How do I implement a front controller in Java?

Question

I'm writing a very simple web framework using Java servlets for learning purposes. I've done this before in PHP, and it worked by consulting the request URI, then instantiating the appropriate class and method.

This worked fine in PHP, as one can do something like $c = new $x; $x->$y;. I'm unsure however of how to translate this to Java, or even if this is an appropriate way to go about it.

So far, I've tried:

Router router = new Router(request.getPathInfo());
String className = router.route(); //returns com.example.controller.Foo

Class c = Class.forName(className);
Object x = c.newInstance();

Foo y = (Foo) x;
y.doSomething();

This seems fine for a couple of routes, but doesn't seem like it would scale well, nor would it allow for sourcing routes from a configuration file.

How should I make it work?

Answer 1

I would use a Servlet Filter as Front Controller. The router would connect paths with request dispatchers. In the doFilter method you would convert ServletRequest to HttpServletRequest, extract the request path and match it against the registered mappings. The result of this mapping is a request dispatcher you would dispatch the request with.

In pseudo code:

doFilter(ServletRequest request, ServletResponse response) {
  httpServletRequest = (HttpServletRequest) request;
  path = httpServletRequest.getRequestURI();
  dispatcher = router.getTarget(path);
  dispatcher.dispatch(request, response);
}

Depending on your need the default routing mechanism of the Servlet API could be sufficient.