- 以下代码随机产生四位数字的验证码：
- 1）生成验证码的jsp代码：
<%@ page language="java" import="java.awt.*" contentType="image/jpeg"
import="java.awt.image.BufferedImage" import="java.util.*"
import="javax.imageio.*" pageEncoding="UTF-8"%>
<%
response.setHeader("Cache-Control", "no-cache");
// 在内存中创建图象
int width = 60, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
//获取画笔
Graphics g = image.getGraphics();
//设定背景色
g.setColor(new Color(200, 200, 200));
g.fillRect(0, 0, width, height);
//取随机产生的验证码(4位数字)
Random rnd = new Random();
int randNum = rnd.nextInt(8999) + 1000;
String randStr = String.valueOf(randNum);
//将验证码存入session
session.setAttribute("randStr", randStr);
//将验证码显示到图象中
g.setColor(Color.black);
g.setFont(new Font("", Font.PLAIN, 20));
g.drawString(randStr, 10, 17);
// 随机产生100个干扰点，使图象中的验证码不易被其他程序探测到
for (int i = 0; i < 100; i++) {
int x = rnd.nextInt(width);
int y = rnd.nextInt(height);
g.drawOval(x, y, 1, 1);
}
// 输出图象到页面
ImageIO.write(image, "JPEG",response.getOutputStream());
out.clear();
out = pageContext.pushBody();
%>
登录界面显示验证码，点击 看不清，换一个 更换验证码
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>登录</title>
</head>
<body>
<script language="javascript" type="text/javascript">
function refresh(imgUrl){
var getImgCode=document.getElementById("codeImg");
getImgCode.src=imgUrl+"?id="+Math.random();
}
</script>
欢迎登陆本系统！<br>
<form name="loginForm" action="login.jsp" method="post">
账号：<input type="text" name="account"/><br>
密码：<input type="password" name="password" /><br>
验证码：<input type="text" name="code" size="10" >
<img id="codeImg" name="codeImg" alt="验证码" src="validate.jsp" >
<a href="javascript:refresh('validate.jsp')">看不清，换一个</a><br>
<input type="submit" value="登录" >
</form>
</body>
</html>效果图: