Start Servlet Setup Environment Create First Servlet

First Jakarta Servlet

A Jakarta Servlet 6.1 application runs inside a compatible servlet container. A servlet extends HttpServlet or implements Servlet, maps one or more URLs, and translates an HTTP request into a response. Application code now imports jakarta.servlet packages rather than the pre-Jakarta javax.servlet namespace.

Setup and Prerequisites

To develop Servlets you need:

JDK 8+ - Set JAVA_HOME environment variable
Apache Tomcat 9+ - Download from tomcat.apache.org
IDE - Eclipse EE or IntelliJ IDEA Ultimate
Servlet API JAR - jakarta.servlet-api-4.0.1.jar (provided by Tomcat, or add via Maven)

Maven pom.xml for Servlet Project

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>servlet-demo</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <dependencies>
        <!-- Servlet API (provided by Tomcat at runtime) -->
        <dependency>
            <groupId>jakarta.servlet</groupId>
            <artifactId>jakarta.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>
        <!-- JSP API -->
        <dependency>
            <groupId>jakarta.servlet.jsp</groupId>
            <artifactId>jakarta.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.2</version>
            </plugin>
        </plugins>
    </build>
</project>

First Servlet - HelloServlet

HelloServlet with Annotation Mapping

package com.example;

import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.WebServlet;
import java.io.*;

// @WebServlet annotation maps this servlet to /hello URL
// Servlet 3.0+ supports annotation-based configuration
@WebServlet(
    name = "HelloServlet",
    urlPatterns = {"/hello", "/greet"},
    loadOnStartup = 1
)
public class HelloServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        // Read init parameters from web.xml or @WebInitParam
        String greeting = config.getInitParameter("greeting");
        System.out.println("Init param greeting: " + greeting);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter out = resp.getWriter();

        String name = req.getParameter("name");
        if (name == null || name.trim().isEmpty()) name = "World";

        out.println("<!DOCTYPE html><html><body>");
        out.println("<h1>Hello, " + name + "!</h1>");
        out.println("<p>Request URI: " + req.getRequestURI() + "</p>");
        out.println("</body></html>");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // Delegate POST to GET handler
        doGet(req, resp);
    }
}

First Servlet - HelloServlet - XML Configuration

<!-- web.xml alternative to @WebServlet annotation -->
<web-app>
    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>com.example.HelloServlet</servlet-class>
        <init-param>
            <param-name>greeting</param-name>
            <param-value>Hello</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

Project Structure and Deployment

Build with Maven: mvn clean package - this creates a .war file in the target/ directory. Copy the WAR to Tomcat's webapps/ folder and start Tomcat. Access at http://localhost:8080/servlet-demo/hello?name=Alice.

Servlet Getting Started Project Structure

servlet-demo/
├── src/main/java/com/example/
│   └── HelloServlet.java
├── src/main/webapp/
│   ├── index.html
│   └── WEB-INF/
│       └── web.xml
└── pom.xml

Minimal Deployment

Use @WebServlet for a small explicit mapping or web.xml when deployment descriptors better centralize configuration. Build against the Servlet API supplied by the container rather than packaging a second copy. Set response status, content type, and character encoding before writing the body.

Keep the servlet thin: parse and validate HTTP input, call a service, and map the result. Do not put JDBC credentials, reusable business rules, or request-specific values in servlet instance fields. Verify the exact context path and mapping when a request returns 404.

Before you move on