Front Controller Design Pattern

index.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

<title>Home Page</title>
</head>
<body>

<a href="StudentView.do">Show Student</a>

</body>
</html>

package design;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public interface Command {
 String execute(HttpServletRequest request,HttpServletResponse response);
}

package design;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class StudentViewCommand implements Command {

@Override
public String execute(HttpServletRequest request, HttpServletResponse response) {

 String page=null;
 StudentVO studentVo=null;
	 
 //query data using delegate and dao populate in Value Object
 studentVo=new StudentVO(1,"Ashok");

 request.setAttribute("student", studentVo);
 page="showStudent";
	 
 return page;
}


}

package design;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class FrontController extends HttpServlet {

 private static final long serialVersionUID = 1L;

@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
		                                  throws ServletException, IOException{

 String page=null;
 Command command=null;
 String requestUri=null;
 CommandHelper helper=null;
 Dispatcher dispatcher=null;

 requestUri=request.getRequestURI();
 helper=new CommandHelper();
 System.out.println("Request URI : "+requestUri);
 command=helper.getCommand(requestUri);
 
 page=command.execute(request, response);

 dispatcher=new Dispatcher();
 dispatcher.dispatch(request, response, page);
 }
}

package design;

public class CommandHelper {

 public Command getCommand(String uri) {
   if(uri.contains("StudentView.do")){
	   return new StudentViewCommand();
   }
   
   return null;
 }

}

package design;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Dispatcher {

 public void dispatch(HttpServletRequest request, HttpServletResponse response, String page) {

 RequestDispatcher dispatcher=null;
 if(page!=null){
  dispatcher=request.getRequestDispatcher(mapPageToView(page));
   try{
	  dispatcher.forward(request, response);
   }catch(ServletException e){
	   e.printStackTrace();
   }catch (IOException e) {
	   e.printStackTrace();
   }
 }//if
	 
 }

private String mapPageToView(String page) {
  
  if(page.equals("showStudent")){
	 return "viewStudent.jsp";
  }

  return null;
}

}

package design;

public class StudentVO {

 private int id;
 private String name;
 
 public StudentVO(int id, String name){
	this.id=id;
	this.name=name;
 }

 //setters and getters
 
public int getId() {
	return id;
}
public void setId(int id) {
	this.id = id;
}

public String getName() {
	return name;
}
public void setName(String name) {
	this.name = name;
}
 
}

viewStudent.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>

<jsp:useBean id="student" type="design.StudentVO" scope="request" beanName="studentVO"/>


<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Student Information</title>
</head>
<body>

<p style="color: blue;font-size: large;font-family: sans-serif;">
Student Id : <jsp:getProperty property="id" name="student"/><br>
Student Name : <jsp:getProperty property="name" name="student"/>
</p>

</body>
</html>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   
xmlns="http://java.sun.com/xml/ns/javaee"   
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"   
id="WebApp_ID" version="3.0">  
  
<servlet>
 <servlet-name>front</servlet-name>
 <servlet-class>design.FrontController</servlet-class>
</servlet>
<servlet-mapping>
 <servlet-name>front</servlet-name>
 <url-pattern>*.do</url-pattern>
</servlet-mapping>

<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
 
</web-app>

result :

http://localhost:8001/javaT/

http://localhost:8001/javaT/StudentView.do

browser :
Student Id : 1
Student Name : Ashok

console :
Request URI : /javaT/StudentView.do

BACK