Week 8: Mar 16 - Mar 22, 2026

Unit III: Servlets & JSP Introduction

Week Overview

This week introduces server-side programming with Servlets and Java Server Pages (JSP), covering architecture, lifecycle, and request/response handling.

Course Outcome: CO-3 (K3 - Application)
Duration: 1 week (4 lectures + 1 lab)
Lab: Servlet Development
Assignment 3 Due: Mar 18

Quick Practice Quizzes (Lectures 21-24)

Planned for this week. Use the Quiz Hub for currently available quizzes.

Lecture Materials

This week uses upcoming lecture decks. Use the Lectures Index for all available slides.

Lecture 21: Servlet Architecture & Lifecycle

Lecture Materials

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What is a Servlet?

Java program that runs on web server
Receives HTTP requests and sends responses
Extends HttpServlet class
Part of Java EE standard

Servlet Lifecycle

1. Loading: Server loads servlet class
2. Instantiation: Creates servlet object
3. Initialization: Calls init() method (once)
4. Service: Calls service() method (each request)
   - Calls doGet() or doPost() based on HTTP method
5. Destruction: Calls destroy() method (when unloading)

Basic Servlet Structure

import javax.servlet.*;
import javax.servlet.http.*;

public class FirstServlet extends HttpServlet {
  
  // Initialization
  public void init() throws ServletException {
    System.out.println("Servlet initialized");
  }
  
  // Handle GET requests
  protected void doGet(HttpServletRequest request, 
                      HttpServletResponse response)
    throws ServletException, IOException {
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    out.println("<h1>Welcome</h1>");
    out.close();
  }
  
  // Cleanup
  public void destroy() {
    System.out.println("Servlet destroyed");
  }
}

Servlet Configuration

<!-- web.xml -->
<servlet>
  <servlet-name>FirstServlet</servlet-name>
  <servlet-class>com.example.FirstServlet</servlet-class>
</servlet>

<servlet-mapping>
  <servlet-name>FirstServlet</servlet-name>
  <url-pattern>/hello</url-pattern>
</servlet-mapping>

Lecture 22: HTTP GET & POST Requests

Lecture Materials

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Request/Response Cycle

Client Request → Web Server → Servlet → Database
Client ← Web Server ← Response ← Servlet ← Data

GET Requests

protected void doGet(HttpServletRequest request, 
                    HttpServletResponse response) {
  // Get query parameters
  String name = request.getParameter("name");
  String email = request.getParameter("email");
  
  // Send response
  response.getWriter().println("Name: " + name);
}

Characteristics: - Data in URL query string - Limited data size - Bookmarkable - Not secure - Caching-friendly

POST Requests

protected void doPost(HttpServletRequest request,
                     HttpServletResponse response) {
  // Get form parameters
  String username = request.getParameter("username");
  String password = request.getParameter("password");
  
  // Process and respond
  response.getWriter().println("Login attempt");
}

Characteristics: - Data in request body (hidden) - Large data capacity - Not bookmarkable - More secure - No caching

Request/Response Objects

// Request methods
String method = request.getMethod();           // GET, POST, etc.
String path = request.getRequestURI();
String query = request.getQueryString();
String[] values = request.getParameterValues("item");
Map<String, String[]> params = request.getParameterMap();

// Response methods
response.setContentType("text/html; charset=UTF-8");
response.setStatus(HttpServletResponse.SC_OK);
PrintWriter out = response.getWriter();
out.println("Response content");

Lecture 23: Session Tracking & Cookies

Lecture Materials

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Sessions

// Create/Get session
HttpSession session = request.getSession();

// Store data
session.setAttribute("userId", "12345");
session.setAttribute("username", "john");

// Retrieve data
String userId = (String) session.getAttribute("userId");

// Session management
session.getCreationTime();
session.getMaxInactiveInterval();
session.invalidate();  // Logout

Cookies

// Create cookie
Cookie cookie = new Cookie("username", "john");
cookie.setMaxAge(60 * 60 * 24);  // 1 day
response.addCookie(cookie);

// Read cookie
Cookie[] cookies = request.getCookies();
for (Cookie cookie : cookies) {
  if (cookie.getName().equals("username")) {
    String value = cookie.getValue();
  }
}

// Delete cookie
Cookie cookie = new Cookie("username", "");
cookie.setMaxAge(0);
response.addCookie(cookie);

Differences

Session	Cookie
Server-side	Client-side
Secure	Less secure
Temporary	Persistent
Per user	Per browser
Lost on logout	Survives logout

Lecture 24: Introduction to JSP

Lecture Materials

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What is JSP?

Java Server Pages
Simplified Servlet technology
Mixes HTML and Java code
Converted to Servlet at runtime

JSP Page Structure

<%@ page language="java" contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<!DOCTYPE html>
<html>
<head>
  <title>My JSP Page</title>
</head>
<body>
  <h1>Welcome</h1>
  
  <!-- Expression -->
  <p>Current time: <%= java.time.LocalDateTime.now() %></p>
  
  <!-- Scriptlet -->
  <% 
    String name = request.getParameter("name");
    out.println("Hello, " + name);
  %>
  
  <!-- Declaration -->
  <%! 
    public String formatDate(Date date) {
      return new SimpleDateFormat("yyyy-MM-dd").format(date);
    }
  %>
</body>
</html>

JSP Elements

Expression (<%= %>): Outputs value to page
Scriptlet (<% %>): Java code execution
Declaration (<%! %>): Method/variable declaration
Directive (<%@ %>): Page configuration
Comment (<%-- --%>): JSP-only comment

Lab 8: Servlet Development

Objectives

Create functional servlets
Handle GET/POST requests
Manage sessions
Basic JSP pages

Activities

Create login servlet
Implement form processing
Add session management
Create simple JSP page
Deploy to application server

Deliverables

Working servlet application
Functional login system
Session management

Key Takeaways

✅ Servlets run on server and process requests
✅ Lifecycle manages servlet creation/destruction
✅ GET for safe, bookmarkable requests
✅ POST for secure data submission
✅ Sessions track user across requests
✅ JSP simplifies server-side programming

Next Week

Unit III continues: - JSP implicit objects and directives - JSTL (JSP Standard Tag Library) - MVC architecture - Database connectivity