帶有servlet的JFREECHART

Question

我正在嘗試讓JFREECHART為圖表中的一些硬編碼數據創建png。 我完全沒有錯誤，我在創建部分中運行的程序也沒有，但我沒有得到png。

誰能看到問題出在哪里？

我的servlet

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String action = request.getParameter("Action");
    if(action.equals("Home"))
        getServletContext().getRequestDispatcher(home).forward(request, response);

    else{
        session = request.getSession(true);
        user = (User) session.getAttribute("User");
        eventList = rh.getEventList(user);
        request.setAttribute("EventList", eventList);
        getServletContext().getRequestDispatcher(result).forward(request, response);

        DefaultCategoryDataset dataset = new DefaultCategoryDataset();
        dataset.setValue(30, "Girls","SCIENCE CLASS");
        dataset.setValue(30,  "Boys","SCIENCE CLASS");
        dataset.setValue(10,  "Girls","ECONOMICS CLASS");
        dataset.setValue(50, "Boys","ECONOMICS CLASS");
        dataset.setValue(5, "Girls","LANGUAGE CLASS");
        dataset.setValue(55, "Boys","LANGUAGE CLASS");

        JFreeChart chart = ChartFactory.createLineChart(
                "Comparison between Girls and Boys in Science," + "Economics and Language classes",
                "Students Comparisons", "No of Students",
                dataset,
                PlotOrientation.VERTICAL,
                true,
                true,
                false);


            try {

                final ChartRenderingInfo info = new ChartRenderingInfo(new StandardEntityCollection());
                final File file1 = new File(getServletContext().getRealPath(".") + "/images/lineChart.png");

                ChartUtilities.saveChartAsPNG(file1, chart, 600, 400, info);
            } catch (Exception e) {
                System.out.println(e);

            }
    }
}

和我的jsp

                <div>
                <img src="path/images/lineChart.png"
                     width="600" height="400" border="0" usemap="#chart" />
            </div>

Answer 1

為此，必須在呈現JSP之前調用Servlet。 但是，您采用的方法還有其他缺陷。

我建議不要將生成的圖表寫到文件中，而應將其直接流到Servlet的響應流中：

http://www.jfree.org/jfreechart/api/javadoc/org/jfree/chart/ChartUtilities.html#writeChartAsPNG-java.io.OutputStream-org.jfree.chart.JFreeChart-int-int-

 try {
    final ChartRenderingInfo info = new ChartRenderingInfo(new StandardEntityCollection());
    ChartUtilities.writeChartAsPNG(response, chart, 600, 400, info);
} catch (Exception e) {
    System.out.println(e);
}

然后，只需將<img/>標記指向Servlet：

<div>
    <img src="pathToMyServlet" width="600" height="400" border="0" usemap="#chart" />
 </div>