今天利用JFreeChart结合DWR ReverseAjax实现服务器数据“推”到客户端；在客户端用JFreeChart默认的org.jfree.chart.servlet.DisplayChart
显示图片，会出现不同的客户端不能显示图片；查看DisplayChart源码
public void service(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession();
String filename = request.getParameter("filename");
if (filename == null) {
throw new ServletException("Parameter 'filename' must be supplied");
}
// Replace ".." with ""
// This is to prevent access to the rest of the file system
filename = ServletUtilities.searchReplace(filename, "..", "");
// Check the file exists
File file = new File(System.getProperty("java.io.tmpdir"), filename);
if (!file.exists()) {
throw new ServletException("File '" + file.getAbsolutePath()
+ "' does not exist");
}
// Check that the graph being served was created by the current user
// or that it begins with "public"
boolean isChartInUserList = false;
ChartDeleter chartDeleter = (ChartDeleter) session.getAttribute(
"JFreeChart_Deleter");
if (chartDeleter != null) {
isChartInUserList = chartDeleter.isChartAvailable(filename);
}
boolean isChartPublic = false;
if (filename.length() >= 6) {
if (filename.substring(0, 6).equals("public")) {
isChartPublic = true;
}
}
boolean isOneTimeChart = false;
if (filename.startsWith(ServletUtilities.getTempOneTimeFilePrefix())) {
isOneTimeChart = true;
}
if (isChartInUserList || isChartPublic || isOneTimeChart) {
// Serve it up
ServletUtilities.sendTempFile(file, response);
if (isOneTimeChart) {
file.delete();
}
}
else {
throw new ServletException("Chart image not found");
}
return;
}
其中无法显示的图片的原因跟
isChartInUserList || isChartPublic || isOneTimeChart 有关；其中isChartInUserList是为同一session，因服务器推是同时推向多客户端，这个isChartInUserList为false是没法改变；isOneTimeChart是在创建chart的时候，如果session为null则会记录该chart为one-time use，显示一次后会被删除；因此想从isChartPublic入手了；但是JFreeChart API并没发现提供如何产生public+filename的chart；因此重写DisplayChart默认为public，这样所有的客户端都可以显示。
posted on 2008-09-09 17:26
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