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 ：${requestScope.number}<br> session ：${sessionScope.use}<br> application ：${applicationScope.string}<br><br> ${wa}<br> <% request.removeAttribute("wa"); //将request域中"wa"给删除 %> ${wa}<br> </body> </html>
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; } }
<%@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()} <br> ${user.username} <br> <hr> <!-- 从Map中存储数据 --> <% Map<String,String>map = new HashMap<String,String>(); map.put("name","Gary2"); map.put("age","12"); request.setAttribute("user2",map); %> ${user2.name}<br> ${user2.age}<br> </body> </html>
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
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; } }
<%@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} <br> ${list[4].username} <br> 加减运算 ${list[2].age+list[4].age} <br> 判空list ${empty list} <br> 判空list2 ${empty list2} <br> ${pageContext.request.contextPath} <br> </body> </html>
输出
作用域：page request session application
Gary2
Gary4
加减运算 80
判空list false
判空list true
/Gary04
获得当前项目路径可以通过EL表达式Page作用域去获取
${pageContext.request.contextPath}