How do I handle GET and POST requests in Jakarta Servlets?

Handling GET and POST requests in Jakarta Servlets involves overriding the doGet() and doPost() methods provided by the HttpServlet class. Here’s a step-by-step guide:

1. Import Necessary Packages

First, ensure you import the jakarta.servlet and jakarta.servlet.http packages in your servlet class.

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

2. Create a Servlet Class

Your servlet class should extend the HttpServlet class. The doGet() method will handle GET requests, while the doPost() method will handle POST requests.

3. Override `doGet` and `doPost` Methods

Use the HttpServletRequest object to get request data.
Use the HttpServletResponse object to send a response to the client.

4. Example Code

Here’s a complete example:

package org.kodejava.servlet;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/example")  // Annotation to map this servlet to "/example"
public class ExampleServlet extends HttpServlet {

    // Handles GET requests
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Set response content type
        response.setContentType("text/html");

        // Get query parameter (e.g., ?name=John)
        String name = request.getParameter("name");

        // Prepare response
        PrintWriter out = response.getWriter();
        out.println("<html><body>");
        out.println("<h1>Hello, " + (name != null ? name : "Guest") + "!</h1>");
        out.println("<form method='POST' action='/example'>");
        out.println("<label for='postName'>Enter your name:</label>");
        out.println("<input type='text' id='postName' name='name'>");
        out.println("<button type='submit'>Submit</button>");
        out.println("</form>");
        out.println("</body></html>");
    }

    // Handles POST requests
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Set response content type
        response.setContentType("text/html");

        // Get form data (e.g., from POST body)
        String name = request.getParameter("name");

        // Prepare response
        PrintWriter out = response.getWriter();
        out.println("<html><body>");
        out.println("<h1>Thank you, " + (name != null ? name : "Guest") + "!</h1>");
        out.println("<a href='/example'>Go back</a>");
        out.println("</body></html>");
    }
}

5. Explanation

Annotations: The @WebServlet("/example") annotation maps this servlet to the /example URL.
GET and POST
- The doGet() method handles requests sent as GET, typically used when the client fetches data.
- The doPost() method handles requests sent as POST, commonly used to send form data to the server.
Parameters: Use request.getParameter("paramName") to retrieve parameters from the request.

6. Deploy and Test

Add the servlet to your Jakarta EE web application.
Access the servlet:
- GET request: Open `http://localhost:8080/your-app-context/example` in a browser.
- POST request: Submit the HTML form created in doGet() or use a tool like Postman.

7. Keynotes

Always handle exceptions (IOException and ServletException) properly in production.
Use appropriate HTTP response headers and status codes.
Consider character encoding (request.setCharacterEncoding("UTF-8") and response.setCharacterEncoding("UTF-8")) for supporting special characters.

This is how you handle GET and POST requests in a Jakarta Servlet effectively!

Maven dependencies

<dependency>
    <groupId>jakarta.servlet</groupId>
    <artifactId>jakarta.servlet-api</artifactId>
    <version>6.1.0</version>
    <scope>provided</scope>
</dependency>