Front Controller Pattern

A Front Controller Pattern says that if you want to provide the centralized request handling mechanism so that all the requests will be handled by a single handler”. This handler can do the authentication or authorization or logging or tracking of request and then pass the requests to corresponding handlers.

Usage:

When you want to control the page flow and navigation.
When you want to access and manage the data model.
When you want to handle the business processing.

Benefits:

It reduces the duplication of code in JSP pages, especially in those cases where several resources require the same processing.
It maintains and controls a web application more effectively.
A web application of two-tier architecture, the recommended approach is front controller to deal with user requests.

UML for Front Controller Pattern:

Front Controller Pattern

Implementation of Front Controller Pattern:

Step 1

Create a Login.html web page.

  <html>  <head>  <title>  Login page  </title>  </head>  <body style=”color:green;”>  <h1 style=”font-family:Comic Sans Ms;text-align=”center”;font-size:20pt;  color:#00FF00;>  Login Page  </h1>  <form method=”POST” action=”FrontControllerServlet” onsubmit=”return checkForm(this);”>  <p>Username: <input type=”text” name=”username”></p>  <p>Password: <input type=”password” name=”pwd1″></p>  <p>Confirm Password: <input type=”password” name=”pwd2″></p>  <p><input type=”submit” value=”Login”></p>  </form>  <script type=”text/javascript”>      function checkForm(form)    {      if(form.username.value == “”) {        alert(“Error: Username cannot be blank!”);        form.username.focus();        return false;      }      re = /^w+$/;      if(!re.test(form.username.value)) {        alert(“Error: Username must contain only letters, numbers and underscores!”);        form.username.focus();        return false;      }        if(form.pwd1.value != “” && form.pwd1.value == form.pwd2.value) {        if(form.pwd1.value.length < 6) {          alert(“Error: Password must contain at least six characters!”);          form.pwd1.focus();          return false;        }        if(form.pwd1.value == form.username.value) {          alert(“Error: Password must be different from Username!”);          form.pwd1.focus();          return false;        }  re = /[0-9]/;        if(!re.test(form.pwd1.value)) {          alert(“Error: password must contain at least one number (0-9)!”);          form.pwd1.focus();          return false;        }        re = /[a-z]/;        if(!re.test(form.pwd1.value)) {          alert(“Error: password must contain at least one lowercase letter (a-z)!”);          form.pwd1.focus();          return false;        }        re = /[A-Z]/;        if(!re.test(form.pwd1.value)) {          alert(“Error: password must contain at least one uppercase letter (A-Z)!”);          form.pwd1.focus();          return false;        }      } else {        alert(“Error: Please check that you’ve entered and confirmed your password!”);        form.pwd1.focus();        return false;      }      return true;    }    </script>  </body>  </html>  

Step 2

Create a FrontControllerServlet.java class which is a servlet and it may be a JSP page also.

  package controller;    import java.io.IOException;  import java.io.PrintWriter;    import javax.servlet.RequestDispatcher;  import javax.servlet.ServletException;  import javax.servlet.annotation.WebServlet;  import javax.servlet.http.HttpServlet;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse;    /**   * Servlet implementation class FrontControllerServlet   */  @WebServlet(“/FrontControllerServlet”)  public class FrontControllerServlet extends HttpServlet {    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {                     response.setContentType(“text/html”);        PrintWriter out = response.getWriter();      String username=request.getParameter(“username”);  String password=request.getParameter(“pwd2”);    if (password.equals(“Ashwani1987”)) {    RequestDispatcher rd=request.getRequestDispatcher(“/Success.jsp”);  rd.forward(request, response);  } else {    RequestDispatcher rd=request.getRequestDispatcher(“/Error.jsp”);  rd.forward(request, response);  }    }    }  

Step 3

Create a Success.jsp page.

  <%@ 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>Welcome Page</title>  </head>  <body style=”background-color: gray;”>       <%  String name=request.getParameter(“username”); %>        <b>Welcome,</b> <% out.print(name); %>    </body>  </html>  

Step 4

Create a Error.jsp page.

  <%@ 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>Insert title here</title>  </head>  <body style=”background-color: olive;”>        <b>You are have entered wrong username or password!!</b><br>        <a href=”../Login.html”>Back To Home Page</a>  </body>  </html>  

Step 5

Create a web.xml file.

  <?xml version=”1.0″ encoding=”UTF-8″?>  <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” version=”3.0″>    <display-name>Front Controller Example</display-name>    <welcome-file-list>      <welcome-file>Login.html</welcome-file>    </welcome-file-list>  </web-app>  

Output:

Front Controller Pattern

Download this Example

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Front Controller Pattern

Front Controller Pattern

Usage:

Benefits:

UML for Front Controller Pattern:

Implementation of Front Controller Pattern:

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