这个是图片生成的jsp：
<%@ page contentType="image/jpeg" import="java.awt.*,
java.awt.image.*,java.util.*,javax.imageio.*" pageEncoding="GB2312"%>
<%
// 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();
// 设定背景色
g.setColor(new Color(0xDCDCDC));
g.fillRect(0, 0, width, height);
//画边框
g.setColor(Color.black);
g.drawRect(0,0,width-1,height-1);
// 随机产生的认证码(4位数字)
String rand =""+ (Math.random()*10000);
rand = rand.substring(0,rand.indexOf("."));
System.out.println("rand:"+rand);
switch(rand.length())
{
case 1: rand = rand+"000"; break;
case 2: rand = rand+"00"; break;
case 3: rand = rand+"0"; break;
default: rand = rand.substring(0,4); break;
}
System.out.println("rand:"+rand);
// 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);
Integer tempNumber = new Integer(rand);
String numberStr = tempNumber.toString();
g.setFont(new Font("Atlantic Inline",Font.PLAIN,18));
String Str = numberStr.substring(0,1);
g.drawString(Str,8,17);
Str = numberStr.substring(1,2);
g.drawString(Str,20,15);
Str = numberStr.substring(2,3);
g.drawString(Str,35,18);
Str = numberStr.substring(3,4);
g.drawString(Str,45,15);
// 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 i=0;i<20;i++)
{
int x = random.nextInt(width);
int y = random.nextInt(height);
g.drawOval(x,y,0,0);
}
// 图象生效
g.dispose();
// 输出图象到页面
ImageIO.write(image, "JPEG",response.getOutputStream());
//在页面上调用 <img src="/yourPath/checkNum.jsp" />
out . clear();
out = pageContext.pushBody();
%>
做测试的部分代码：
<script type="text/javascript">
function refresh(){
document.myform.image.src = "code.jsp";
}
</script>
<body>
<img name="image" src="code.jsp" >
<a href="javascript:refresh()">看不清?换一张</a>
</body>
------解决方案--------------------------------------------------------
不懂……帮不了你
------解决方案--------------------------------------------------------
用的是IE浏览器吧，IE是有缓存的，火狐浏览器就没有这种问题
可以在URL链接后面加个动态的变量，验证码就会刷新了