Servlet Architecture

Servlet Architecture defines how Java web applications handle client requests and generate dynamic responses using server-side components called servlets. It works on a request-response model where the web server interacts with servlets through a servlet container. This architecture ensures efficient processing, scalability, and platform independence for web applications.

• Manages the lifecycle of servlets, including loading, initialization, execution, and destruction.
• Handles client requests (HttpServletRequest) and sends responses (HttpServletResponse).
• Important methods include init(), service(), and destroy() which control servlet execution.

Real world example: When a user clicks the “Buy Now” button on an online shopping website, the browser sends a request to the server, which is handled by a servlet. The servlet processes the request by checking product details and placing the order, then sends a confirmation response back to the user.

Key Components of Servlet Architecture

Servlet Architecture consists of the following main components:

Servlet Architecture Flow (Step-by-Step):

1. Client (Web Browser)

• The client is usually a web browser (Chrome, Firefox, Edge, etc.)
• It sends an HTTP request to the web server
• Example requests: Submitting a form, clicking a link, and sending JSON data.

2. Web Server

• The web server receives client requests
• It forwards dynamic requests (Servlet/JSP) to the web container
• Handles static resources like HTML, CSS, JS, and images.
• Examples of Web Servers: Apache Tomcat, Jetty.

3. Web Container (Servlet Container)

The web container is responsible for managing servlets. Responsibilities of Web Container

• Loads and initializes servlets
• Manages servlet lifecycle
• Maps URLs to servlets
• Handles multithreading
• Provides request and response objects
• Manages security and sessions

4. Servlet

A servlet is the core component that:

• Processes client requests
• Contains business logic
• Generates responses (HTML, JSON, XML)

Servlets typically extend:

HttpServlet

5. Request and Response Objects

1. HttpServletRequest:

• Holds client request data
• Parameters, headers, cookies, session data

2. HttpServletResponse:

• Used to send response back to client
• HTML, JSON, status codes, headers

Related Article: Servlet Lifecycle

Example of Servlet Architecture

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class HelloServlet extends HttpServlet {

    public void init() throws ServletException {
        // Initialization code
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        
        out.println("<h2>Hello, Welcome to Servlet Architecture!</h2>");
    }

    public void destroy() {
        // Cleanup code
    }
}

Code Explanation:

• The browser sends a request to HelloServlet.
• The web container loads and initializes the servlet.
• The doGet() method processes the request.
• The servlet generates an HTML response.
• The response is sent back to the browser.