登陸頁面加入驗證碼，這個小栗子
用到了兩個頁面，0-9十個數字圖片（例如下面的8150）大家可以替換自己喜歡的圖片
1. index.jsp：
<%@ page language="java" import="java.util.*" pageEncoding="gbk"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>登錄頁面</title> <script type="text/javascript">
function loginCheck() {
if(loginForm.userName.value == "") {
alert("用戶名不能爲空，請輸入用戶名！");
loginForm.userName.focus();
return false;
}
if(loginForm.userPassword.value == "") {
alert("密碼不能爲空，請輸入密碼！");
loginForm.userPassword.focus();
return false;
}
if(loginForm.verification2.value == "") {
alert("驗證碼不能爲空，請輸入驗證碼！");
loginForm.verification2.focus();
return false;
}
if(loginForm.verification2.value != loginForm.verification1.value) {
alert("驗證碼錯誤！");
loginForm.verification2.focus();
return false;
}
return true;
}
</script>
</head>
<body>
<form name="loginForm" action="check.jsp" method="post" οnsubmit="return loginCheck();">
<table align="center">
<tr align="center">
<td colspan="2"><h1>歡迎登錄</h1></td>
</tr>
<tr>
<td>用戶名：</td>
<td><input name="userName" type="text"/></td>
</tr>
<tr>
<td>密 碼：</td>
<td><input name="userPassword" type="password"/></td>
</tr>
<%//獲取隨機數
int num1 = (int)(Math.random() * 10);
int num2 = (int)(Math.random() * 10);
int num3 = (int)(Math.random() * 10);
int num4 = (int)(Math.random() * 10);
String num = num1 + "" + num2 + num3 + num4;
%>
<span style="color:#339999;background-color: rgb(255, 255, 255);"> <!-- 寫一個隱藏域，用來進行驗證比較 --></span>
<tr>
<td><input name="verification1" type="hidden" value="<%=num %>"/></td>
</tr>
<tr>
<td>驗證碼：</td>
<td>
<input name="verification2" type="text" style="width: 60px;">
<img src="image/<%=num1 %>.png" />
<img src="image/<%=num2 %>.png" />
<img src="image/<%=num3 %>.png" />
<img src="image/<%=num4 %>.png" />
</td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="提交">
<input type="reset" value="重置">
</td>
</tr>
</table>
</form>
</body>
</html>
<%@ page language="java" import="java.util.*" pageEncoding="gbk"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>檢查頁面</title>
</head>
<body>
<%
String name = request.getParameter("userName");
String password = request.getParameter("userPassword");
String message;
if(name.equals("li") && password.equals("123456")) {
message = "可以登錄系統！";
} else {
message = "用戶名或密碼錯誤！";
}
%>
<script type="text/javascript">
alert("<%=message%>");
window.location.href = 'login.jsp';
</script>
</body>
</html>