实例解析JSP中EL表达式的各种运用-巨人网络通讯

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${1!=1}/td>
      /tr>
      tr>
        td>小于运算符\${1 lt; 2}/td>
        td>结果${1  2}/td>
      /tr>
      tr>
        td>大于运算符\${3 gt; 2}/td>
        td>结果${3 > 2}/td>
      /tr>
      tr>
        td>小于等于运算符\${1 lt;= 2}/td>
        td>结果${1 = 2}/td>
      /tr>
      tr>
        td>大于等于运算符\${3 gt;= 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>\${21?"Yes":"No"}/td>
        td>结果${21?"Yes":"No"}/td>
      /tr>
    /table>
    table border=1>
      tr>
        td>验证运算符/td>
        td>结果/td>
      /tr>
      tr>
        td>\${empty param.username}/td>
        td>结果${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>
    %
      ArrayListPerson> persons = new ArrayListPerson>();
       
      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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