JavaWeb_EL表达式存储数据及获得项目路径

提示：扫一扫查出行
【扫一扫了解最新限行尾号】
复制提示

菜鸟教程传送门

EL表达式【百度百科】：EL（Expression Language）是为了使JSP写起来更加简单。表达式语言的灵感来自于 ECMAScript 和 XPath 表达式语言，它提供了在 JSP 中简化表达式的方法，让Jsp的代码更加简化

EL表达式获得当前项目路径可以通过Page作用域去获取

${pageContext.request.contextPath}

操作简单数据

<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Insert title here</title>
</head>
<body>
作用域：page request session application
<hr>
<%
request.setAttribute("number",2000);
session.setAttribute("use","Hello Gary!!!");
application.setAttribute("string","nihao");//同名情况直接使用${wa}只会从request->session->application
request.setAttribute("wa",1);
session.setAttribute("wa",2);
application.setAttribute("wa",3);
%>request ：${requestScope.number} 
session ：${sessionScope.use} 
application ：${applicationScope.string} ${wa} <%
request.removeAttribute("wa"); //将request域中"wa"给删除
%>${wa} 
</body>
</html>

el.jsp

输出：

作用域：page request session application
request ：2000
session ：Hello Gary!!!
application ：nihao 1
2

el表达式从map集合和对象里面取得数据

package com.Gary.model;public class User {
private String username;
private String password;
private int age;
private String sex;
private boolean isAdmin=false; //判断是否是管理员账号 public User(String username, String password, int age, String sex, boolean isAdmin) {
super();
this.username = username;
this.password = password;
this.age = age;
this.sex = sex;
this.isAdmin = isAdmin;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public boolean isAdmin() {
return isAdmin;
}
public void setAdmin(boolean isAdmin) {
this.isAdmin = isAdmin;
}}

User.java

<%@page import="java.util.HashMap"%>
<%@page import="java.util.Map"%>
<%@page import="com.Gary.model.User"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Insert title here</title>
</head>
<body>
作用域：page request session application
<hr><%
User u = new User("Gary","123",20,"男",false);
request.setAttribute("user",u);
%>${user.getUsername()} 
${user.username} <hr>

<%
Map<String,String>map = new HashMap<String,String>();
map.put("name","Gary2");
map.put("age","12");
request.setAttribute("user2",map);
%>${user2.name} 
${user2.age} </body>
</html>

el.jsp

输出：

作用域：page request session application
Gary
Gary Gary2
12

如果要使用 ${user.username} 去替代 ${user.getUsername()} 那么User.java中必须要存在 getUsername() 方法

el表达式从list集合和对象里面取得数据

User.java

<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@page import="java.util.HashMap"%>
<%@page import="java.util.Map"%>
<%@page import="com.Gary.model.User"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Insert title here</title>
</head>
<body>
作用域：page request session application
<hr><%
List<User> list = new ArrayList<User>();
list.add(new User("Gary0","0",10,"男",false));
list.add(new User("Gary1","1",20,"男",false));
list.add(new User("Gary2","2",30,"男",false));
list.add(new User("Gary3","3",40,"男",false));
list.add(new User("Gary4","4",50,"男",false));
request.setAttribute("list", list);
%>${list[2].username} 
${list[4].username} 加减运算 ${list[2].age+list[4].age} 判空list ${empty list} 
判空list2 ${empty list2} ${pageContext.request.contextPath} 
</body>
</html>