我现在做的一个网站登陆页面 验证码 是随机数，在验证码产生的页面设置为：
//设置页面不缓存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);我做的网站www.v-v-v.cn但是发现问题，当打开首页，先不登陆，而是点击首页其它连接，然受再在首页登陆，就会提示验证码错误，请问各位怎莫解决这个问题
//设置页面不缓存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);我做的网站www.v-v-v.cn但是发现问题，当打开首页，先不登陆，而是点击首页其它连接，然受再在首页登陆，就会提示验证码错误，请问各位怎莫解决这个问题
import java.awt.image.*;
import java.util.*;/**
* @author
*
* To change the template for this generated type comment go to
* Window>Preferences>Java>Code Generation>Code and Comments
*/
public class Image {public String sRand="";public Color getRandColor(int fc,int bc){//给定范围获得随机颜色
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 BufferedImage creatImage(){// 在内存中创建图象
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 获取图形上下文
Graphics g = image.getGraphics();//生成随机类
Random random = new Random();// 设定背景色
g.setColor(getRandColor(200,250));
g.fillRect(0, 0, width, height);//设定字体
g.setFont(new Font("Times New Roman",Font.PLAIN,18));//画边框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);
// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
g.setColor(getRandColor(160,200));
for (int i=0;i<155;i++)
{
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(12);
int yl = random.nextInt(12);
g.drawLine(x,y,x+xl,y+yl);
}// 取随机产生的认证码(4位数字)
//String rand = request.getParameter("rand");
//rand = rand.substring(0,rand.indexOf("."));for (int i=0;i<4;i++){
String rand=String.valueOf(random.nextInt(10));
sRand+=rand;
// 将认证码显示到图象中
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
g.drawString(rand,13*i+6,16);
}
// 图象生效
g.dispose();
return image;
}
}
页面
<%@ page contentType="image/jpeg" import="javax.imageio.*" %>
<html>
<head>
<title>验证码</title>
</head>
<body leftmargin="0" topmargin="0">
<jsp:useBean id="image" scope="session" class="com.my.test.computer.Image"/>
<%
//设置页面不缓存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);
// 将认证码存入SESSION
session.setAttribute("rand",image.sRand);
//String rand1=image.sRand.toString();
//String rand1=(String) session.getAttribute("rand");
// 输出图象到页面
ImageIO.write(image.creatImage(), "JPEG", response.getOutputStream());
%>
<table width="96%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td><%=image.sRand%></td>
</tr>
</table>
</body>
</html>