How to define this simple jsp 2.0 tag

Question

I want to define a very simple JSP 2.0 tag, but don't know how to do.

The tag is used to get the information of a article object in the system. And it's very simple:

<sys:article id="123" var="article">
   Title: ${aritcle.title}
</sys:article>

Then I created a file named article.tag under WEB-INF/tags/, the content is:

<% tag import="sys.App, sys.domains.*" %>
<%@ attribute
    name="id"
    type="java.lang.String"
    required="true"
    description="the id of an article" %>

<%@ attribute
    name="var"
    type="java.lang.String"
    required="true"
    description="let invoker use it to get information" %>

<%
    Article article = App.articleDao.get(id);
%>

// how to set article to the body
<jsp:doBody />

I don't know how to set the retrieved article object to the body, and let it show the title of it.

Answer 1

The key is variable in the tag file.

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

<%@ attribute
  name="id"
  required="true"
  description="the id of article" %>

<%@ attribute
    name="var"
    required="true"
    rtexprvalue="false"
    description="the article object used by invoker" %>

<%@ variable
  name-from-attribute="var"
  description="The alias of passed 'var'"
  alias="aaa"
%> 

<%
 Article article = getArticleById(id);
 request.setAttribute("article", article);
%>

<c:set var="aaa" value="${article}" />