Add Front-Controller explanation

java-design-pattern-questions.md

@@ -2,6 +2,116 @@
 
 #### Q. Exaplain MVC, Front-Controller, DAO, DTO, Service-Locator, Prototype design patterns?
 
+**2. Front-Controller**
+
+The 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 type of design pattern.
+
+* Front Controller - Single handler for all kinds of requests coming to the application (either web based/ 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.
+
+Example:
+
+We are going to create a `FrontController` and `Dispatcher` to act as Front Controller and Dispatcher correspondingly. `HomeView` and `StudentView` represent various views for which requests can come to front controller.
+
+FrontControllerPatternDemo, our demo class, will use FrontController to demonstrate Front Controller Design Pattern.
+
+Step 1
+Create Views.
+
+*HomeView.java*
+```java
+public class HomeView {
+ public void show(){
+ System.out.println("Displaying Home Page");
+ }
+}
+```
+*StudentView.java*
+```java
+public class StudentView {
+ public void show(){
+ System.out.println("Displaying Student Page");
+ }
+}
+```
+
+Step2
+Create Dispatcher.
+
+*Dispatcher.java*
+```java
+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();
+ }
+ }
+}
+```
+
+Step3
+Create FrontController.
+
+*FrontController.java*
+```java
+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 the user
+ if(isAuthenticUser()){
+ dispatcher.dispatch(request);
+ }
+ }
+}
+```
+
+Step4
+Use the FrontController to demonstrate Front Controller Design Pattern.
+
+*FrontControllerPatternDemo.java*
+```java
+public class FrontControllerPatternDemo {
+ public static void main(String[] args) {
+
+ FrontController frontController = new FrontController();
+ frontController.dispatchRequest("HOME");
+ frontController.dispatchRequest("STUDENT");
+ }
+}
+```
+
 *ToDo*
 
 ## Q. What are the design patterns available in Java?
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