el表达式

//普通字符串
		request.setAttribute("hello", "hello World");
		
		//结构
		Group group=new Group();
		group.setId(1);
		group.setName("尚学堂");
		
		User user=new User();
		user.setName("谷超");
		user.setAge(27);
		user.setGroup(group);
		
		request.setAttribute("user", user);
		
		//map
		Map map=new HashMap();
		map.put("key1", "value1");
		map.put("key2", "value2");
		
		request.setAttribute("map", map);
		
		//数组
		String[] strArr=new String[]{"hello","world","ni","hao"};
		request.setAttribute("strArr", strArr);
		
//		对象数组
		User[] users=new User[10];
		for(int i=0;i<10;i++){
			User u=new User();
			u.setName("User"+i);
			users[i]=u;
		}
		request.setAttribute("users", users);
		
//		list
		ArrayList list=new ArrayList();
		for(int i=0;i<10;i++){
			User u=new User();
			u.setName("User"+i);
			list.add(u);
		}
		request.setAttribute("userList", list);
		
		//empty
		request.setAttribute("value1", null);
		request.setAttribute("value2", "");
		request.setAttribute("value3", new ArrayList());
		request.setAttribute("value4", "11111");

JSP中代码

<li>普通字符串</li><br>
hello(jsp 脚本)：<%=request.getAttribute("hello") %><br>
hello(el表达式)：${hello }<br>
el表达式，el的隐含对象pageScope，requestScope,sessionScope,applicationScope<br>
hello(el表达式)：${requestScope.hello }<br>
hello(el表达式，从sessionScope中取得)：${sessionScope.hello }<br>

<li>结构</li><br>
姓名：${user.name }<br>
年龄：${user.age }<br>
所属组：${user.group.name}<br>

<li>map</li><br>
mapvalue.key1:${map.key1 }<br>
mapvalue.key2:${map.key2 }<br>

<li>数组，采用[]和下标</li><br>
strArr[2]:${strArr[2] }<br>

<li>对象数组，采用[]和下标</li><br>
userArr[2].name:${users[2].name }<br>

<li>list</li><br>
userList[5].name:${userList[5].name }<br> 

<li>el表达式对运算符的支持</li><br>
1+2=${1+2 }<br>
10/5=${10/5 }<br>
10 div 5=${10 div 5 }<br>
10 % 3=${10 % 3 }<br>
10 mod 3=${10 mod 3 }<br>
4 > 3=${4> 3 }<br>
<!-- 
	==/eg
	!=/ne
	</lt
	>/gt
	<=/le
	>=/ge
	&&/and
	||/or
	!/not
	/ / div
	%/mod

        +

        -

        *  
 -->
 
<li>测试empty</li><br>
value1:${empty value1 }<br>
value2:${empty value2 }<br>
value3:${empty value3 }<br>
value4:${empty value4 }<br>

通常和jstl结合使用，表达式语言有三个重要部分

EL隐式对象 pageScope，requestScope,sessionScope,applicationScope

存取器

运算符

using functions <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn"%> ${fn:contains(var1,'hello')}