Using HttpServletResponse: Methods, Examples, and Best Practices

HttpServletResponse is the object a servlet uses to send HTTP responses to the client. This article introduces the most frequently used methods such as addCookie , addHeader , addIntHeader , setStatus , setDateHeader , setHeader , and setIntHeader , and explains that addXXX adds a header while setXXX replaces an existing header.

Four practical examples are presented:

Case 1 – Disable browser caching using setHeader to set Expires , Cache-Control and a custom progam header.

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // Disable caching
    resp.setHeader("Expires", "-1");
    resp.setHeader("Cache-Control", "No-Cache");
    resp.setHeader("progam", "No-Cache");

    // Write response body
    resp.getOutputStream().write("haha".getBytes());
}

Case 2 – Automatic page refresh with two sub‑cases.

a) Refresh the current page every second:

// Define a counter
int count = 0;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // Refresh every 1 second
    resp.setIntHeader("Refresh", 1);
    count++;
    resp.getOutputStream().write((count + "").getBytes());
}

b) Redirect to another page after three seconds:

// Redirect after 3 seconds
resp.setHeader("Refresh", "3;url=/myDay06/NoCacheResponse");
resp.getOutputStream().write("刷新".getBytes());

Case 3 – File download (both non‑Chinese and Chinese filenames).

a) Non‑Chinese filename download:

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext context = getServletContext();
    String path = context.getRealPath("/1.jpg");
    resp.setHeader("Content-Disposition", "attachment;filename=1.jpg");
    resp.setHeader("Content-type", "application/octet-stream");
    BufferedInputStream bis = new BufferedInputStream(new FileInputStream(path));
    BufferedOutputStream out = new BufferedOutputStream(resp.getOutputStream());
    byte[] buff = new byte[1024];
    int len = 0;
    while ((len = bis.read(buff)) != -1) {
        out.write(buff, 0, len);
        out.flush();
    }
    out.close();
    bis.close();
}

b) Chinese filename download (uses URLEncoder ):

public class FileChineseDownload extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = getServletContext();
        String path = context.getRealPath("/美女.jpg");
        String filename = path.substring(path.lastIndexOf("\\") + 1);
        resp.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode(filename, "utf-8"));
        resp.setHeader("Content-Type", "application/octet-Stream");
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(path));
        BufferedOutputStream out = new BufferedOutputStream(resp.getOutputStream());
        byte[] buff = new byte[1024];
        int len = 0;
        while ((len = bis.read(buff)) != -1) {
            out.write(buff, 0, len);
            out.flush();
        }
        bis.close();
        out.close();
    }
}

Case 4 – Dynamic verification image generation using BufferedImage , Graphics , and ImageIO to draw a captcha.

public class ActionImage extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int width = 200;
        int height = 50;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics gra = image.getGraphics();
        // Draw blue rectangle
        gra.setColor(Color.BLUE);
        gra.drawRect(0, 0, width, height);
        // Fill yellow background
        gra.setColor(Color.YELLOW);
        gra.fillRect(0, 0, width - 1, height - 1);
        // Draw interference lines
        Random rLine = new Random();
        gra.setColor(Color.BLACK);
        for (int x = 0; x < 10; x++) {
            gra.drawLine(rLine.nextInt(width), rLine.nextInt(height), rLine.nextInt(width), rLine.nextInt(height));
        }
        // Draw random digits in red, bold italic font
        gra.setColor(Color.RED);
        gra.setFont(new Font("宋体", Font.BOLD | Font.ITALIC, 23));
        Random rNumber = new Random();
        int x = 23;
        for (int i = 0; i < 4; i++) {
            gra.drawString(rNumber.nextInt(10) + "", x, 30);
            x += 40;
        }
        // Output image as JPEG
        ImageIO.write(image, "jpg", resp.getOutputStream());
    }
}

Important notes: a servlet must not mix character and byte streams; data written via streams is first stored in the response buffer and then sent according to the HTTP protocol; the container automatically closes streams after the response is committed.