（JSP）EL——优化登录界面，获取对象，获取数据

EL优化登录界面

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'login.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
 	<form action="loginServlet" method="post">
 		姓名:<input type="text" name="username"><br>
 		密码:<input type="password" name="userpassword">
 	<button>登录</button> 
 	<span style="color: red;font-size:12px">${msg}</span>
 	</form>
  </body>
</html>

将<span style="color: red;font-size:12px"><%=request.getAttribute("msg") %></span>

改成<span style="color: red;font-size:12px">${msg}</span>

节省了代码量也提高了效率

效果如下：

在msg为NULL的时候，msg并不会显示。

EL获取对象

EL操作不了局部变量。

EL在操作域对象的时候一般是从小到大依次访问。

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'EL.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
    <%
    //设置page属性
    pageContext.setAttribute("name","zhangsan");
    
     //设置request属性
    request.setAttribute("name","lisi");
    
     //设置session属性
    session.setAttribute("name","wangwu");
    
     //设置appication属性
    application.setAttribute("name","zhaoliu");
    
    String str = "Hello ";
     %>
     //获取局部变量
     ${str}<br>
     //获取域对象
     ${name}<br>
  </body>
</html>