EL表达式的小结与简单例子

来源：互联网发布：马克思经济知乎编辑：程序博客网时间：2024/05/30 22:51

1、 EL表达式

1） [] .

2）算数操作符

3）关系运算符

4） Empty x

5）三目运算

6）隐含对象

pageContext

pageScope

requestScope

sessionScope

applicationScope

param

paramValues

header[“User-Agent”]

headerValues Map

initParam

getInitParameter

例子：

package action;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ELServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);

}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//传递引用
String a="abc";
String b="bcdk";
String c="ccddk";
request.getSession().setAttribute("obj1", b);
request.setAttribute("obj", a);
//传递list
ArrayList list=new ArrayList();
list.add(1);
list.add(2);
list.add(3);
request.setAttribute("list", list);
//传递map
Map m=new HashMap<String, String>();
m.put("s", "ssss");
m.put("n", "nnnn");
request.setAttribute("m", m);
//Empty
String t1="";
String t2=null;
String t3="asdd";
Integer t4=0;
request.setAttribute("t1", t1);
request.setAttribute("t2", t2);
request.setAttribute("t3", t3);
request.setAttribute("t4", t4);

request.getRequestDispatcher("EL.jsp").forward(request, response);
}

}

Jsp:

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>EL表达式</title>
</head>
<body>
会全部找--- all:${obj} 
只在request的范围里面找---request:${requestScope.obj} 
只会在session的范围里面找----session:${sessionScope.obj1} 
list传递
list:${list} 
listItem:${list[0]} 
把值打印出来:
<c:forEach items="${list}" var="list">
${list}
</c:forEach>
map打印值
map:${m}
mapitem1:${m.s}
mapitem2:${m['s'] } 
算数运算:
${1+2}
关系运算:
<c:if test="${list[0]>=1}">
${7+8}
</c:if>
Empty
t1isEmpty:${empty t1}
t2isEmpty:${empty t2}
t3isEmpty:${empty t3}
t4isEmpty:${empty t4}
param
======${param.name}
====${paramValues.check}

</body>
</html>

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