now. Of course, that 
        //          would not work if the files change at runtime, but does it matter?
        for (int i = 0; i <  _welcomeFiles.length; i++)
        {
            sb.setLength(0);
            sb.append(baseURI).append(_welcomeFiles[i]);
            File file = new File(_context.getRealPath(sb.toString()));
            //            			context.log("Welcome File: " + file.getAbsolutePath());
            if (file.exists())
            {
                // REVISIT: This will force all "welcome" JSPs through MyFaces. 
                //           Shouldn't we allow the user to enter *.jsf and check for *.jsp for existence, instead? 
                if (_welcomeFiles[i].endsWith(".jsp"))
                {
                    // alter the name of the file we are requesting to
                    // force it through the MyFacesServlet
                    sb.replace(
                        sb.lastIndexOf(".jsp"),
                        sb.length(),
                        ".jsf");
                    welcomeFile = sb.toString();
                }
                // we have discovered a filename;
                // stop the loop
                break;
            }
        }
        if (welcomeFile == null)
        {
            sb.setLength(0);
            sb.append(baseURI);
            sb.append("index.jsf");
            welcomeFile = sb.toString();
        }
        RequestDispatcher rd = httpRequest.getRequestDispatcher(welcomeFile);
        rd.forward(request, response);
        return;
}

If the URI indicates a context, or a subdirectory within a particular context, but does not specify a filename, the request is redirected to one of the default welcome files, assuming they are provided in the web.xml file. If no welcome files are specified, or if none of the welcome files actually exists, then the request is redirected to a file named "index.jsp" for that context or subdirectory with the current context. If the index.jsp file does not exist, the servlet will return a File Not Found Error 404 message. A well configured servlet should provide a means of handling this type of error, along with a link to an appropriate help page. A URI is thought to represent a context and/or subdirectory(s) if it lacks a suffix following the pattern .suffix.

 public  void init(FilterConfig config) throws ServletException 
{
        if (config == null)
        {
            return;
        }
        this._config      = config;
        this._context     = config.getServletContext();
        try
        {
            SAXParserFactory factory = SAXParserFactory.newInstance();
            factory.setValidating(false);
            factory.setNamespaceAware(false);
            SAXParser          parser  = factory.newSAXParser();
            WelcomeFileHandler handler = new WelcomeFileHandler();
            InputStream        is      =
                _context.getResourceAsStream("WEB-INF/web.xml");
            if (is == null)
            {
                _context.log("Unable to get inputstream for web.xml");
            }
            parser.parse(is, handler);
            _welcomeFiles = handler.getWelcomeFiles();
            _context.log("Number of welcome files: " + _welcomeFiles.length);
        }
        catch (Exception ex)
        {
            throw new ServletException(ex);
        }
}

During the init method, we have to get any predefined welcome files for the current ServletContext.