验证码的生成

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public static void ImageCodeMaker(){             // 定义图片的宽度和高度             int width = 90, height = 40;             // 创建一个图像对象             BufferedImage image = new BufferedImage(width, height,                     BufferedImage.TYPE_INT_RGB);             // 得到图像的环境对象             Graphics g = image.createGraphics();                           g.setColor(getRandColor(180, 250));              g.fillRect(0, 0, width, height);                            Random random = new Random();                           for (int i = 0; i < 5; i++) {                 g.setColor(getRandColor(50, 100));                 int x = random.nextInt(width);                 int y = random.nextInt(height);                 g.drawOval(x, y, 4, 4);             }             // 设置字体，下面准备画随机数             g.setFont(new Font("", Font.PLAIN, 40));             // 随机数字符串             String sRand = "";             for (int i = 0; i < 4; i++) {                 // 生成四个数字字符                 String rand = getRandomChar();;                         //String.valueOf(random.nextInt(10));                 sRand += rand;                 // 生成随机颜色                 g.setColor(new Color(20 + random.nextInt(80), 20 + random                         .nextInt(100), 20 + random.nextInt(90)));                 // 将随机数字画在图像上                 g.drawString(rand, (17 + random.nextInt(3)) * i + 8, 34);                       // 生成干扰线                     for (int k = 0; k < 12; k++) {                         int x = random.nextInt(width);                         int y = random.nextInt(height);                         int xl = random.nextInt(9);                         int yl = random.nextInt(9);                         g.drawLine(x, y, x + xl, y + yl);                     }             }             System.out.println(sRand);                   }       private static String getRandomChar() {           String ret ="";                   //数字和字母的组合          String baseNumLetter = "0123456789ABCDEFGHJKLMNOPQRSTUVWXYZ";         //纯数字         // String baseNum = "0123456789";          //纯字母         // String baseLetter = "ABCDEFGHJKLMNOPQRSTUVWXYZ";                    // ret = baseLetter.charAt(new Random().nextInt(baseLetter.length()))+"";                    // ret = baseNum.charAt(new Random().nextInt(baseNum.length()))+"";                     ret = baseNumLetter.charAt(new Random().nextInt(baseNumLetter.length()))+"";                                           return ret;     }                 /**              * 产生一个随机的颜色              *              * @param fc              *            颜色分量最小值              * @param bc              *            颜色分量最大值              * @return              */             public static Color getRandColor(int fc, int bc) {                 Random random = new Random();                 if (fc > 255){                     fc = 255;                 }                 if (bc > 255){                     bc = 255;                 }                 int r = fc + random.nextInt(bc - fc);                 int g = fc + random.nextInt(bc - fc);                 int b = fc + random.nextInt(bc - fc);                 return new Color(r, g, b);             }

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在页面显示时 需要如下代码：
// 首先设置页面不缓存  
        response.setHeader("Pragma", "No-cache");  
        response.setHeader("Cache-Control", "no-cache");  
        response.setDateHeader("Expires", 0);  


 // 将生成的随机数字字符串写入Session  
        request.getSession(false).setAttribute("randcode", sRand);  
        // 使图像生效  
        g.dispose();  
        // 输出图像到页面  
        ImageIO.write(image, "JPEG", response.getOutputStream());