Introduction to Java Servlets
Introduction
Java Servlets are fundamental to building dynamic, server-side web applications in the Java ecosystem. As Java’s standard for handling HTTP requests and responses, servlets provide a powerful way to create interactive websites, process forms, manage sessions, and build RESTful APIs. If you’re working with Java web technologies, understanding servlets is a crucial first step.
What is a Java Servlet?
A servlet is a Java class that runs on a server inside a servlet container (like Apache Tomcat, Jetty, or GlassFish). It extends the capabilities of servers by handling HTTP requests and generating dynamic responses, typically HTML or JSON.
When a client (browser or mobile app) sends an HTTP request to your web server, the server forwards the request to the appropriate servlet. The servlet processes the request, performs business logic, and sends a response back to the client.
Basic Servlet Lifecycle
A servlet goes through three main phases managed by the servlet container:
1️⃣ Initialization (init()) – Called once when the servlet is first loaded.
2️⃣ Request Handling (service() or doGet()/doPost()) – Called multiple times to handle incoming requests.
3️⃣ Destruction (destroy()) – Called once before the servlet is removed from memory, e.g., when the server shuts down or redeploys.
A Simple Example
Here’s a minimal servlet that responds with “Hello, World!”:
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, World!</h1>");
}
}
This servlet overrides doGet() to handle GET requests. When a client visits /HelloServlet, it returns an HTML page with “Hello, World!”.
Why Use Servlets?
✅ Performance: Lightweight and efficient; servlets remain in memory after initialization.
✅ Portability: Runs on any platform with a compatible servlet container.
✅ Extensibility: Easily integrates with other Java technologies (JSP, JDBC, Spring).
✅ Control: Gives fine-grained control over HTTP requests, responses, cookies, and sessions.
Conclusion
Java Servlets are the backbone of many enterprise web applications. They provide a fast, secure, and flexible way to build server-side logic, handle client requests, and generate dynamic content. Whether you’re building simple web forms or complex REST APIs, mastering servlets is key to unlocking the power of Java web development.
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