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();        
                Random random = new Random();        
                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 x = random.nextInt(width - 1);        
                         int y = random.nextInt(height - 1);        
                         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 >    
         < servlet-name >verifyCodeServlet </ servlet-name >    
< url-pattern >/verifyCodeServlet </ url-pattern >    
</ servlet-mapping >

 

3.页面：

< img src =" verifyCodeServlet">