会使用JFREECHAERT的来看看

<%@ page contentType="text/html;charset=GBK"%> 
<%@ page import="org.jfree.data.general.DefaultPieDataset"%> 
<%@ page import="org.jfree.chart.*"%> 
<%@ page import="org.jfree.chart.plot.*"%> 
<%@ page import="org.jfree.chart.servlet.ServletUtilities"%> 
<%@ page import="org.jfree.chart.urls.StandardPieURLGenerator"%> 
<%@ page import="org.jfree.chart.entity.StandardEntityCollection"%> 
<%@ page import="java.io.*"%> 
<HTML> 
<HEAD> 
<META http-equiv=Content-Type content="text/html; charset=GBK"> 
<TITLE>[email protected]</TITLE> 
</HEAD> 
<BODY> 
<% DefaultPieDataset data = new DefaultPieDataset(); 
data.setValue("高中以下",370); 
data.setValue("高中",1530); 
data.setValue("大专",5700); 
data.setValue("本科",8280);  
data.setValue("硕士",4420); 
data.setValue("博士",80);  PiePlot3D plot = new PiePlot3D(data);//3D饼图 
plot.setURLGenerator(new StandardPieURLGenerator("barview.jsp"));//设定链接 
JFreeChart chart = new JFreeChart("",JFreeChart.DEFAULT_TITLE_FONT, plot, true); 
chart.setBackgroundPaint(java.awt.Color.white);//可选，设置图片背景色 
chart.setTitle("程序员学历情况调查表");//可选，设置图片标题 
StandardEntityCollection sec = new StandardEntityCollection(); 
ChartRenderingInfo info = new ChartRenderingInfo(sec); 
PrintWriter w = new PrintWriter(out);//输出MAP信息 
//500是图片长度，300是图片高度 
String filename = ServletUtilities.saveChartAsPNG(chart, 500, 300, info, session); 
ChartUtilities.writeImageMap(w, "map0", info, false); String graphURL = request.getContextPath() + "/servlet/DisplayChart?filename=" + filename;  %> <P ALIGN="CENTER"> 
<img src="<%= graphURL %>" width=500 height=300 border=0 usemap="#map0"> 
</P> 
</BODY> 
</HTML>  
看了网上一个例子，然后生成了图片但是查看源代码时却看的连接找不到
<map id="map0" name="map0">
<area shape="poly" coords="247,52,250,52,250,138,250,138" href="barview.jsp%3Fcategory%3D%25E5%258D%259A%25E5%25A3%25AB%26amp%3BpieIndex%3D0" alt=""/>
<area shape="poly" coords="131,122,137,108,146,95,157,83,171,72,188,64,206,58,226,53,247,52,250,138,250,138" href="barview.jsp%3Fcategory%3D%25E7%25A1%2595%25E5%25A3%25AB%26amp%3BpieIndex%3D0" alt=""/>
<area shape="poly" coords="336,198,321,208,305,215,287,220,269,223,250,224,231,223,212,220,194,215,178,207,163,198,151,188,141,176,134,163,130,150,129,136,131,122,250,138,250,138" href="barview.jsp%3Fcategory%3D%25E6%259C%25AC%25E7%25A7%2591%26amp%3BpieIndex%3D0" alt=""/>
<area shape="poly" coords="316,66,336,78,352,93,363,110,369,129,369,148,363,166,352,183,336,198,250,138,250,138" href="barview.jsp%3Fcategory%3D%25E5%25A4%25A7%25E4%25B8%2593%26amp%3BpieIndex%3D0" alt=""/>
<area shape="poly" coords="263,52,291,57,316,66,250,138,250,138" href="barview.jsp%3Fcategory%3D%25E9%25AB%2598%25E4%25B8%25AD%26amp%3BpieIndex%3D0" alt=""/>
<area shape="poly" coords="250,52,263,52,250,138,250,138" href="barview.jsp%3Fcategory%3D%25E9%25AB%2598%25E4%25B8%25AD%25E4%25BB%25A5%25E4%25B8%258B%26amp%3BpieIndex%3D0" alt=""/>
</map>
被这个问题困扰了好久，请问这是什么原因？