The **front controller [design pattern](https://www.educative.io/answers/design-patterns-in-java)** 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

#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;
}


class FrontControllerPattern {
	public static void main(String[] args) {
		Controller ctrl = new Controller();
		ctrl.forwardRequest("authentic", "pay bills");
	}
}

// Controller:
class Controller{
	private Dispatcher myDispatcher;
	
	public Controller(){
		myDispatcher = new Dispatcher();
	}
	public void forwardRequest(String u, String req) {
		if(authUser(u))
			myDispatcher.dispatch(req);
	}
	private boolean authUser(String user) {
		if(user.equalsIgnoreCase("authentic"))
			return true;
		else
			return false;
	}
}

// Dispatcher:
class Dispatcher{
	Handler1 handler1;
	Handler2 handler2;
	Handler3 handler3;
	
	Dispatcher(){
		handler1 = new Handler1();
		handler2 = new Handler2();
		handler3 = new Handler3();
	}
	public void dispatch(String req) {
		if(req.equalsIgnoreCase("pay bills"))
			handler1.updateView();
		else if(req.equalsIgnoreCase("update Username"))
			handler2.updateView();
		else if(req.equalsIgnoreCase("change password"))
			handler3.updateView();
		else
			System.out.println("Invalid request!");
	}
}

// Handlers:

class Handler1{
	View1 view1;
	
	public Handler1() {
		view1 = new View1();
	}
	public void updateView() {
		view1.update();
	}
}
class Handler2{
	View2 view2;
	
	public Handler2() {
		view2 = new View2();
	}
	public void updateView() {
		view2.update();
	}
}
class Handler3{
	View3 view3;
	
	public Handler3() {
		view3 = new View3();
	}
	public void updateView() {
		view3.update();
	}
}

// Views:

class View1{
	public void update() {
		System.out.println("Bills payed.");
	}
}
class View2{
	public void update() {
    System.out.println("Username updated.");
	}
}
class View3{
	public void update() {
    System.out.println("Password changed.");
	}
}

Java

What is the front controller design pattern?

The front controller design pattern is used to refine the structure of an application which:   Receives different types of requests from clients.   Authenticates clients.   Displays an output of the requests.   Parts of the pattern   The front controller receives a request from the client, authenticates it, and forwards the request to the dispatcher.   The dispatcher determines the type of the request and allocates it to the relevant handler.   The handler executes the business logic and updates the view.   The view is the front-end container of the result produced from the request.   UML diagram 

What is the front controller design pattern?

Parts of the pattern

UML diagram

Code