我的驗證碼小記

     所謂的驗證碼就是将一串随機産生的數字或符号，生成一幅圖檔， 圖檔裡加上一些幹擾象素（防止OCR），由使用者肉眼識别其中的驗證碼資訊，輸入表單送出網站驗證，驗證成功後才能使用某項功能。

     驗證碼一般是防止有人利用機器人自動批量注冊、對特定的注冊使用者用特定程式暴力破解方式進行不斷的登陸、灌水。因為驗證碼是一個混合了數字或符号的圖檔，人眼看起來都費勁，機器識别起來就更困難。 一般注冊使用者ID的地方以及各大論壇都要要輸入驗證碼。

     下面是我使用過的一個驗證碼的例子：

1.VerifyCodeServlet.java

public class VerifyCodeServlet extends HttpServlet        

{        

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

        //設定字母的大小,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);        

                //表明生成的響應是圖檔        

                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));        

                //畫随機線        

                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);        

                }        

                //從另一方向畫随機線        

                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);        

                //生成随機數,并将随機數字轉換為字母        

                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.頁面：

<img src="verifyCodeServlet">

     本文轉自NightWolves 51CTO部落格，原文連結：http://blog.51cto.com/yangfei520/347460，如需轉載請自行聯系原作者