今天利用JFreeChart結合DWR ReverseAjax實現服務器數據“推”到客戶端；在客戶端用JFreeChart默認的org.jfree.chart.servlet.DisplayChart
顯示圖片，會出現不同的客戶端不能顯示圖片；查看DisplayChart源碼
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;
}
其中無法顯示的圖片的原因跟
isChartInUserList || isChartPublic || isOneTimeChart 有關；其中isChartInUserList是為同一session，因服務器推是同時推向多客戶端，這個isChartInUserList為false是沒法改變；isOneTimeChart是在創建chart的時候，如果session為null則會記錄該chart為one-time use，顯示一次后會被刪除；因此想從isChartPublic入手了；但是JFreeChart API并沒發現提供如何產生public+filename的chart；因此重寫DisplayChart默認為public，這樣所有的客戶端都可以顯示。
posted on 2008-09-09 17:26
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