What is the front controller design pattern?

The front controller design pattern is used to refine the structure of an application which:

  1. Receives different types of requests from clients.

  2. Authenticates clients.

  3. Displays an output of the requests.

Parts of the pattern

  1. The front controller receives a request from the client, authenticates it, and forwards the request to the dispatcher.

  2. The dispatcher determines the type of the request and allocates it to the relevant handler.

  3. The handler executes the business logic and updates the view.

  4. The view is the front-end container of the result produced from the request.

UML diagram

svg viewer

Code

#include <iostream>
using namespace std;
// Views:
class View1{
public:
    void update() {
        cout << "Bills payed." << endl;
    }
};
class View2{
public:
    void update() {
        cout << "Username updated." << endl;
    }
};
class View3{
public:
    void update() {
        cout << "Password changed." << endl;
    }
};
// Handlers:
class Handler1{
private:
    View1* view1;
    
public:
    Handler1() {
        view1 = new View1();
    }
    void updateView() {
        view1->update();
    }
};
class Handler2{
private:
    View2* view2;
    
public:
    Handler2() {
        view2 = new View2();
    }
    void updateView() {
        view2->update();
    }
};
class Handler3{
private:
    View3* view3;
    
public:
    Handler3() {
        view3 = new View3();
    }
    void updateView() {
        view3->update();
    }
};
// Dispatcher:
class Dispatcher{
private:
    Handler1* handler1;
    Handler2* handler2;
    Handler3* handler3;
    
public:
    Dispatcher(){
        handler1 = new Handler1();
        handler2 = new Handler2();
        handler3 = new Handler3();
    }
    void dispatch(string req) {
        if(req == "pay bills")
            handler1->updateView();
        else if(req == "update username")
            handler2->updateView();
        else if(req == "change password")
            handler3->updateView();
        else
            cout << "Invalid request!" << endl;
    }
};
// Controller:
class Controller{
private:
    Dispatcher* myDispatcher;
    bool authUser(string user) {
        if(user == "authentic")
            return true;
        else
            return false;
    }
public:
    Controller(){
        myDispatcher = new Dispatcher();
    }
    void forwardRequest(string u, string req) {
        if(authUser(u))
            myDispatcher->dispatch(req);
    }
};
int main(){
    Controller ctrl;
    ctrl.forwardRequest("authentic", "pay bills");
    
    return 0;
}

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