在同一JSP网页上包含JfreeChart图形和计算结果

Question

我有一个servlet，它根据用户提交的表单数据执行一些计算。

我想在图表中绘制输入值以及在同一网页上显示为文本的计算结果。

我可以使用JFreeChart创建图形，但如果我使用OutputStream，它会覆盖表单页面。如果我存储图像并尝试在JSP中链接URL，则不会显示图表。有什么想法可以实现吗？

这是我的servlet，它读取从浏览器提交的不同权重参数，并使用OutputStream创建图表：

@WebServlet(name = "resultServlet", urlPatterns = {"/results"})
public class resultServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    doPost(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    try { 
     List<Double> weightsList = new ArrayList<Double>();
     int listpos = 0;
     DefaultPieDataset myServletPieChart = new DefaultPieDataset();
         double w1 = Double.valueOf(request.getParameter("w1"));
         myServletPieChart.setValue("WEIGHTONE", w1);
         weightsList.add(listpos, w1); 
         listpos++;
         double w2 = Double.valueOf(request.getParameter("w2"));
         myServletPieChart.setValue("WEIGHTTWO", w2);
         weightsList.add(listpos, w2); 
         listpos++;
         double w3 = Double.valueOf(request.getParameter("w3"));
         myServletPieChart.setValue("WEIGHTTHREE", w3);
         weightsList.add(listpos, w3); 
         listpos++;
         double w4 = Double.valueOf(request.getParameter("w4"));
         myServletPieChart.setValue("WEIGHTFOUR", w4);
         weightsList.add(listpos, w4); 
         request.setAttribute("WeightSel", weightsList);  //list of selected weights
         request.setAttribute("WeightSum", weightSum(weightsList)); //sum of selected weights
         request.setAttribute("CalcResult", resultCalculator(weightsList)); //result of some calculations performed on selected weights
         // set piechart attributes
         JFreeChart inputWeightsPie = ChartFactory.createPieChart("Selected Weights",myServletPieChart,true,true,false);
         response.setContentType("image/png"); /* Set the HTTP Response Type */
         OutputStream out = response.getOutputStream();
         ChartUtilities.writeChartAsPNG(out, inputWeightsPie, 400, 300);/* Write the data to the output stream */
         //or alternatively:
         // ImageIO.write(inputWeightsPie.createBufferedImage(400, 300), "png", out);
         out.close();
        }

    } catch (NumberFormatException nfe) {
        request.setAttribute("errorMessage", "value must be a number!"); 
    }
    ServletContext ctx = this.getServletContext();
    RequestDispatcher dispatcher = ctx.getRequestDispatcher("/index.jsp");
    dispatcher.forward(request, response);
}

Answer 1

您当前的（主）servlet应该仅用于html内容
为图表创建单独的servlet（可以在其中使用writeChartAsPNG）
在JSP页面上，将其用作<img src="servChart?w1=100&w2=200">和您的参数。

更新
您也可以在同一个servlet中进行图表计算。将JFreeChart对象放入会话。在servChart?name=myChartservlet中，从会话中获取JFreeChart（按属性名称）并以字节形式输出。