#code.jsp
<%@ page language="java"
import="java.util.*"
import="java.awt.*"
import="java.awt.image.BufferedImage"
import="javax.imageio.ImageIO"
pageEncoding="UTF-8"
%>
<%
response.setHeader("Cache-Control","no-cache");
int width = 60;
int height = 20;
int length = 4;
BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
//设置画笔
Graphics g = image.getGraphics();
//设定背景颜色
g.setColor(new Color(200,200,200));
g.fillRect(0, 0, width, height);
//取随机产生的验证码（四位数字）
String randStr = "";
Random random = new Random();
for (int i = 0; i < length; i++) {
boolean b = random.nextBoolean();
if (b) { // 字符串
int choice = random.nextBoolean() ? 65 : 97; //取得65大写字母还是97小写字母
randStr += (char) (choice + random.nextInt(26));// 取得大写字母
} else { // 数字
randStr += String.valueOf(random.nextInt(10));
}
}
session.setAttribute("randStr", randStr);
//将验证码显示到图像中
g.setColor(Color.black);
g.setFont(new Font("",Font.PLAIN,20));
g.drawString(randStr,5,17);
//随机产生100个干扰点，使图像不容易被其它程序探测
for(int i=0; i<100; i++){
int x = random.nextInt(width);
int y = random.nextInt(height);
g.drawOval(x,y,1,1);
}
//输出图像的到页面
ImageIO.write(image,"JPEG",response.getOutputStream());
out.clear();
out = pageContext.pushBody();
%>
# loginForm.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<html>
<body>
welcome
<br>
<form name="loginForm" method="post" action="/Pro27/servlet/CheckCode">
account:<input type="text" name="account"><br>
password:<input type="password" name="password"><br>
code:<input type="text" size="10" name="code">
<img name="imgValidate" src="code.jsp" onClick="refresh()">
<a href="javascript:refresh();">看不清,换一张 </a>
<br>
<input type="submit" value="login">
<br>
${sessionScope.codeCheck }
<%session.removeAttribute("codeCheck"); %>
</form>
</body>
<script type="text/javascript" language="JavaScript">
function refresh(){
loginForm.imgValidate.src = "code.jsp?"+Math.random();//new Date(); 此处必须加上Math.random()或new Date()，否则无法刷新验证码
}
</script>
</html>