EL表达式的11隐含对象

EL表达式在不同范围如何取值：

<%
        pageContext.setAttribute("book", "红楼梦");
        request.setAttribute("book", "水浒传");
        session.setAttribute("book", "三国演义");
        application.setAttribute("book", "西游记");
    %>
    <!-- 当key值相同的时候，并且没有指明在什么范围内取值的话，会取最小范围内的值返回 -->
    ${book }
    <br/>
    <!-- 获取不同范围内的值 -->
    pageScope:${pageScope.book }
    <br />
    requestScope:${requestScope.book }
    <br />
    sessionScope:${sessionScope.book }
    <br />
    applicationScope:${applicationScope.book }
    <br />
    <hr/>
    <input type="text" value = "${pageScope.book }" />
    <input type="text" value = "${pageScope['book']}" />
    <input type = "text" value = "<%=request.getParameter("user_id")==null?"":request.getParameter("user_id") %>"  /><br/>
   param:相当于request.getParameter("user_id"); <input type= "text" value = "${param.user_id }" /><br/>
   paramValues(一key多值):相当于request.getParameterValues("user_id");<input type = "text" value= "${paramValues }" />