JavaWeb-EL入门

一.EL表达式

　　1.EL是JSP内置的表达式语言

　　2.从JSP2.0开始，不让再使用java脚本，用EL和动态标签来代替java脚本

　　3.EL替代的是java脚本的<%= .... %>，没错只能用于输出

　　4.最常用的是：

　　　　（1）全域查找；比如：request.setAttribute("xxx","XXX")，而通过 ${ xxx }就可以查找到XXX

　　　　（2）指定域查找；比如：${ requestScope.xxx },在request域中查找

　　5.JavaBean导航，上代码：

package cn.itcase.domain;

//员工类
public class Employee {
    private String name;
    private String age;
    private Address addr;
    public Employee() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Employee(String name, String age, Address addr) {
        super();
        this.name = name;
        this.age = age;
        this.addr = addr;
    }
    @Override
    public String toString() {
        return "Employee [name=" + name + ", age=" + age + ", addr=" + addr + "]";
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAge() {
        return age;
    }
    public void setAge(String age) {
        this.age = age;
    }
    public Address getAddr() {
        return addr;
    }
    public void setAddr(Address addr) {
        this.addr = addr;
    }
    
    
}

package cn.itcase.domain;

//地址类
public class Address {
    private String country;
    private String city;
    public Address() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Address(String country, String city) {
        super();
        this.country = country;
        this.city = city;
    }
    public String getCountry() {
        return country;
    }
    public void setCountry(String country) {
        this.country = country;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    
}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="cn.itcase.domain.*"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <%
        //设置城市
        Address addr = new Address();
        addr.setCity("广州");
        addr.setCountry("中国");
    
        //设置员工
        Employee emp =  new Employee();
        emp.setName("张三");
        emp.setAge("14");
        emp.setAddr(addr);
        
        //保存到request域中
        request.setAttribute("emp", emp);    
    %>
    
    //最终得到city的值
    ${ requestScope.emp.addr.city }
    
    
</body>
</html>