JSP EL表达式 


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%--        EL表达式  默认值空 不是null
              操作域对象中的数据 不能局部变量
              从小到大去找--%>
    <%
        //设置数据
        pageContext.setAttribute("name1","pageC");

        request.setAttribute("name2","req");

        session.setAttribute("name3","sess");

        application.setAttribute("name4","app");
    %>
<%--    获取数据--%>
    ${"name"}
<%--    获取指定范围--%>
    ${pageScope.name1}
    ${requestScope.name2}
    ${sessionScope.name3}
    ${applicationScope.name4}
</body>
</html>

<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page import="java.util.Map" %>
<%@ page import="java.util.HashMap" %>
<%@ page import="bean.User" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <%
        List<String> list=new ArrayList<>();
        list.add("aaa");
        list.add("bbb");
        request.setAttribute("list",list);

        Map map=new HashMap();
        map.put("bbb",111);
        request.setAttribute("map",map);

        //JavaBean 必须提供get方法
        User user=new User("String");
        request.setAttribute("user",user);
    %>
<%--    获取集合值--%>
    ${list.size()}<br>
    ${list[1]}<br>

    ${map.bbb}<br>
    ${map[bbb]}<br>
<%--javabean--%>
    ${user}<br>
    ${user.name}<br>
    ${user.getName()}

</body>
</html>


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

    <%
        request.setAttribute("str1","");
        request.setAttribute("str2","str2");
        request.setAttribute("str3",null);


    %>

<%--    empty 判断域对象是否为空
              有值为false
              空 null都为true
                --%>
    ${empty str1}<br>
    ${empty str3}<br>
    ${empty str2}<br>
    ${empty str4}<br>
</body>
</html>
posted @ 2022-04-21 17:35  lwx_R  阅读(23)  评论(0)  编辑  收藏  举报