实例解析JSP中EL表达式的各种运用
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2023-11-07 12:45:40
el运算符：
<%@page language="java" contenttype="text/html;charset=gb2312"%>...
el运算符：
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<%@page import="java.sql.*" %>
<!doctype html>
<html>
<head>
<title>el算数运算符</title>
</head>
<body>
<table border=1>
<tr>
<td>算数运算符</td>
<td>结果</td>
</tr>
<tr>
<td>加法运算符\${1 + 1}</td>
<td>结果${1+1}</td>
</tr>
<tr>
<td>减法运算符\${1 - 1}</td>
<td>结果${1-1}</td>
</tr>
<tr>
<td>乘法运算符\${1 * 2}</td>
<td>结果${1 * 1}</td>
</tr>
<tr>
<td>除法运算符\${3 / 2}</td>
<td>结果${3 / 2}</td>
</tr>
<tr>
<td>求余运算符\${3 % 2}</td>
<td>结果${3 % 2}</td>
</tr>
</table>
<table border=1>
<tr>
<td>关系运算符</td>
<td>结果</td>
</tr>
<tr>
<td>等于运算符\${1 == 1}</td>
<td>结果${1==1}</td>
</tr>
<tr>
<td>不等于运算符\${1 != 1}</td>
<td>结果${1!=1}</td>
</tr>
<tr>
<td>小于运算符\${1 < 2}</td>
<td>结果${1 < 2}</td>
</tr>
<tr>
<td>大于运算符\${3 > 2}</td>
<td>结果${3 > 2}</td>
</tr>
<tr>
<td>小于等于运算符\${1 <= 2}</td>
<td>结果${1 <= 2}</td>
</tr>
<tr>
<td>大于等于运算符\${3 >= 2}</td>
<td>结果${3 >= 2}</td>
</tr>
</table>
<table border=1>
<tr>
<td>逻辑运算符</td>
<td>结果</td>
</tr>
<tr>
<td colspan="2">逻辑运算符&&</td>
</tr>
<tr>
<td>\${true && true}</td>
<td>结果${true && true}</td>
</tr>
<tr>
<td>\${true && false}</td>
<td>结果${true && false}</td>
</tr>
<tr>
<td>\${false && false}</td>
<td>结果${false && false}</td>
</tr>
<tr>
<td colspan="2">逻辑运算符||</td>
</tr>
<tr>
<td>\${true || true}</td>
<td>结果${true || true}</td>
</tr><tr>
<td>\${true || false}</td>
<td>结果${true || false}</td>
</tr><tr>
<td>\${false || false}</td>
<td>结果${false || false}</td>
</tr>
<tr>
<td colspan="2">逻辑运算符!</td>
</tr>
<tr>
<td>\${!true}</td>
<td>结果${!true}</td>
</tr><tr>
<td>\${!false}</td>
<td>结果${!false}</td>
</tr>
</table>
<table border=1>
<tr>
<td>条件运算符</td>
<td>结果</td>
</tr>
<tr>
<td>\${2>1?"yes":"no"}</td>
<td>结果${2>1?"yes":"no"}</td>
</tr>
<tr>
<td>\${2<1?"yes":"no"}</td>
<td>结果${2<1?"yes":"no"}</td>
</tr>
</table>
<table border=1>
<tr>
<td>验证运算符</td>
<td>结果</td>
</tr>
<tr>
<td>\${empty param.username}</td>
<td>结果${empty param.username}</td>
</tr>
<tr>
<td>\${empty param.password}</td>
<td>结果${empty param.password}</td>
</tr>
</table>
<table border=1>
<tr>
<td>括号运算符及运算符的优先级</td>
<td>结果</td>
</tr>
</table>
</body>
</html>
el处理内置对象：
“.”和"[]"符号是用来存取数据的
${applicationscope.user.username}
${applicationscope.user[0].username}
${applicationscope.user["user-name"]}
通过变量来传值就必须使用[]
${applicationscope.user["data"]}
与存储有关的内置对象
<!doctype html>
<html>
<head>
<title>与存储有关的内置对象</title>
</head>
<body>
<%
//application范围设置属性name，值为application_name
application.setattribute("name","application_name");
//session范围设置属性name，值为session_name
session.setattribute("name","session_name");
//request范围设置属性name，值为request_name
request.setattribute("name","request_name");
//page范围设置属性name，值为page_name
pagecontext.setattribute("name","page_name");
%>
<%--获取page范围内的name属性--%>
page范围内的那么属性的值为：${pagescope.name}<br />
<%--获取request范围内的name的属性--%>
request范围内的那么属性的值为：${requestscope.name}<br />
<%--获取session范围内的name的属性--%>
session范围内的那么属性的值为：${sessionscope.name}<br />
<%--获取application范围内的name属性--%>
application范围内的那么属性的值为：${applicationscope.name}<br />
</body>
</html>
与输入有关的内置对象
<!doctype html>
<html>
<head>
<title>用户表单</title>
</head>
<body>
<form action="userdemo.jsp" method="post">
用户名：<input type="text" name="username" /><br />
密码：<input type="password" name="password" /><br />
姓名：<input type="text" name="name" /><br />
性别：<input type="radio" name="sex" value="男">男<input type="radio" name="sex" value="女">女<br />
爱好：<br />
<input type="checkbox" name="interest" value="打篮球">打篮球<br />
<input type="checkbox" name="interest" value="看书">看书<br />
<input type="checkbox" name="interest" value="旅行">旅行<br />
<input type="checkbox" name="interest" value="编程">编程<br />
<input type="submit" value="提交">
<input type="reset" value="重置">
</form>
</body>
</html>
<!doctype html>
<html>
<head>
<title>接收用户参数</title>
</head>
<body>
<%
//设置页面编码格式
request.setcharacterencoding("gb2312");
%>
<%--接收用户参数--%>
用户名：${<span style="color:#003399;">param</span>.username}<br />
密码：${<span style="color:#003399;">param</span>.password}<br />
姓名：${<span style="color:#003399;">param</span>.name}<br />
性别：${<span style="color:#003399;">param</span>.sex}<br />
爱好：${<span style="color:#003399;">paramvalues</span>.interest[0]}
${<span style="color:#003399;">paramvalues</span>.interest[1]}
</body>
</html>
cookie内置对象
<!doctype html>
<html>
<head>
<title>设置cookie的值</title>
</head>
<body>
<%
//设置cookie的值
cookie c = new cookie("username","root");
//添加cookie到客户端
response.addcookie(c);
%>
<a href="getcookiedemo.jsp">显示cookie的值</a>
</body>
</html>
<span style="color:#000000;"><%@page language="java" contenttype="text/html;charset=gb2312"%>
<!doctype html>
<html>
<head>
<title>取得cookie的值</title>
</head>
<body>
cookie中的username的值为：${cookie.username.value}
</body>
</html>
header内置对象
<!doctype html>
<html>
<head>
<title>取得header的值</title>
</head>
<body>
${header["host"]}<br />
${header["user-agent"]}<br />
</body>
</html>
initparam内置对象:获取web站点中设置的环境变量
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<!doctype html>
<html>
<head>
<title>获得环境参数</title>
</head>
<body>
username参数值：${initparam.username}<br />
</body>
</html>
<?xml version="1.0" encoding="iso-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/xmlschema-instance"
xsi:schemalocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
version="2.5">
<context-param>
<param-name>username</param-name>
<param-value>zhangdapeng</param-value>
</context-param>
</web-app>
pagecontex内置对象
用来取得有关用户请求和页面的详细信息
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<!doctype html>
<html>
<head>
<title>pagecontext演示</title>
</head>
<body>
<table border="1">
<tr>
<td>取得请求的参数的字符串</td>
<td>${pagecontext.request.querystring}</td>
</tr><tr>
<td>取得请求url</td>
<td>${pagecontext.request.requesturl}</td>
</tr><tr>
<td>取得web应用名称</td>
<td>${pagecontext.request.contextpath}</td>
</tr><tr>
<td>取得http请求方式（post/get）</td>
<td>${pagecontext.request.method}</td>
</tr><tr>
<td>取得使用的协议</td>
<td>${pagecontext.request.protocol}</td>
</tr><tr>
<td>取得用户ip地址</td>
<td>${pagecontext.request.remoteaddr}</td>
</tr><tr>
<td>判断session是否为新</td>
<td>${pagecontext.session.new}</td>
</tr><tr>
<td>取得session的id</td>
<td>${pagecontext.session.id}</td>
</tr>
</table>
</body>
</html>
el存取器:
使用存取器读取javabean中的数据
package com.javaweb.ch08;
import java.util.*;
//一个简单的javabean示例
public class person{
//name属性
private string name;
//age属性
private int age;
//sex属性
private string sex;
//friends属性
private arraylist friends;
//无参构造方法
public person(){
}
//自定义构造的方法
public person(string name,int age,string sex){
this.name = name;
this.age = age;
this.sex = sex;
}
//获取name的属性值
public string getname(){
return name;
}
//获取age属性值
public int getage(){
return age;
}
//获取sex的属性值
public string getsex(){
return sex;
}
//设置name的属性
public void setname(string name){
this.name = name;
}
//设置age的属性值
public void setage(int age){
this.age = age;
}
//设置sex的属性值
public void setsex(string sex){
this.sex = sex;
}
//设置friends的值
public void setfriends(arraylist friends){
this.friends = friends;
}
//获取friends的属性值
public arraylist getfriends(){
return friends;
}
}
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<%@page import="java.util.*,com.javaweb.ch08.*" %>
<!doctype html>
<html>
<head>
<title>设置javabean中的属性</title>
</head>
<body>
<%
//实例化一个person
person person = new person("zhangdapeng",24,"男");
//创建一个friends实例
arraylist friends = new arraylist();
//添加值
friends.add("wang wu");
friends.add("li si");
person.setfriends(friends);
//存储在session范围内
session.setattribute("person",person);
%>
<a href="getjavabean.jsp">跳转到getjavabean.jsp</a>
</body>
</html>
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<!doctype html>
<html>
<head>
<title>取得javabean中的属性值</title>
</head>
<body>
姓名：${sessionscope.person.name}<br />
年龄：${sessionscope.person.age}<br />
性别：${sessionscope.person.sex}<br />
朋友：${sessionscope.person.friends[0]},${sessionscope.person.friends[1]}<br />
</body>
</html>
使用存储器读取map中的数据
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<%@page import="java.util.*,com.javaweb.ch08.*" %>
<!doctype html>
<html>
<head>
<title>设置map页面</title>
</head>
<body>
<%
//新建一个hashmap
hashmap userinfo = new hashmap();
//在hashmap中设置值
userinfo.put("username","zhangdapeng");
userinfo.put("password","zhnagda123");
//将值存储到session范围中
session.setattribute("userinfo",userinfo);
%>
<a href="getmapdemo.jsp">跳转到getmapdemo.jsp</a>
</body>
</html>
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<!doctype html>
<html>
<head>
<title>使用存储器读取map中的数据</title>
</head>
<body>
用户名：${sessionscope.userinfo.username}<br />
密码：${sessionscope.userinfo.password}<br />
</body>
</html>
使用存储器读取数组中的数据
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<%@page import="java.util.*,com.javaweb.ch08.*" %>
<!doctype html>
<html>
<head>
<title>设置array页面</title>
</head>
<body>
<%
string[] names = {"zhangda1","zhangda2","zhangda3"};
//将值存储到session范围中
session.setattribute("names",names);
%>
<a href="getmapdemo.jsp">跳转到getarraydemo.jsp</a>
</body>
</html>
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<!doctype html>
<html>
<head>
<title>使用存储器读取map中的数据</title>
</head>
<body>
用户名1：${sessionscope.names[0]}<br />
用户名2：${sessionscope.names[1]}<br />
</body>
</html>
存储器的复杂应用
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<%@page import="java.util.*,com.javaweb.ch08.*" %>
<!doctype html>
<html>
<head>
<title>设置array页面</title>
</head>
<body>
<%
arraylist<person> persons = new arraylist<person>();
person person1 = new person("wang wu",24,"男");
person person2 = new person("wang liu",24,"女");
persons.add(person1);
persons.add(person2);
session.setattribute("persons",persons);
%>
<a href="getmapdemo.jsp">跳转到getarraydemo.jsp</a>
</body>
</html>
<%@page language="java" contenttype="text/html;charset=gb2312"%>
<!doctype html>
<html>
<head>
<title>使用存储器读取map中的数据</title>
</head>
<body>
用户名1：${sessionscope.persons[0].name},${sessionscope.persons[0].age},${sessionscope.persons[0].sex}<br />
用户名2：${sessionscope.persons[1].name},${sessionscope.persons[1].age},${sessionscope.persons[1].sex}<br />
</body>
</html>
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