在servlet中生成验证码

红太狼 2022-05-20 07:58 178阅读 0赞

## 验证码 ##

验证码的作用就是防止机器人的无限注册,导致本地数据库瞬间爆炸.今天学习servlet中生成验证码.

## 思路 ##

*  后台servlet专门生成验证码
 *  前台,img中src指向这个servlet的映射链接,从servlet中获取这个图片资源

## 代码 ##

后台代码:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            BufferedImage bfi = new BufferedImage(80, 25, BufferedImage.TYPE_INT_RGB);
            Graphics2D graphics = (Graphics2D) bfi.getGraphics();
    
            // 设置背景色
            graphics.setColor(Color.WHITE);
            graphics.fillRect(0, 0, 80, 25);
    
            // 设置边框
            graphics.setColor(Color.BLACK);
            graphics.drawRect(0, 0, 80-1, 25-1);
    
            String str = drawRandomNum(graphics);
            drawPoint(bfi);
            drawInfluencedLine(graphics);
    
            //禁用缓存
            response.setHeader("expries", "-1");
            response.setHeader("Cache-Control", "no-cache");
            response.setHeader("Pragma", "no-cache");
            response.setHeader("content-type","image/jpeg");
    
            // imageIO
            ImageIO.write(bfi, "jpg", response.getOutputStream());
        }
    
        // 画上点
        private void drawPoint(BufferedImage bfi) {
            int area = (int) (0.02 * 80 * 25);
            for (int i = 0; i < area; ++i) {
                int x = (int) (Math.random() * 80);
                int y = (int) (Math.random() * 25);
                bfi.setRGB(x, y, (int) (Math.random() * 255));
            }
        }
    
        private void drawInfluencedLine(Graphics2D g) {
            //设置验证码中的干扰线
            for (int i = 0; i < 3; i++) {
                Random random = new Random();
                //随机获取干扰线的起点和终点
                int xstart = random.nextInt(80);
                int ystart = random.nextInt(25);
                int xend = random.nextInt(80);
                int yend = random.nextInt(25);
                g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)));
                g.drawLine(xstart, ystart, xend, yend);
            }
        }
    
        // 生成随机数旋转后写入
        private String drawRandomNum(Graphics2D g) {
            char[] chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".toCharArray();
            Random random = new Random();
            int index;
            StringBuilder builder = new StringBuilder();
            for (int i = 0; i < 4; i++) {
                // 从字符数组中获得随机字符
                index = random.nextInt(chars.length);
                String value = chars[index] + "";
                // 设置随机字符的颜色
                g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)));
                // 字体格式
                Font font = new Font(null, Font.BOLD, 20);
                g.setFont(font);
                //生成-30~30之间的数字
                int dgree = random.nextInt(60) - 30;
                //旋转
                g.rotate(dgree * Math.PI / 180, i * 20 + 2, 23);
                // 写入字符
                g.drawString(value, i * 20 + 2, 20);
                // 把画笔再转回去,免得影响下次的弧度
                g.rotate(-dgree * Math.PI / 180, i * 20 + 2, 23);
                builder.append(value);
            }
            return builder.toString();
        }

前台代码:

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <body>
        <h2>这是1.html</h2>
        <img src="/jsp/ServletDemo1">
    </body>
    </html>

`效果图:`  
![这里写图片描述][70]

## 总结 ##

这种验证码的代码,最多也就用个这么一个位置,写好了,之后就可以复用了,用的不是那么多把.直接copy过去就行了.我自己模仿写着大概用了2个小时之久- -,拿去用吧~

缺少:

*  如何验证?
 *  如果前台生成验证码呢?比如js之类的,ajax?

[70]: /images/20220520/b26570774da640dba6e1803067327078.png