Introduction to Servlets:

  • Java servlets are small, platform-independent Java programs that can be used to extend the functionality of a Web server in variety of ways.
  • Small java programs compiled to bytecode that can be loaded dynamically and that extends the capabilities of the host.
  •  A client program , which could be a web browser or some other program that can make connections across the internet, accesses a web server and makes a request.
  • This request is processed by the servlet engine that runs with the web server , which returns response to a servlet.
  • the servlet in turn sends a response in HTTP form to the client.
  • In functionality servlets lie somewhere between Common Gateway Interface (CGI) programs.

What is Servlet? 

  •  Servlet is a java based web technology to develop server side programs to make a web site interactive.
  • Servlet is an API.
  • A collection of library interfaces and classes of two pavkages is nothing but servlet API.
  • javax.servlet.
  • javax.servlet.http
  • A collection of library methods of above two packages is nothing but servlet API.
  • Servlet is specification.
  • Servlet is a J2EE technology.

A Servlet is a Java programming language class that extends the capabilities of a server to handle client requests and generate dynamic web content. Servlets form the foundation of Java-based web development and are essential for common operations like login systems, form processing, and session management.

In this tutorial, you'll learn how to set up, create, and deploy Servlets while understanding key concepts like HTTP methods, session management, and more.

Prerequisites

Before you dive in, make sure you have:

  1. Basic knowledge of Java programming.
  2. JDK (Java Development Kit) installed.
  3. A web server like Apache Tomcat.
  4. An IDE (Eclipse, IntelliJ, or NetBeans).
  5. Familiarity with HTML and web concepts (optional but helpful).

Setting Up Your Servlet Project

Step 1: Create a Dynamic Web Project

  1. In your IDE (e.g., Eclipse), create a Dynamic Web Project.
  2. Name it ServletDemo and configure Tomcat as the runtime server.

Step 2: Add Servlet Dependencies

For Maven projects, add the javax.servlet dependency into your pom.xml file:

<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>javax.servlet-api</artifactId>
  <version>4.0.1</version>
  <scope>provided</scope>
</dependency>

Creating Your First Servlet

Let's build a simple "Hello World" Servlet.

Step 1: Create a Servlet Class

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("<html><body>");
        out.println("<h1>Hello, World! This is my first Servlet.</h1>");
        out.println("</body></html>");
    }
}

Step 2: Configure Servlet Mapping

In web.xml (or, for modern setups, use annotations):

<servlet>
  <servlet-name>HelloServlet</servlet-name>
  <servlet-class>HelloServlet</servlet-class>
</servlet>

<servlet-mapping>
  <servlet-name>HelloServlet</servlet-name>
  <url-pattern>/hello</url-pattern>
</servlet-mapping>

Alternatively, use annotations in the Servlet class:

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

Step 3: Deploy and Test

  1. Deploy the project to Tomcat.
  2. Visit http://localhost:8080/ServletDemo/hello to see the output!

Handling Different HTTP Methods

Servlets can handle different HTTP request types using methods such as doGet() and doPost().

Example: Handling a POST Request

protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    String username = request.getParameter("username");
    response.getWriter().println("Welcome, " + username + "!");
}

An HTML Form to Test the POST Request:

<form action="hello" method="post">
  <input type="text" name="username">
  <input type="submit" value="Submit">
</form>

Important Servlet Concepts

  1. Request and Response Objects:

    • HttpServletRequest: Contains client request data (parameters, headers).
    • HttpServletResponse: Sends data back to the client.
  2. Session Management:
    Use HttpSession to track user sessions:

    HttpSession session = request.getSession();
    session.setAttribute("user", "John");
    
  3. Request Dispatching:
    Forward requests to other resources:

    RequestDispatcher dispatcher = request.getRequestDispatcher("welcome.jsp");
    dispatcher.forward(request, response);
    
  4. Filters:
    Intercept requests/responses for logging, authentication, etc.

Servlet Development Best Practices

  1. Separation of Concerns: Keep business logic separate from presentation (use JSP or MVC frameworks).
  2. Use Annotations: Simplify configuration with @WebServlet, @WebFilter, etc.
  3. Exception Handling: Implement error pages for uncaught exceptions.
  4. Security: Sanitize inputs, use HTTPS, and manage sessions securely.


Servlets are a powerful tool in Java web development. Learning them provides a strong foundation for working with advanced frameworks like Spring MVC or Jakarta EE. Start by experimenting with small projects, session management, and later integrate databases to build full-stack applications.

read more

Next Steps

  • Explore JSP (JavaServer Pages) for dynamic views.
  • Learn about Servlet Context and Listeners.
  • Dive into Spring Boot for modern web development..

Instance Of Java

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