Front Controller pattern (Mediator pattern)

First, the Controller part should implement the Front Controller pattern (which is a specialized kind of Mediator pattern). It should consist of only a single servlet which provides a centralized entry point of all requests. It should create the Model based on information available by the request, such as the pathinfo or servletpath, the method and/or specific parameters. The Business Model is called Action in the below HttpServlet example.

protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

try {

Action action = ActionFactory.getAction(request);

String view = action.execute(request, response);

if (view.equals(request.getPathInfo().substring(1)) {

request.getRequestDispatcher("/WEB-INF/" + view + ".jsp").forward(request, response);

} else {

response.sendRedirect(view); // We'd like to fire redirect in case of a view change as result of the action (PRG pattern).

}

} catch (Exception e) {

throw new ServletException("Executing action failed.", e);

}

}

Executing the action should return some identifier to locate the view. Simplest would be to use it as filename of the JSP. Map this servlet on a specific url-pattern in web.xml, e.g. /pages/, .do or even just *.html.

In case of prefix-patterns as for example /pages/* you could then invoke URL's likehttp://example.com/pages/register, http://example.com/pages/login, etc and provide /WEB-INF/register.jsp, /WEB-INF/login.jsp with the appropriate GET and POST actions. The partsregister, login, etc are then available by request.getPathInfo() as in above example.

When you're using suffix-patterns like .do, .html, etc, then you could then invoke URL's likehttp://example.com/register.do, http://example.com/login.do, etc and you should change the code examples in this answer (also the ActionFactory) to extract the register and login parts by request.getServletPath() instead.