cewolf怎么显示不出图象？？

<%@page contentType="text/html; charset=GBK"%>
<%@page import="java.util.*"%>
<%@page import="de.laures.cewolf.*"%>
<%@page import="org.jfree.data.*"%>
<%@page import="org.jfree.data.time.*"%>
<%@page import="org.jfree.chart.tooltips.*"%>
<%@page import="org.jfree.chart.*"%>
<%@page import="org.jfree.chart.plot.*"%>
<%@page import="org.jfree.chart.axis.*"%>
<%@taglib uri='/WEB-INF/cewolf.tld' prefix='cewolf' %>
<%
   DatasetProducer xyData=new DatasetProducer(){
     public Object produceDataset(Map params){
       XYSeries xys=new XYSeries("java 从入门到精通");
       for(int i=1;i<=30;i++){
         double y=1+(int)(Math.random()*20);
         xys.add((double)i,y);
         }
         return new XYSeriesCollection(xys);
       }
       public String getProducerId(){
           return "XYDataProducer";
         }
       public boolean hasExpired(Map params,Date since){
           return true;
         }
   };
       pageContext.setAttribute("xyData",xyData);
%>
<p>
<cewolf:chart
    id="XYChart"  type="xy"
    xaxislabel="2004年6月" yaxislabel="日销售量（本）"
    title="编程图书日销售量统计图（线段图）">
    <cewolf:colorpaint color="ffff99"/>
    <cewolf:data>
            <cewolf:producer id="xyData"/>
    </cewolf:data>
</cewolf:chart>
<cewolf:img
    chartid="XYChart"
    renderer="/cewolf"
    width="500"
    height="500">
</cewolf:img>
<p>

<p class="indent">

<cewolf:img    chartid="XYChart"    renderer="/cewolf"    width="500"    height="500"></cewolf:img><p>
<p class="indent">