Java Servlets in Web Development

Published on: Apr 6th, 2025

What Are Java Servlets?

Java Servlets are server-side components that handle requests and responses in a web application. They are part of the Java EE (Enterprise Edition) specification and are used to create dynamic web content. When a user interacts with a web application, servlets process the request, perform any necessary business logic, and generate a response. They act as a bridge between the client (browser) and the server, allowing for dynamic content generation based on user input or other factors.

Why Use Servlets?

Servlets are a fundamental part of Java web applications. They provide a way to handle HTTP requests and responses, manage sessions, and interact with databases. While modern frameworks like Spring and JavaServer Faces (JSF) have largely replaced servlets for many developers, understanding servlets is crucial for grasping the underlying principles of Java web development.

  • Performance: Servlets are efficient and can handle multiple requests simultaneously.
  • Scalability: They can be easily scaled to handle increased load.
  • Integration: Servlets can be integrated with other Java technologies like JSP (JavaServer Pages) and EJB (Enterprise JavaBeans).
  • Control: They provide low-level control over request and response handling.
  • Session Management: Servlets can manage user sessions, allowing for personalized experiences.
  • Security: They can be configured to handle authentication and authorization.
  • Compatibility: Servlets are part of the Java EE specification, making them compatible with various Java application servers.

Basic Flow of a Servlet

When a user makes a request (e.g., via a form submission), the request is handled by the servlet, which processes the data, communicates with any databases or services as needed, and generates a response—usually HTML or JSON.

Here’s a simple example of a `doGet` method in a servlet:


                import java.io.IOException;
                import java.io.PrintWriter;
                import javax.servlet.ServletException;
                import javax.servlet.annotation.WebServlet;
                import javax.servlet.http.HttpServlet;
                import javax.servlet.http.HttpServletRequest;
                import javax.servlet.http.HttpServletResponse;
                
                @WebServlet("/hello")
                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!</h1>");
                        out.println("</body></html>");
                        out.close();
                    }
                }

In this example, when a user accesses the `/hello` URL, the servlet responds with a simple HTML page displaying "Hello, World!". The `doGet` method is called to handle GET requests, and you can also implement `doPost` for handling POST requests.

The servlet is annotated with `@WebServlet("/hello")`, which maps the servlet to the `/hello` URL. This is part of the Servlet 3.0 specification, which allows for annotation-based configuration. In older versions, servlets were configured in the `web.xml` file.

The servlet container (like Apache Tomcat) manages the lifecycle of servlets, including loading, instantiating, and invoking methods like `init()`, `service()`, and `destroy()`. This allows for efficient resource management and request handling.

Servlets can also handle sessions, allowing you to maintain user state across multiple requests. This is done using the `HttpSession` object, which can store user-specific data. For example, you can store user preferences or authentication tokens in the session.

Overall, servlets are a powerful tool for building dynamic web applications in Java. They provide a solid foundation for understanding how web applications work and can be used in conjunction with other Java technologies to create robust and scalable solutions.

Benefits and Use Cases

Java Servlets are still widely used in legacy systems and in teaching foundational web concepts. They are particularly useful when you want:

  • Full control over HTTP requests and responses
  • To manage sessions or authentication manually
  • To build lightweight web services without external frameworks

Conclusion

While servlets might not be the first tool in your toolbox in modern web development, understanding how they work is key to becoming a solid Java developer. They teach you the fundamentals of request handling, session management, and server-side rendering—all of which are concepts that remain important regardless of the stack you’re using.