java web

java web

文章目录

一._ EL _

1.做运算2.el表达式只能从域对象中获取值3.获取对象 list集合，map集合的值

1.对象：$ {域名称.键名.属性名}2.list集合：$ {域名称.键名[索引]}3.map集合 二.JSTL

1.foreach2.choose(相当于switch)3.if 三.三层架构

一._ EL _

作用：替换和简化jsp页面中java代码的编写
语法：${表达式}

1.做运算

${3>4} 结果为false
${6+7} 结果为13

2.el表达式只能从域对象中获取值

语法：
1.$ {域名称.键名}：从指定域中获取指定键的值
域名称：pageScope --> pageContext
举例：在request域中存储了name=张三
获取：$ {requestScope.name}

<%--
  Created by IntelliJ IDEA.
  User: cll
  Date: 2022/1/21
  Time: 13:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

  
    

  
  <%
    request.setAttribute("name","李四");
  %>
  ${requestScope.name};

显示：

李四;

2.{键名}：表示依次从最小的域中查找是否有该键对应的值，直到找到为止

%--
  Created by IntelliJ IDEA.
  User: cll
  Date: 2022/1/21
  Time: 13:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

  
    

  
  <%
    session.setAttribute("name","李四");

    request.setAttribute("name","张三");

  %>
     ${name};

显示：

张三;

3.获取对象 list集合，map集合的值 1.对象：$ {域名称.键名.属性名}

本质上会去调用对象的getter方法

package com.kuang.pojo;

import java.text.SimpleDateFormat;
import java.util.Date;

public class Userel {
    private String name;
    private int age;
    private Date birthday;
    public String getBitStr(){
        if(birthday!=null){
            //格式化日期对象
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            return simpleDateFormat.format(birthday);
        }
        else{
            return "";
        }
    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
}

<%@ page import="com.kuang.pojo.Userel" %>
<%@ page import="java.util.Date" %><%--
  Created by IntelliJ IDEA.
  User: cll
  Date: 2022/1/21
  Time: 13:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

  
    

  
  <%
    Userel user=new Userel();
    user.setName("张三");
    user.setAge(19);
    user.setBirthday(new Date());
    request.setAttribute("u",user);

  %>
  <%-- --%>
     ${u.age}
${requestScope.u.name}
  ${u.birthday}
  ${u.bitStr}

19 张三 Fri Jan 21 15:02:26 CST 2022 2022-01-21 15:02:26

2.list集合：$ {域名称.键名[索引]}

<%@ page import="com.kuang.pojo.Userel" %>
<%@ page import="java.util.Date" %>
<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %><%--
 Created by IntelliJ IDEA.
 User: cll
 Date: 2022/1/21
 Time: 13:20
 To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

 
   

 
 <%
   Userel user=new Userel();
   user.setName("张三");
   user.setAge(19);
   user.setBirthday(new Date());
   request.setAttribute("u",user);
   List list=new ArrayList();
   list.add("aaa");
   list.add("ccc");
   list.add("kkk");
   list.add(user);
   request.setAttribute("list",list);

 %>
 <%-- --%>
    ${list}
   ${list[1]}
 ${list[0]}
 ${list[3].name}

显示：

[aaa, ccc, kkk, com.kuang.pojo.Userel@1342c24] ccc aaa 张三

3.map集合

${域名称.键名.key名称}
${域名称.键名[“key名称”]}

<%@ page import="com.kuang.pojo.Userel" %>
<%@ page import="java.util.*" %><%--
  Created by IntelliJ IDEA.
  User: cll
  Date: 2022/1/21
  Time: 13:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

  
    

  
  <%
    Userel user=new Userel();
    user.setName("张三");
    Map map=new HashMap();
    map.put("name","李四");
    map.put("age",18);
    map.put("user",user);
    request.setAttribute("map",map);

  %>
  <%-- --%>
${map.name}
  ${map.age}
  ${map.user.name}

显示：

李四 18 张三

二.JSTL 1.foreach

<%@ page import="com.kuang.pojo.Userel" %>
<%@ page import="java.util.*" %><%--
  Created by IntelliJ IDEA.
  User: cll
  Date: 2022/1/21
  Time: 13:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

  
    

  
  <%
    List list=new ArrayList();
    list.add("aaa");
    list.add("bbb");
    list.add("ccc");
    request.setAttribute("list",list);
  %>
  <%-- --%>

  ${s.index} ${s.count} ${str} 

0 1 aaa
1 2 bbb
2 3 ccc

 
    ${i} ${s.index} ${s.count}

  

1 1 1
3 3 2
5 5 3
7 7 4
9 9 5

2.choose(相当于switch)

<%
request.setAttribute("number",5);
%>

    星期一
    星期二
    星期三
    星期四
    星期五
    星期六
    星期天
    数字输入有误
  

星期五

3.if

<%
request.setAttribute("number",5);
%>

    我
  

    ${number}为奇数
  

我
5为奇数

<%@ page import="com.kuang.pojo.Userel" %>
<%@ page import="java.util.*" %><%--
  Created by IntelliJ IDEA.
  User: cll
  Date: 2022/1/21
  Time: 13:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

  
    

  
  <%
    List list=new ArrayList();
    list.add(new Userel("张三",18,new Date()));
    list.add(new Userel("李四",19,new Date()));
    list.add(new Userel("王五",20,new Date()));
    request.setAttribute("list",list);
  %>
  <%-- --%>
  
    
      编号
      姓名
      年龄
      生日
    
    
      
        
          ${s.count}
          ${user.name}
          ${user.age}
          ${user.birStr}
        
      

      
        
          ${s.count}
          ${user.name}
          ${user.age}
          ${user.birStr}
        
      
    
  

三.三层架构