JFreeChart图片不能显示

代码如下：<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ page import="org.jfree.data.category.*" %>
<%@ page import="org.jfree.chart.*" %>
<%@ page import="org.jfree.chart.plot.*" %>
<%@ page import="org.jfree.chart.servlet.*" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<%
response.setContentType("image/jpeg");
response.setContentType("text/html");
DefaultCategoryDataset dataset=new DefaultCategoryDataset();
dataset.addValue(610,"广州","猪肉");
dataset.addValue(540,"广州","牛肉");
dataset.addValue(320,"广州","羊肉");
dataset.addValue(370,"广州","鸡肉");
dataset.addValue(130,"广州","鱼肉");

JFreeChart chart=ChartFactory.createBarChart3D("BiangJi","销量","肉类",dataset,PlotOrientation.VERTICAL,false,false,false);
String fileName=ServletUtilities.saveChartAsJPEG(chart,500,300,session);
String serverName=request.getServerName();
String port=String.valueOf(request.getServerPort());

out.print(fileName+"---fileName<br/>");
out.print(serverName+"---serverName<br/>");
out.print(port+"---serverName<br/>");
String url="http://"+serverName+":"+port+request.getContextPath()+"/servlet/DisplayChart?fileName="+fileName;
out.print("url:"+url);
 %><img src="<%=url %>" width="500" height="300" usemap="#<%=fileName %>"></body>
</html>web.xml中配置如下：
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" 
xmlns="http://java.sun.com/xml/ns/j2ee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet>
     <servlet-name>DisplayChart</servlet-name>
     <servlet-class>org.jfree.chart.servlet.DisplayChart</servlet-class>
</servlet><servlet-mapping>
      <servlet-name>DisplayChart</servlet-name>
      <url-pattern>/servlet/DisplayChart</url-pattern>
</servlet-mapping></web-app>图片为一个叉叉
不知道为什么