public DisplayChart() 
{
        super();
}

Default constructor.

 public  void init() throws ServletException 
{
        return;
}

Init method.

 public  void service(HttpServletRequest request,
    HttpServletResponse response) throws IOException, ServletException 
{
        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;
}

Service method.