How JSP assigns values to tags

question:

JSP has variable  String filterString =(String)request.getParameter("filter");

If you set the value directly with jsp, a compilation error will be reported, saying that % cannot be used in the tag:

<t:datagrid name="type" title="Demo" actionUrl="controller.do?<%=filter%>" idField="id" treegrid="true" pagination="false">

Changed to ${filter} , but the value is empty

<t:datagrid name="type" title="Demo" actionUrl="controller.do?${filter}" idField="id" treegrid="true" pagination="false">

 

Correct solution:

Assignment via the c tag.

String filterString =(String)request.getParameter("filter");

<c:set var="filter" value="<%=filterString%>"/>

<t:datagrid name="type" title="Demo" actionUrl="controller.do?${filter}" idField="id" treegrid="true" pagination="false">