Front Controller design pattern is used to provide a centralized request handling mechanism so that all requests will be handled by a single handler. This handler can do the authentication/authorization logging or tracking of request and then pass the requests to corresponding handlers. Following are the entities of this design pattern :

• Front Controller – Single handler for all kinds of requests coming to the application (web or desktop based)
• Dispatcher – Front Controller may use a dispatcher object which can dispatch the request to corresponding specific handler
• View – Views are the object for which the requests are made

An example below shows the use of Front Controller design pattern.

Step 1 : Create Views

public class HomeView {
    public void show(){
        System.out.println("Displaying Home Page");
    }
}

public class StudentView {
    public void show(){
        System.out.println("Displaying Student Page");
    }
}

Step 2 : Create Dispatcher

public class Dispatcher {
    private StudentView studentView;
    private HomeView homeView;

    public Dispatcher() {
        studentView = new StudentView();
        homeView = new HomeView();
    }

    public void dispatch(String request) {
        if (request.equalsIgnoreCase("STUDENT")) {
            studentView.show();
        } else {
            homeView.show();
        }
    }
}

Step 3 : Create FrontController

public class FrontController {
    private Dispatcher dispatcher;

    public FrontController() {
        dispatcher = new Dispatcher();
    }

    private boolean isAuthenticUser() {
        System.out.println("User is authenticated successfully.");
        return true;
    }

    private void trackRequest(String request) {
        System.out.println("Page requested: " + request);
    }

    public void dispatchRequest(String request) {
        // log each request
        trackRequest(request);

        // authenticate user
        if (isAuthenticUser()) {
            dispatcher.dispatch(request);
        }
    }
}

Step 4 : Use the FrontController to demonstrate Front Controller Design Pattern

public class FrontControllerPatternDemo {
    public static void main(String[] args) {
        FrontController frontController = new FrontController();
        frontController.dispatchRequest("HOME");
        frontController.dispatchRequest("STUDent");
    }
}

The output will be :

Page requested: HOME
User is authenticated successfully.
Displaying Home Page
Page requested: STUDent
User is authenticated successfully.
Displaying Student Page