java里的验证码

 最近在一个J2EE系统里，要用到验证码，找到如下比较好的方法，是写成servlet的

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.awt.*;
import java.awt.image.*;
import java.util.*;
import javax.imageio.*;

/**
 * @author  yeeku.H.lee [email protected]
 * @version  1.0
 * <br>Copyright (C), 2005-2008, yeeku.H.Lee
 * <br>This program is protected by copyright laws.
 * <br>Program Name:
 * <br>Date:
 */
public class AuthImg extends HttpServlet
{
    private Font mFont = new Font("Arial Black", Font.PLAIN, 16);
    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);
        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));
        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);
        }
        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);
        }

        String sRand="";
        for (int i=0;i<6;i++)
        {
   String tmp = getRandomChar();
            sRand += tmp;
            g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
         g.drawString(tmp,15*i+10,15);
        }

        HttpSession session = request.getSession(true);
        session.setAttribute("rand",sRand);
        g.dispose();
        ImageIO.write(image, "JPEG", response.getOutputStream());
    }
    private String getRandomChar()
    {
  int rand = (int)Math.round(Math.random() * 2);
  long itmp = 0;
  char ctmp = '\u0000';
  switch (rand)
  {
   case 1:
    itmp = Math.round(Math.random() * 25 + 65);
    ctmp = (char)itmp;
    return String.valueOf(ctmp);
   case 2:
    itmp = Math.round(Math.random() * 25 + 97);
    ctmp = (char)itmp;
    return String.valueOf(ctmp);
   default :
    itmp = Math.round(Math.random() * 9);
    return String.valueOf(itmp);
  }
    }
}
 其中这是加了干扰线的了，并且用session来保存验证码了，
在登陆的jsp页面中，应该这样设置
 验证码如图：<img src="authImg" id="authImg"/>看不清？<a href="#" onClick="refresh()">单击此处刷新</a>
然后refesh()函数如下写
<script>
   function refresh()
   {
    document.getElementById("authImg").src='authImg?now=' + new Date();
   }
  </script>
之所以在最后加now,是防止浏览器的缓存

最后再在web.xml里配置下servlet

 <servlet>
        <servlet-name>img</servlet-name>
        <servlet-class>org.yeeku.web.AuthImg</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>img</servlet-name>
     <url-pattern>/authImg</url-pattern>
    </servlet-mapping>