YourNote 301: Servlet

1. What is a Servlet?

A Servlet is a Java class that runs on a web server (e.g., Apache Tomcat) and handles HTTP requests.

Simple idea:

• Browser → sends request
• Servlet → processes request
• Servlet → sends response (HTML/JSON)

2. Servlet Lifecycle

Every servlet follows this lifecycle:

init() → service() → destroy()

Explanation:

• init() → runs once (initialization)
• service() → runs for every request
• destroy() → runs when server stops

3. Handling HTTP Requests

Servlets mainly deal with HTTP methods:

• doGet() → retrieve data
• doPost() → send data (forms)
• doPut() / doDelete() → advanced REST usage

Example:

protected void doGet(HttpServletRequest request, HttpServletResponse response)

4. Request & Response Objects

Two core objects:

HttpServletRequest

• Get user input
• Read parameters

String name = request.getParameter("name");

HttpServletResponse

• Send output to browser

response.getWriter().println("Hello " + name);

5. Servlet Mapping (URL Routing)

How URL connects to servlet:

Using Annotation (modern way)

@WebServlet("/hello")

Access via:

http://localhost:8080/hello

6. Working with JSP

• Servlet = logic
• JSP = presentation

Flow:

JSP (form) → Servlet (process) → JSP (display)

Example:

request.setAttribute("name", name);
request.getRequestDispatcher("result.jsp").forward(request, response);

7. Session Management

HTTP is stateless → Servlets manage sessions:

HttpSession session = request.getSession();
session.setAttribute("user", "Zhamri");

Used for:

• login systems
• shopping carts

8. Database Connection (JDBC)

Servlets often connect to database:

• MySQL / PostgreSQL / Oracle
• Use JDBC

Important for assignments:

• Insert data
• Retrieve data
• Display in JSP

9. Deployment & Server

Servlets need a server:

• Apache Tomcat (most common)
• Jetty / GlassFish