Servlet Request and Response Objects

HttpServletRequest and HttpServletResponse are the primary interfaces for reading client data and sending responses. Every Servlet method receives these two objects.

HttpServletRequest — Reading Data

getParameter("name") — Read form fields and query string values.
getParameterValues("hobby") — Read multi-value fields like checkboxes.
getHeader("User-Agent") — Read HTTP headers.
getSession() — Access or create an HTTP session.
getRequestDispatcher("/page.jsp").forward() — Forward to another resource.
getCookies() — Read cookies sent by the browser.

HttpServletResponse — Sending Data

setContentType("application/json") — Set MIME type.
setStatus(HttpServletResponse.SC_NOT_FOUND) — Set HTTP status code.
sendRedirect("/login") — Redirect browser to another URL.
addCookie(new Cookie("theme", "dark")) — Set cookies.
getWriter() — Get PrintWriter for text responses.
getOutputStream() — Get stream for binary data (images, files).

Practical Example

@WebServlet("/search")
public class SearchServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String query = req.getParameter("q");
        if (query == null || query.isBlank()) {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, "Missing query");
            return;
        }
        resp.setContentType("application/json");
        resp.getWriter().printf("{"query":"%s","results":[]}", query);
    }
}

Request Scope vs Session Scope

Use request attributes (req.setAttribute) for data passed between Servlets and JSPs within a single request. Use session attributes (req.getSession().setAttribute) for user-specific data that persists across multiple requests, such as login state or shopping cart contents.

Frequently Asked Questions

Can I read the request body in doGet()?▼