Servlet HTTP Methods

HTTP Methods in Servlets

HttpServlet provides a separate method for each HTTP verb. You override only the methods your Servlet needs to handle:

Method	HTTP Verb	Use Case
`doGet()`	GET	Retrieve data, display pages
`doPost()`	POST	Submit forms, create resources
`doPut()`	PUT	Update/replace a resource
`doDelete()`	DELETE	Delete a resource
`doHead()`	HEAD	Like GET but no response body
`doOptions()`	OPTIONS	Returns supported HTTP methods
`doPatch()`	PATCH	Partial update (override service())

doGet and doPost

package com.example;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.WebServlet;
import java.io.*;

@WebServlet("/form")
public class FormServlet extends HttpServlet {

    // GET: Show the form
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE html><html><body>");
        out.println("<h2>Registration Form</h2>");
        out.println("<form method='post' action='/form'>");
        out.println("  Name: <input type='text' name='name'/><br/>");
        out.println("  Email: <input type='email' name='email'/><br/>");
        out.println("  <button type='submit'>Register</button>");
        out.println("</form></body></html>");
    }

    // POST: Process the form
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        String name  = req.getParameter("name");
        String email = req.getParameter("email");

        // Validate
        if (name == null || name.trim().isEmpty()) {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, "Name is required");
            return;
        }

        // Process (save to DB, etc.)
        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter out = resp.getWriter();
        out.println("<h2>Registration Successful!</h2>");
        out.println("<p>Name: " + name + "</p>");
        out.println("<p>Email: " + email + "</p>");
    }
}

HTTP Status Codes

Code	Constant	Meaning
200	SC_OK	Success
201	SC_CREATED	Resource created
301	SC_MOVED_PERMANENTLY	Permanent redirect
302	SC_FOUND	Temporary redirect
400	SC_BAD_REQUEST	Invalid request
401	SC_UNAUTHORIZED	Authentication required
403	SC_FORBIDDEN	Access denied
404	SC_NOT_FOUND	Resource not found
500	SC_INTERNAL_SERVER_ERROR	Server error

sendRedirect vs RequestDispatcher.forward

@WebServlet("/redirect-demo")
public class RedirectServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {

        String action = req.getParameter("action");

        if ("redirect".equals(action)) {
            // sendRedirect: client-side redirect (new HTTP request)
            // URL changes in browser, request attributes are lost
            // Can redirect to external URLs
            resp.sendRedirect("https://example.com");
            // OR: resp.sendRedirect(req.getContextPath() + "/home");

        } else if ("forward".equals(action)) {
            // RequestDispatcher.forward: server-side forward (same request)
            // URL does NOT change in browser, request attributes are preserved
            // Can only forward within the same web application
            req.setAttribute("message", "Forwarded from RedirectServlet");
            RequestDispatcher rd = req.getRequestDispatcher("/WEB-INF/views/result.jsp");
            rd.forward(req, resp);

        } else if ("include".equals(action)) {
            // RequestDispatcher.include: includes another resource's output
            // Both servlets contribute to the response
            RequestDispatcher rd = req.getRequestDispatcher("/header.jsp");
            rd.include(req, resp);
            resp.getWriter().println("<p>Main content here</p>");

        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, "Unknown action");
        }
    }
}

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Servlet HTTP Methods

HTTP Methods in Servlets

HTTP Status Codes

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