我的验证码小记

     所谓的验证码就是将一串随机产生的数字或符号，生成一幅图片， 图片里加上一些干扰象素（防止OCR），由用户肉眼识别其中的验证码信息，输入表单提交网站验证，验证成功后才能使用某项功能。

     验证码一般是防止有人利用机器人自动批量注册、对特定的注册用户用特定程序暴力破解方式进行不断的登陆、灌水。因为验证码是一个混合了数字或符号的图片，人眼看起来都费劲，机器识别起来就更困难。 一般注册用户ID的地方以及各大论坛都要要输入验证码。

     下面是我使用过的一个验证码的例子：

1.VerifyCodeServlet.java

public class VerifyCodeServlet extends HttpServlet        

{        

        private static final String CONTENT_TYPE = "text/html; charset=gb2312";        

        //设置字母的大小,大小        

        private Font mFont = new Font("Times New Roman", Font.PLAIN, 17);        

        public void init() throws ServletException        

        {        

                super.init();        

        }        

        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);        

        public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException        

                response.setHeader("Pragma","No-cache");        

                response.setHeader("Cache-Control","no-cache");        

                response.setDateHeader("Expires", 0);        

                //表明生成的响应是图片        

                response.setContentType("image/jpeg");        

                int width=100, height=18;        

                BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);        

                Graphics g = image.getGraphics();        

                g.setColor(getRandColor(200,250));        

                g.fillRect(1, 1, width-1, height-1);        

                g.setColor(new Color(102,102,102));        

                g.drawRect(0, 0, width-1, height-1);        

                g.setFont(mFont);        

                g.setColor(getRandColor(160,200));        

                //画随机线        

                for (int i=0;i<155;i++)        

                {        

                        int x = random.nextInt(width - 1);        

                        int y = random.nextInt(height - 1);        

                        int xl = random.nextInt(6) + 1;        

                        int yl = random.nextInt(12) + 1;        

                        g.drawLine(x,y,x + xl,y + yl);        

                }        

                //从另一方向画随机线        

                for (int i = 0;i < 70;i++)        

                        int xl = random.nextInt(12) + 1;        

                        int yl = random.nextInt(6) + 1;        

                        g.drawLine(x,y,x - xl,y - yl);        

                //生成随机数,并将随机数字转换为字母        

                String sRand="";        

                for (int i=0;i<6;i++)        

                        int itmp = random.nextInt(26) + 65;        

                        char ctmp = (char)itmp;        

                        sRand += String.valueOf(ctmp);        

                        g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));        

                        g.drawString(String.valueOf(ctmp),15*i+10,16);        

                HttpSession session = request.getSession(true);        

                session.setAttribute("rand",sRand);        

                g.dispose();        

                ImageIO.write(image, "JPEG", response.getOutputStream());        

        public void destroy()        

}    

2.web.xml

<servlet>     

        <servlet-name>verifyCodeServlet</servlet-name>     

        <servlet-class>com.yangfei.test.servlet.VerifyCodeServlet</servlet-class>     

</servlet>     

<servlet-mapping>     

<url-pattern>/verifyCodeServlet</url-pattern>     

</servlet-mapping>

3.页面：

<img src="verifyCodeServlet">

     本文转自NightWolves 51CTO博客，原文链接：http://blog.51cto.com/yangfei520/347460，如需转载请自行联系原作者