Applets vs Servlets in Java

Applets and Servlets are both Java technologies, but they serve very different purposes:

Applets

What is an Applet?

A Java program that runs in a web browser.
Meant for client-side execution.
Requires a Java plugin in the browser (now deprecated and unsupported by most browsers).

Characteristics:

Feature	Description
Execution	Runs on the client machine (browser).
GUI Support	Yes (Swing or AWT).
Use Case	Old-school interactive web UIs.
Security	Runs in a sandbox (restricted).
Obsolete?	✅ Yes. No longer supported by browsers.

Example:

import java.applet.Applet;
import java.awt.Graphics;

public class HelloApplet extends Applet {
    public void paint(Graphics g) {
        g.drawString("Hello from Applet!", 20, 20);
    }
}

Servlets

What is a Servlet?

A Java class that runs on a server and handles HTTP requests and responses.
Used to build web applications (server-side logic).
Forms the foundation for Spring MVC, JSP, and Java EE web apps.

Characteristics:

Feature	Description
Execution	Runs on the server (inside servlet container like Tomcat).
GUI Support	No GUI (sends HTML or data as response).
Use Case	Handling requests, processing forms, serving data.
Modern Usage	Backbone of Java web development.

Example:

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

public class HelloServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<h1>Hello from Servlet!</h1>");
    }
}

Applet vs Servlet Comparison Table

Feature	Applet	Servlet
Runs On	Client (Browser)	Server (Web container)
Purpose	GUI applications in browsers	Handle web requests/responses
GUI Support	Yes (AWT/Swing)	No (Returns HTML or data)
HTML Interaction	Embedded in HTML pages	Processes requests from HTML forms
Browser Support	Deprecated	Widely supported
Security	Runs in restricted sandbox	Server-side security (authentication etc.)
Modern Usage	Obsolete	Still heavily used (Spring Boot, JSP)