上代码
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>生成验证码</title>
</head>
<body>
<hr color="blue"></hr>
请输入账号：<input name="userid" maxlength="20"/><br/>
请输入密码：<input name="password" type="password" maxlength="20"/><br/>
<form action="" method="post" name="formName">
请选择角色：<input type="radio" name="role" value="teacher" checked="checked">教师
<input type="radio" name="role" value="student">学生
</form>
请输入账号：<input name="userid" maxlength="20"/>
验证码：
<% //'A~Z' 65-90
//'0~9' 48-57
char[] c = {'0','1','2','3','4','5','6','7','8','9','Q','W','E','R','T','Y','U','I','O','P','A','S','D','F','G','H','J','K','L','Z','X','C','V','B','N','M'};
int n;
for(int i=0;i<4;i++){
n = (int)(Math.random()*36);
%>
<%=c[n] %>
<%
}
%>
<br/>
<button name="reset" value="重置">重置</button>
<button name="submit" valur="登录">登录</button>
<hr color="blue"></hr>
</body>
</html>效果如图