图书管理系统登录界面（模板）：
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%> <!DOCTYPE html> <html> <head> <title>Login!</title> <script type="text/javascript"> function checkaccount() { var x=document.getElementById("account").value; if(x.length>20) { alert("用户账户位数不能大于20") document.getElementById("account").value = ""; } } function checkpwd() { var x=document.getElementById("password").value; if(x.length>20) { alert("密码最大只有20位") document.getElementById("password").value = ""; } } function Checka(){ var Username = document.getElementById("account").value; if (Username == "" || account.value == null ) { alert("用户名不能为空"); } } function Checkp(){ var Username = document.getElementById("password").value; if (Username == "" || password.value == null ) { alert("密码不能为空"); } } </script> </head> <body style="text-align:center;"> <br><br><br> <form name="form2" action="Login" method="post"> 帐号 <input type="text" name="account" id="account" onblur="Checka();checkaccount();"><br><br> 密码 <input type="password" name="password" id="password" onblur="Checkp;checkpwd();"><br><br> <input type="submit" value="登录"> </form> </body> </html>