EL基础教程

EL基础教程

El标签语法

${参数名}

EL标签的功能

1. 可以访问JSP中不同的域的对象
2. 可以访问JavaBean中的属性
3. 可以访问集合元素
4. 支持简单的运算操作

访问JSP中不同的域的对象

<%
 pageContext.setAttribute("name1", "zhangsan");
 request.setAttribute("name2", "lisi");
 session.setAttribute("name3", "wangwu");
 application.setAttribute("name4", "liuliu");
 %>

${pageScope.name1 } ${requestScope.name2 } ${sessionScope.name3 }
${applicationScope.name4 }



${name1 } ${name2 } ${name3 } ${name4 }

访问JavaBean中的属性

<%
	User user=new User("zhangsan",20,"北京");
	request.setAttribute("user", user);
%>
user name:${user.name }
 
user age:${user.age }
 
user address:${user.address }

访问集合元素

<%
	//数组
	int[] array=new int[]{1,2,3};
	//列表
	List list=new ArrayList();
	list.add("list1");
	list.add(20);
	list.add(true);
	pageContext.setAttribute("array", array);
	pageContext.setAttribute("list", list);
%>
数组:${array[0] },${array[1] },${array[2] }
 
List列表:${list }

简单的运算操作

算术运算符:

2+3=${2+3 }
2-3=${2-3 }
2*3=${2*3 }
2/3=${2/3 }

逻辑运算符:

true&&false=${true&&false }	
true||false=${true||false }	
!true=${!true }	

关系运算符:

2==5 ${2==5 }
2!=5 ${2!=5 }
2>5 ${2>5 }
2<5 ${2<5 }
2>=5 ${2>=5 }
2<=5 ${2<=5 }

其他运算符:

<%
	User user=new User();
	User user1=new User("zhangsan",20,"北京");
	String arr=new String();
	String[] arr1=new String[]{"one","two"};		
	
	pageContext.setAttribute("user", user);
	pageContext.setAttribute("user1", user1);
	pageContext.setAttribute("arr", arr);		
	pageContext.setAttribute("arr1", arr1);
%>
user 是否为空:${empty user }
arr 是否为空:${empty arr }
user1 是否为空:${empty user1 }
arr1 是否为空:${empty arr1 }
三元目运算符2<5?yes:no:${2<5?"yes":"no" }
user1.address:${user1.address }
arr1[1]:${arr1[1] }

EL标签的隐形变量

1. page <==============================> pageScope
2. request <============================> requestScope
3. session <============================> sessionScope
4. application <=========================> applicationScope
5. request.getParameter(String name) <=======> param

A.jsp

B.jsp

${param.name }

6. request.getParameterValues(String name) <==> paramValues

A.jsp

B.jsp

${paramValues.name[0] },${paramValues.name[1] }

7. request.getHeader(String name) <=========> header
8. request.getHeaderNames() <=============> headerValues
9. 所有请求cookie <=====================> cookie
10. application.getInitParameter(String name) <==> initParam
11. pageContext

${pageContext.request.queryString}
${pageContext.request.requestURL}
${pageContext.request.contextPath }
${pageContext.request.method }
${pageContext.request.protocol }
${pageContext.request.remoteUser }
${pageContext.request.remoteAddr }
${pageContext.session.id }
${pageContext.servletContext.serverInfo }