☕ Introduction to Java Servlets

Java Servlets are server-side Java programs used to handle requests and responses in web applications. They are part of the Java EE (Enterprise Edition) platform and run inside a Servlet container like Apache Tomcat.

📌 What is a Servlet?

A Servlet is a Java class that:

Runs on a server

Receives HTTP requests (like from a web form)

Processes the request (e.g., reads data, talks to a database)

Sends back an HTTP response (like HTML or JSON)

It acts like a bridge between a web browser (client) and the Java backend (server logic).

⚙️ How Servlets Work

Here’s a simple flow:

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Browser (Client)

    ↓

  HTTP Request

    ↓

Servlet Container (e.g., Tomcat)

    ↓

Servlet (Processes the request)

    ↓

  HTTP Response (HTML, JSON, etc.)

    ↓

Browser (Displays result)

🧱 Servlet Lifecycle

A servlet follows a well-defined lifecycle managed by the servlet container:

Initialization (init() method) — Called once when the servlet is first loaded.

Request Handling (doGet() or doPost()) — Called for each client request.

Destruction (destroy() method) — Called when the servlet is removed from memory.

📄 Basic Servlet Example (Java)

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import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class HelloServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

        throws ServletException, IOException {

        response.setContentType("text/html");

        PrintWriter out = response.getWriter();

        out.println("<h1>Hello from Java Servlet!</h1>");

    }

}

🛠️ Deploying a Servlet

Package your servlet in a .war (Web Application Archive) file.

Deploy it to a Servlet container (like Apache Tomcat).

Configure it in web.xml or use annotations (@WebServlet).

Example with annotation:

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@WebServlet("/hello")

public class HelloServlet extends HttpServlet {

    // ...

}

Now you can access it in the browser at:

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http://localhost:8080/yourapp/hello

✅ Why Use Servlets?

Build dynamic web content using Java

Control over HTTP request/response flow

Extendable and integrates with frameworks (like JSP, Spring)

Portable across any Java EE-compliant server

🔄 Servlet vs JSP vs Spring

Technology Purpose

Servlet Backend logic (Java code)

JSP View layer (HTML with Java)

Spring MVC Full-featured web framework

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