用户管理系统（登录操作）
用户输入用户名密码后从数据库查询信息 比对用户名密码后允许登录
<%@ 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>Insert title here</title>
</head>
<body>
<%
Object message = request.getAttribute("message");
if(message!=null && !"".equals(message)){
%>
<script type="text/javascript">
alert("<%=request.getAttribute("message")%>");
</script>
<%if(message.equals("密码正确")){ %>
<%
request.getRequestDispatcher("user.jsp").forward(request,response);}%>
<%} %>
<div style="position:absolute;100%;height:100%;background:#7FDBFF;">
<div style="position:absolute;text-align:center;color:red;100%;height:20%;top:0;font-size:100px;">
用户登录
</div>
<div style="position:absolute;60%;height:40%;top:30%;left:20%;">
<form action="UserServlet?method=enter" method="post">
<table>
<tr>
<td>role:</td>
<td><input type="text" name="role" id="role"style="400px;height:30px"><br></td>
</tr>
<tr>
<td>id:</td>
<td><input type="text" name="UserID" id="UserID"style="400px;height:30px"><br></td>
</tr>
<tr>
<td>密码:</td>
<td><input type="password" name="Password" id="password"style="400px;height:30px"><br></td>
</tr>
<tr>
<td><button type="submit" onclick="return check()">登录</button></td>
<td><a href="userZ.jsp">注册</a></td>
</tr>
</table>
</form>
</div>
</div>
<script type="text/javascript">
function check() //封装一个<body>中做成点击事件的函数
{
if(document.getElementById('UserID').value==''||document.getElementById('role').value==''||document.getElementById('Password').value=='') {
alert('有为空信息！');
return false;
}else {return true;}
}
</script>
</body>
</html>