Servlet Annotations in Java (@WebServlet) – Beginner’s Guide

Introduction

Earlier, Java Servlets were configured using the web.xml deployment descriptor.
While powerful, web.xml often became large, complex, and hard to maintain.

To simplify servlet configuration, Servlet Annotations were introduced—especially the @WebServlet annotation.

This lesson explains:

What servlet annotations are
What @WebServlet does
How to use it step by step
Why it is preferred in modern Java web development

No prior knowledge of annotations is required.

What Are Servlet Annotations?

Simple Definition:

Servlet annotations are special Java tags used to configure servlets directly in the Java class, without using web.xml.

In simple words:

Annotations replace XML configuration with readable Java code.

What Is @WebServlet?

Definition:

@WebServlet is an annotation used to define and map a servlet to a URL.

📌 It tells the servlet container:

This class is a servlet
Which URL should trigger it

Why Use @WebServlet?

Problems with `web.xml`

Large XML files
Hard to read
Configuration separate from code
Error-prone

Benefits of `@WebServlet`

Less configuration
Easy to understand
Cleaner code
Faster development
Preferred in modern applications

Most new projects use annotations instead of web.xml.

Basic Syntax of @WebServlet

@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
}

This maps the servlet to:

http://localhost:8080/YourApp/hello

Complete Example Using @WebServlet

package com.example.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

@WebServlet("/welcome")
public class WelcomeServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response)
                         throws IOException {

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<h1>Welcome! Servlet Annotation is working.</h1>");
    }
}

How @WebServlet Works (Behind the Scenes)

Tomcat Server Starts
       ↓
Scans Servlet Classes
       ↓
Finds @WebServlet Annotation
       ↓
Registers URL Mapping
       ↓
Servlet Ready to Handle Requests

No need to write mapping in web.xml.

Using Multiple URL Patterns

@WebServlet(urlPatterns = {"/login", "/signin"})
public class LoginServlet extends HttpServlet {
}

Same servlet can respond to multiple URLs.

Important Attributes of @WebServlet

Attribute	Purpose
`urlPatterns`	Defines servlet URL
`name`	Logical servlet name
`loadOnStartup`	Loads servlet at startup
`initParams`	Initialization parameters

Example: `loadOnStartup`

@WebServlet(urlPatterns = "/init", loadOnStartup = 1)
public class InitServlet extends HttpServlet {
}

Servlet loads when server starts, not on first request.

Example: `initParams`

@WebServlet(
    urlPatterns = "/config",
    initParams = {
        @WebInitParam(name = "admin", value = "true")
    }
)
public class ConfigServlet extends HttpServlet {
}