el表达式

<%
    pageContext.setAttribute("name","page");
    request.setAttribute("name","request");
    session.setAttribute("name","session");
    application.setAttribute("name","application");

%>
${name}<!—会在四大域中从小到大的查询，找到第一个就终止查询-->
${pageScope.name}
${requestScope.name}
${sessionScope.name}
${applicationScope.name}

${param.name}  (也可以接受表单提交的数据)
（http://localhost:8080/WebTest/el1.jsp?name=haoren）
接受一组的参数
提交端
<form action="/WebTest/el1.jsp" method="post">
    <input type="checkbox" name="enjoy"  value="打架" checked="checked">打架
    <input type="checkbox" name="enjoy"  value="打人">打人
    <input type="checkbox" name="enjoy"  value="打球">打球
    <input type="submit" value="提交">
</form>
接收端
<%request.setCharacterEncoding("UTF-8"); %>
${paramValues.enjoy[0]}
${paramValues.enjoy[1]}
${paramValues.enjoy[2]}

<%
    List list = new ArrayList();
        list.add("中国");
        list.add("美国");
        list.add("英国");
        request.setAttribute("ha",list);
%>
    ${ha[0]}
    ${ha[1]}

<%--map 的赋值形式是key value 取值的时候推荐用[]--%>
<%
    Map map = new HashMap();
    map.put("age1","12");
    map.put("age2","16");
    map.put("age3","14");
    request.setAttribute("is",map);
%>
    ${is.age1}
    ${is["age2"]}
    ${is["age3"]}

<%--在 el表达式中取map对象的方法--%>
<%
    Person person = new Person();
        Map map1 = new HashMap();
            map1.put("p1",new Person("huairen"));
            map1.put("p2",new Person("haoren"));
        request.setAttribute("c1",map1);
%>
    ${c1.p1.name}
    ${c1.p2.name}

<%--测试list数组的--%>
    <%
        List<Person> personlist =new ArrayList<Person>();
            personlist.add(new Person("duang"));
            personlist.add(new Person("bomsm"));
            request.setAttribute("bom",personlist);
    %>
${bom[0].name}
${bom[1].name}

private String name;

private String  name;
private String  gender;
private List<Person> person;

   private String name;
    private List<Employee> employee;

 List<Person> lists = new ArrayList<Person>();
            lists.add(new Person("测试1"));
            lists.add(new Person("测试2"));
        Employee employee1 = new Employee("张三","男",lists);
        Employee employee2 = new Employee("娜娜","女",lists);
        List<Employee> list2 = new ArrayList<Employee>();
            list2.add(employee1);
            list2.add(employee2);
        DepartmentDemo list3 = new DepartmentDemo();
            list3.setName("部门1");
            list3.setEmployee(list2);
            request.setAttribute("list3",list3);
            request.getRequestDispatcher("/el.jsp").forward(request,response);

   <%--${lists[1].name}--%>
    <%--${list2[0].name}--%>
${list3.employee[0].name}
${list3.employee[0].person[0].name}

package com.java.bean;

public class FunctionDemo {
    public static String toUpperCase(String str){
        return str.toUpperCase();
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
        version="2.0">
    <tlib-version>1.0</tlib-version>
    <short-name>myfn</short-name>
    <uri>http://www.blackhwcf.cn/myfn</uri>
    <function><!-- 定义函数 -->
        <name>toUppercase</name>
        <function-class>com.java.bean.FunctionDemo</function-class>
        <function-signature>java.lang.String toUpperCase( java.lang.String )</function-signature>
    </function>
</taglib>

   <jsp-config>
        <taglib>
            <taglib-uri>http://www.blackhwcf.cn/myfn</taglib-uri>
            <taglib-location>/WEB-INF/dio.tld</taglib-location>
        </taglib>
    </jsp-config>

<%@ taglib uri="http://www.blackhwcf.cn/myfn" prefix="myfn"%>

<%--测试自定义 函数 功能 ：全部转换成大写--%>
${myfn:toUppercase("yyyyyy")}