EL表达式

EL

获取page、request、session、application对象中的数据

• 语法：${}
• 读取顺序：page>request>session>application

    <%
        pageContext.setAttribute("name","page");
        request.setAttribute("name","request");
        session.setAttribute("name","session");
        application.setAttribute("name","application");
    %>
    ${name} ---结果为page

• 特殊读取：$

    ${requestScope.name}
    ${pageScope.name}
    ${sessionScope.name}
    ${applicationScope.name}

• 使用注意：只能使用在jsp页面
• 及联获取：可获取对象的属性，但必须要有get方法，${user.xxxx}或者$

    <%
        User user = new User("1","claudxyz",20);

        pageContext.setAttribute("user",user);
    %>

    ${user}

    <table border="1">
        <tr>
            <th>用户号</th>
            <th>姓名</th>
            <th>年龄</th>
        </tr>
        <tr>
            <td>${user.id}</td>
            <td>${user.name}</td>
            <td>${user.age}</td>
        </tr>
    </table>

• EL执行表达式
  && || ! != == < > <= >=

&& and
|| or
! not
== eq
!= ne
< lt
> gt
<= le
>= ge
empty