用JSP实现的验证码

image.jsp

<%@ page contentType="image/jpeg"%>
<%@ page import="java.awt.*"%>
<%@ page import="java.awt.image.*"%>
<%@ page import="java.util.*"%>
<%@ page import="javax.imageio.*"%>
<%
//在内存中创建图象
int iWidth=130,iHeight=18;
BufferedImage image=new BufferedImage(iWidth,iHeight,BufferedImage.TYPE_INT_RGB);
//获取图形上下文
Graphics g=image.getGraphics();
//设定背景色
g.setColor(Color.white);
g.fillRect(0,0,iWidth,iHeight);
//画边框
g.setColor(Color.black);
g.drawRect(0,0,iWidth-1,iHeight-1);
//取随机产生的认证码(4位数字)
String rand=request.getParameter("Rand");
rand=rand.substring(0,rand.indexOf("."));
switch(rand.length())
{
case 1:rand="000"+rand;break;
case 2:rand="00"+rand;break;
case 3:rand="0"+rand;break;
default:rand=rand.substring(0,4);break;
}
//将认证码存入SESSION
session.setAttribute("Rand",rand);
//将认证码显示到图象中
g.setColor(Color.black);
g.setFont(new Font("Times New Roman",Font.PLAIN,18));
g.drawString(rand,10,15);
//随机产生88个干扰点,使图象中的认证码不易被其它程序探测到
Random random=new Random();
for(int iIndex=0;iIndex<88;iIndex++)
{
int x=random.nextInt(iWidth);
int y=random.nextInt(iHeight);
g.drawLine(x,y,x,y);
}
//图象生效
g.dispose();
//输出图象到页面
ImageIO.write(image,"JPEG",response.getOutputStream());
%>

输出时应用验证码

<script>document.write("<img border=0 src='/image.jsp?Rand="+Math.random()*10000+"'>");</script><br>
  输认证码: <input name="Rand" maxlength=4 size="10"><br>

登录认证:

String Rand=request.getParameter("Rand");
String strRand=(String)session.getAttribute("Rand");
if(!strRand.equals(Rand))