EL表达式（一）

EL表达式:
　　它不是一门语言，只是jsp的表达式
　　EL表达式只能获取四大域中的数据(pageContext,request,session,application)
EL表达式：获取对象的get方法。
基本语法：${EL表达式}
如果EL表达式获取的对象为NULL，页面不会显示数据，EL表达式永远不会出现空指针。

11个隐式对象:
　　pageContext
　　pageScope 从page范围内取数据
　　requestScope
　　sessionScope
　　applicationScope
　　param 接收传递到本页面的参数
　　paramValues 接收传递到本页面的一组参数
　　header 一个头信息数据
　　headerValues 一组头信息数据
　　cookie cookie中的数据
　　initParam 取得配置的初始化参数
运算符"."和"[]" : "."能做的"[]"也能做，"[]"能做的"."不一定能做

<jsp:useBean id="实例化对象名称" scope="对象保存的属性范围（4种）" class="包全名.类全名（按住Ctrl鼠标单击可进入对应Java程序）" ></jsp:useBean>
设置对象<jsp:setProperty name="实例化对象名称(id)" property="*" > 自动匹配
设置对象<jsp:setProperty name="实例化对象名称(id)" property="属性名称" /> 指定属性
设置对象<jsp:setProperty name="实例化对象名称(id)" property="属性名称" param="参数"/> 指定参数
设置对象<jsp:setProperty name="实例化对象名称(id)" property="属性名称" value="内容"/> 制定内容
获取对象<jsp:getProperty name="实例化对象名称(id)" property="属性名称" />

1.java

 1 package cn.gs.ly.mvc.domain;
 2 
 3 import java.util.Date;
 4 
 5 public class Person {
 6     private String name;
 7     private String gender;
 8     private boolean married;
 9     private Date birthday;
10     private Address address = new Address();
11     
12     public Person() {
13         
14     }
15     
16     public Person(String name, String gender, boolean married) {
17         super();
18         this.name = name;
19         this.gender = gender;
20         this.married = married;
21     }
22     
23     
24     public Address getAddress() {
25         return address;
26     }
27 
28     public void setAddres(Address address) {
29         this.address = address;
30     }
31 
32     public String getName() {
33         return name;
34     }
35     public void setName(String name) {
36         this.name = name;
37     }
38     public String getGender() {
39         return gender;
40     }
41     public void setGender(String gender) {
42         this.gender = gender;
43     }
44     public boolean isMarried() {
45         return married;
46     }
47     public void setMarried(boolean married) {
48         this.married = married;
49     }
50     public Date getBirthday() {
51         return birthday;
52     }
53     public void setBirthday(Date birthday) {
54         this.birthday = birthday;
55     }
56     
57 }

 1 package cn.gs.ly.mvc.domain;
 2 
 3 public class Address {
 4     private String city="青岛";
 5 
 6     public String getCity() {
 7         return city;
 8     }
 9 
10     public void setCity(String city) {
11         this.city = city;
12     }
13     
14 }

2.jsp

 1 <%@page import="java.util.HashMap"%>
 2 <%@page import="java.util.Map"%>
 3 <%@page import="java.util.ArrayList"%>
 4 <%@page import="java.util.List"%>
 5 <%@page import="cn.gs.ly.mvc.domain.Person"%>
 6 <%@ page language="java" contentType="text/html" pageEncoding="UTF-8"%>
 7 <!DOCTYPE html>
 8 <html>
 9 <head>
10 <title>Insert title here</title>
11 </head>
12 <body>
13     <jsp:useBean id="p" class="cn.gs.ly.mvc.domain.Person"></jsp:useBean>
14     <jsp:setProperty property="name" name="p" value="刘超"></jsp:setProperty>
15     <!--获得属性三种方法 -->
16     方法1：<%=p.getName() %><br/>
17     方法2：<jsp:getProperty property="name" name="p" ></jsp:getProperty> <br/>
18     方法3：${p.name }====${p["name"]}====${p['name']}<hr/>    
19         
20     获取未赋值的gender1：<%=p.getGender() %><br/>
21     获取未赋值的gender2：<jsp:getProperty property="gender" name="p" ></jsp:getProperty> <br/>
22     获取未赋值的gender3：${p.gender }<hr/>
23 
24     获得没有的对象：${p1.gender }<hr/>
25     
26     <%
27         //依次从page-request-session-application 取值，都没有为空白
28         pageContext.setAttribute("pp", "pp1");
29         pageContext.setAttribute("pp", "pp2",pageContext.REQUEST_SCOPE) ;
30         session.setAttribute("pp", "pp3");
31         application.setAttribute("pp", "pp4");
32     %>
33     1：${pp}     
34     2：${requestScope.pp}
35     3：${pp} 
36     4：${pp}  
37     5：${pp}      
38      <hr/>
39         
40     ${p.address.city}<hr/>
41     ${p["class"]}<hr/>
42     
43     <jsp:setProperty property="married" name="p" value="true"></jsp:setProperty>
44     ${p.married }<hr/>
45     
46     ${pageContext.request.remoteAddr}<hr/>
47     ${pageContext.session.id}<hr/>
48     ${pageContext.request.method}<hr/>
49     ${pageContext.request.localName}<hr/>
50     
51     <%
52         String str[] = {"数组元素a","数组元素b","数组元素c"};
53         pageContext.setAttribute("s", str);
54         
55         List list =new ArrayList();
56         list.add("list集合元素a");
57         list.add("list集合元素b");
58         list.add("list集合元素c");
59         pageContext.setAttribute("list", list);
60         
61         Map map = new HashMap();
62         map.put("a","map集合aa");
63         map.put("b","map集合bb");
64         map.put("c","map集合cc");
65         pageContext.setAttribute("map", map);
66         
67         Map map1 = new HashMap();
68         map.put("1","map集合aa1");
69         map.put("2","map集合bb2");
70         map.put("3","map集合cc3");
71         pageContext.setAttribute("map1", map);
72         
73         Map map2 = new HashMap();
74         map.put("1",new Person("刘超","男",false ));
75         map.put("2",new Person("姜静","女",false ));
76         map.put("3",new Person("王熙","男",true ));
77         pageContext.setAttribute("map2", map);
78      %>
79     ${s[0]}<hr/>
80     ${list[0]}<hr/>
81     ${map.a}<hr/>
82     ${map["1"]}<hr/>
83     ${map2["3"].name}<hr/>
84     
85     <!-- 
86     浏览器出入下面网址(明文提交) 可获取明文提交的 参数
87     http://localhost:8080/WEB2018/Demo01.jsp?ref=liuyang&inst=inst1&inst=inst2&inst=inst3     
88     -->
89     获取明文提交的参数方法1：<%=request.getParameter("ref") %>
90     获取明文提交的参数方法2：${param.ref}<hr/>
91     获取明文提交的多个参数方法：${paramValues.inst[0] } ${paramValues.inst[1] }<hr/>
92

　${headerValues["accept"][0]}<hr/>
　　　 ${header["accept-encoding"] }<hr/>
　
Cookie:${cookie}<hr/>
Cookie_name:${cookie["JSESSIONID"].name }<hr/>
Cookie_value:${cookie["JSESSIONID"].value }<hr/>

获得xml初始化参数：${initParam["info"]}<br/>

93 <input type="text" value="${p.address.city}">

94     
95 </body>
96 </html>

3.web.xml 初始化配置

1 <context-param><!-- 初始化参数 -->
2 <param-name>info</param-name>
3 <param-value>value_liuyang</param-value>
4 </context-param>

4.运行结果