简单的验证码实现逻辑及点击切换

为了防止恶意表单注册，注册界面都会加上验证码功能。服务器会在内存生成验证码图片，并显示随机内容到网页，并且要防止智能识别。具体代码如下：

验证码图片生成

@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int width = 100;
        int height = 50;
        //创建一个对象，在内存中画图（验证码图片对象）
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_3BYTE_BGR);
        //美化图片
        //填充背景色
        Graphics g = image.getGraphics();//画笔对象
        g.setColor(Color.pink);//设置画笔颜色
        g.fillRect(0,0,width,height);
        //画边框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width -1,height-1);

        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        //生成随机脚标
        Random ran = new Random();

        //写验证码
        for (int i = 1; i <= 4; i++) {
            int index = ran.nextInt(str.length());
            //获取字符
            char ch = str.charAt(index);
            g.drawString(ch+"",width/5*i,height/2);
        }

        //画干扰线
        g.setColor(Color.green);
        //随机生成坐标点
        for (int i = 0; i < 10; i++) {
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);

            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }

        //键土拍你输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

图片点击切换

<body>
    <img id="checkCode" src="/day15/checkCodeServlet" onclick="this.src='/day15/checkCodeServlet?' + new Date().getTime();"/>
    <a id="change" href="">看不清换一张</a>
</body>

服务器会有图片缓存，路径不变的画服务器不会发送新数据到客户端，验证码就不能刷新，可以加随机数或时间戳到路径后。

验证码