MVC with JSP

MVC Design Pattern

MVC (Model-View-Controller) is a software design pattern that separates an application into three interconnected components:

Model — Represents the data and business logic (JavaBeans, POJOs, DAO classes)
View — Presents data to the user (JSP pages)
Controller — Handles user requests and coordinates Model and View (Servlets)

In the JSP+Servlet MVC pattern: the browser sends a request to a Servlet (Controller), which processes it, interacts with the Model, and then forwards to a JSP (View) to render the response.

Model - User JavaBean

package com.example.model;

// Model: JavaBean representing a User
public class User {
    private String username;
    private String password;
    private String email;
    private String role;

    public User() {}

    public User(String username, String password, String email, String role) {
        this.username = username;
        this.password = password;
        this.email    = email;
        this.role     = role;
    }

    // Getters and Setters
    public String getUsername() { return username; }
    public void setUsername(String username) { this.username = username; }

    public String getPassword() { return password; }
    public void setPassword(String password) { this.password = password; }

    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }

    public String getRole() { return role; }
    public void setRole(String role) { this.role = role; }

    // Business logic method
    public boolean isAdmin() {
        return "admin".equalsIgnoreCase(role);
    }
}

Controller - LoginServlet

package com.example.controller;

import com.example.model.User;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.WebServlet;
import java.io.IOException;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {

    // Show login form (GET)
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Forward to login view
        RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/views/login.jsp");
        rd.forward(request, response);
    }

    // Process login form (POST)
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        String username = request.getParameter("username");
        String password = request.getParameter("password");

        // Validate credentials (in real app, check database)
        if ("admin".equals(username) && "password123".equals(password)) {
            // Create user model
            User user = new User(username, password, "admin@example.com", "admin");

            // Store in session
            HttpSession session = request.getSession();
            session.setAttribute("loggedUser", user);

            // Forward to welcome view
            RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/views/welcome.jsp");
            rd.forward(request, response);
        } else {
            // Set error message and forward back to login
            request.setAttribute("errorMsg", "Invalid username or password!");
            RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/views/login.jsp");
            rd.forward(request, response);
        }
    }
}

View - JSP Pages

View - Login and Welcome JSP

<%-- WEB-INF/views/login.jsp --%>
<%@ page language="java" contentType="text/html; charset=UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html>
<html>
<head>
    <title>Login</title>
    <style>
        .login-box { max-width:400px; margin:80px auto; padding:30px;
                     border:1px solid #ddd; border-radius:8px; }
        .error { color:red; margin-bottom:10px; }
        input { width:100%; padding:8px; margin:8px 0; box-sizing:border-box; }
        button { width:100%; padding:10px; background:#2196F3; color:#fff; border:none; cursor:pointer; }
    </style>
</head>
<body>
    <div class="login-box">
        <h2>Login</h2>
        <c:if test="${not empty errorMsg}">
            <p class="error">${errorMsg}</p>
        </c:if>
        <form action="${pageContext.request.contextPath}/login" method="post">
            <input type="text" name="username" placeholder="Username" required/>
            <input type="password" name="password" placeholder="Password" required/>
            <button type="submit">Login</button>
        </form>
    </div>
</body>
</html>

<%-- WEB-INF/views/welcome.jsp --%>
<%@ page language="java" contentType="text/html; charset=UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%-- Protect this page: redirect if not logged in --%>
<c:if test="${empty sessionScope.loggedUser}">
    <c:redirect url="/login"/>
</c:if>
<!DOCTYPE html>
<html>
<head><title>Welcome</title></head>
<body>
    <h1>Welcome, ${sessionScope.loggedUser.username}!</h1>
    <p>Email: ${sessionScope.loggedUser.email}</p>
    <p>Role: ${sessionScope.loggedUser.role}</p>
    <c:if test="${sessionScope.loggedUser.admin}">
        <p><a href="admin.jsp">Go to Admin Panel</a></p>
    </c:if>
    <p><a href="${pageContext.request.contextPath}/logout">Logout</a></p>
</body>
</html>

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MVC with JSP

MVC Design Pattern

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