jsp随机验证码图片生成

<%@ page contentType="image/jpeg" import="java.awt.*, java.awt.image.*,java.util.*,javax.imageio.*" %>
<%
        try {
            //在内存中创建图象
            int width = 60; //图像的宽度
            int height = 20; //图像的高度
              BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

            //获取图形上下文
            Graphics g = image.getGraphics();

            //设定背景色
            g.setColor(new Color(0xDCDCDC));
            g.fillRect(0, 0, width, height);

            //画边框
            g.setColor(Color.black);
            g.drawRect(0, 0, width - 1, height - 1);

            //取随机产生的认证码(4位数字)
            Random random = new Random();
            //生成0－9999的随机数
            int randomNum = random.nextInt(9999);
            //将验证码存在session中
            request.getSession().setAttribute("random",
                    String.valueOf(randomNum));
            String randStr = String.valueOf(randomNum);

            switch (randStr.length()) {
            case 1:
                randStr = "000" + randStr;
                break;
            case 2:
                randStr = "00" + randStr;
                break;
            case 3:
                randStr = "0" + randStr;
                break;
            default:
                randStr = randStr.substring(0, 4);
                break;
            }

            //将认证码显示到图象中
            g.setColor(Color.black);

            g.setFont(new Font("Atlantic Inline", Font.PLAIN, 18));
            String Str = randStr.substring(0, 1);
            g.drawString(Str, 8, 17);

            Str = randStr.substring(1, 2);
            g.drawString(Str, 20, 15);
            Str = randStr.substring(2, 3);
            g.drawString(Str, 35, 18);

            Str = randStr.substring(3, 4);
            g.drawString(Str, 45, 15);

            //          随机产生88个干扰点，使图象中的认证码不易被其它程序探测到
            for (int i = 0; i < 20; i++) {
                int x = random.nextInt(width);
                int y = random.nextInt(height);
                g.drawOval(x, y, random.nextInt(5), random.nextInt(5));
            }

            //          图象生效
            g.dispose();

            //          输出图象到页面
            ImageIO.write(image, "JPEG", response.getOutputStream());

        } catch (Exception e) {
            e.printStackTrace();
            out.println(e.toString());
        }
%>