EL学习笔记

最新推荐文章于 2025-09-04 16:57:43 发布

baiymfkese

最新推荐文章于 2025-09-04 16:57:43 发布

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文章标签： string jsp stylesheet html user date

本文介绍了JSPEL的各种运算符，包括算术型、逻辑型、关系型和条件型等，并展示了如何在JSP页面中使用JSPEL来访问JavaBeans、数组、List和Map等类型的对象，还详细说明了JSPEL的内容对象以及如何设置JSP不使用JSPEL。

一、 JSP EL 的运算符

类型	定义
算术型	*+ - / div % mod**
逻辑型	and && or \|\| not !
关系型	== eq != ne > gt < lt >= ge <= le
条件型	a?b:c
空	empty

二、 JSP EL 的基本用法

类型	实例	基本调用方法
JavaBeans	${user.username} ${user["username"]} ${user['username']}	user.getUsername()
数组	${sport[1]} ${sport["1"]} ${sport['1']}	sport[1]
List	${phone[2]} ${phone["2"]} ${phone['2']}	phone.get(2)
Map	${phone.home} ${phone["home"]} ${phone['home']}	phone.get("home")

三、 JSP EL 的内容对象

pageContext  当前页面上下文件对象
pageScope  page对象
requestScope  request对象
sessionScope  session对象
applicationScope  application对象
param  得到页面传来的参数
paramValues  得到页面传来的多个参数，返回一个数组
header  获取头信息
headerValues  获取头信息的值
cookie  获取cookie对象的值
initParam  获取设定初始的参数值

例：

< %=session.getAttribute( "phone")%>

等价于${sessionScope.phone}

四、如何设置 JSP 不使用 JSP EL

1 、当前页面不要用 JSP EL

< %@page isELIgnored ="true" %>

2 、整个 web 应用都不使用 EL ，修改 web.xml 文件

< web-app... >

 < jsp-config >

 < jsp-property-group >

 < url-pattern > *.jsp</ url-pattern >

 < el-ignored > true</ el-ignored >

 </ jsp-property-group >

 </ jsp-config >

</ web-app... >

五、实例

1 、基本运算符的实例

< %@ page language ="java" pageEncoding ="UTF-8" %>
< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
< html >
 < head >
 < title > My JSP 'elExample1.jsp' starting page</ title >
 < meta http-equiv ="pragma" content ="no-cache" >
 < meta http-equiv ="cache-control" content ="no-cache" >
 < meta http-equiv ="expires" content ="0" >
 < meta http-equiv ="keywords" content ="keyword1,keyword2,keyword3" >
 < meta http-equiv ="description" content ="This is my page" >
 
 </ head >
 < body >
 < !-- 以下为JSP EL的算术运算实例 -- >
 ${10+10 } 
 ${10-10 } 
 ${10*10 } 
 ${10/10 } 
 ${10 div 10 } 
 ${10%10 } 
 ${10 mod 10 } 
 < !-- 以下为想输入原样的表达式，需要用/或者'进行转义 -- >
 /${10+10 } 
 '$'{10+10 } 

 < !-- 以下为JSP EL的关系运算实例 -- >
 ${100>200 } 
 ${100 gt 200 } 
 ${100< 200 } 
 ${100 lt 200 } 
 ${100>=200 } 
 ${100 ge 200 } 
 ${100< =200 } 
 ${100 le 200 } 
 ${100==200 } 
 ${100 eq 200 } 
 ${100 !=200 } 
 ${100 ne 200 } 
 < !-- 以下为比较字符，字符用单引号，字符串用双引号引起 -- >
 ${'e' eq 'h' } 
 ${"hit" > "him" } 

 < !-- 以下为逻辑运算符的实例 -- >
 ${(10>2) && (34>25) } 
 ${(10>2) and (34>25) } 
 ${(10>2) || (34>25) } 
 ${(10>2) or (34>25) } 
 ${!(10>2)} 
 ${not(10>2)} 

 < !-- empty运算符的应用 empty判断时，若对象为""或是null，则都为true-- >
 <%
 pageContext.setAttribute("username",null);
 pageContext.setAttribute("password","");
 pageContext.setAttribute("city","北京");
 pageContext.setAttribute("date",new java.util.Date());
 %>
 < !-- 判断username变量是否为空,以下返回true-- >
 ${empty username } 
 < !-- 判断password变量是否为空，以下返回true -- >
 ${empty password } 
 < !-- 判断city变量是否为空，以下返回false-- >
 ${empty city } 
 < !-- 判断date变量是否为空，以下返回false -- >
 ${empty date } 

 </ body >
</ html >

2 、用 JSP EL 读取 JavaBean 中的值

< %@ page language ="java" pageEncoding ="UTF-8" %>
< %@ page import ="java.util.*,com.meixin.beans.*" %>
< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
< html >
 < head >
 < title > My JSP 'elExample1.jsp' starting page</ title >
 < meta http-equiv ="pragma" content ="no-cache" >
 < meta http-equiv ="cache-control" content ="no-cache" >
 < meta http-equiv ="expires" content ="0" >
 < meta http-equiv ="keywords" content ="keyword1,keyword2,keyword3" >
 < meta http-equiv ="description" content ="This is my page" >
 
 </ head >
 < body >
 < !-- 使用User Bean，设置属性值username -- >
 < jsp:useBean id ="user" class ="com.meixin.beans.User" > </ jsp:useBean >
 < jsp:setProperty name ="user" property ="username" value ="meixin" />
 <%
 //建立Profile对象，设置邮件地址
 Profile p = new Profile();
 p.setEmail("wnight88@sina.com");

 //将不同的电话存入Map中，并设置在p对象的属性中
 Map< String,String > phone = new HashMap< String,String > ();
 phone.put("office","8383838");
 p.setPhone(phone);

 //建立地址对象，设置城市名
 Address address = new Address();
 address.setCity("北京");
 Address[] addresses = {address};
 p.setAddress(addresses);
 user.setProfile(p);
 %>
 < !-- 用JSP EL的级连方式输入值 -- >
 < !-- 输出user对象中的username属性值,三种写法等价 -- >
 ${user.username } 
 ${user["username"] } 
 ${user['username'] } 
 < !-- 输出user对象中profile属性对象中的phone属性Map中键值为office的值 -- >
 ${user.profile.phone.office } 
 ${user['rofile']['phone']['office'] } 
 < !-- 输出user对象中profile属性对象中address数据属性中第0个元素对象中的city的属性值 -- >
 ${user.profile.address[0].city } 
 </ body >
</ html >

以下为对象的JavaBean的内容

1) Profile类

package com.meixin.beans;
import java.util.Date;
import java.util.Map;
public class Profile
{
 private String email;
 private Date birthday;
 private Address[] address;
 private Map<String, String> phone;
 public String getEmail()
 {
 return email;
 }
 public void setEmail(String email)
 {
 this .email = email;
 }
 public Date getBirthday()
 {
 return birthday;
 }
 public void setBirthday(Date birthday)
 {
 this .birthday = birthday;
 }
 public Address[] getAddress()
 {
 return address;
 }
 public void setAddress(Address[] address)
 {
 this .address = address;
 }
 public Map<String, String> getPhone()
 {
 return phone;
 }
 public void setPhone(Map<String, String> phone)
 {
 this .phone = phone;
 }
}

2)User类

package com.meixin.beans;
public class User
{
  private Long userID;
  private String userName;
  private String password;
  private Profile profile;

  public Long getUserID()
  {
    return userID;
  }
  public void setUserID(Long userID)
  {
    this .userID = userID;
  }
  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 Profile getProfile()
  {
    return profile;
  }
  public void setProfile(Profile profile)
  {
    this .profile = profile;
  }

}

3)Address 类

package com.meixin.beans;
public class Address
{
  private String city;
  public String getCity()
  {
    return city;
  }
  public void setCity(String city)
  {
    this .city = city;
  }
}