java生成验证码jsp

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class CaptchaServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int width = 100;
        int height = 30;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        g.setColor(new Color(255, 255, 255));
        g.fillRect(0, 0, width, height);
        g.setFont(new Font("Arial", Font.BOLD, 20));

        Random random = new Random();
        String captcha = "";
        for (int i = 0; i < 5; i++) {
            String rand = String.valueOf(random.nextInt(10));
            captcha += rand;
            g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));
            g.drawString(rand, 15 * i + 6, 20);
        }

        HttpSession session = request.getSession();
        session.setAttribute("captcha", captcha);

        response.setContentType("image/jpeg");
        ImageIO.write(image, "jpeg", response.getOutputStream());
        g.dispose();
    }
}

<img src="CaptchaServlet" alt="验证码" onclick="this.src='CaptchaServlet?'+Math.random();"/>