Java Servlet/Jsp/CanvasJs 从 Servlet 获取数据到 Jsp

Question

您好，我是 Web 开发的新手，Java，感谢您的提前帮助。

我正在尝试将预定义数据从 servlet 获取到 jsp 中的 canvasjs 图形中。

我使用 Eclipse Oxygen 和 TomCat 8.5

简而言之，我的代码如下所示：

ChartValues.java 只是有变量实例化，所以我认为不值得展示

jsp 文件:

<%@page import="saagnik.ChartValues"%>
<%@page import="java.util.ArrayList"%>
<%@page session="true" %>

    <%@ page language="java" contentType="text/html; charset=UTF-8"
        pageEncoding="UTF-8"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <script type="text/javascript"src="https://canvasjs.com/assets/script/canvasjs.min.js"></script>

        <script type="text/javascript">

        window.onload = function() {

        var datapoints=[];

        var chart = new CanvasJS.Chart("chartContainer1",{
           title:{
                text: "Anzahl der Requests"
            },
            data: [{
                    type: "splineArea",
                    name: "Anzahl",
                    dataPoints: datapoints
                }]
        });

        String test=(String)session.getAttribute("test1");

        datapoints.push({x: new Date(2015, 03, 10), y: 10});

        chart.render();
    </script>
    </header>
    <body>
         <div id="chartContainer1"></div>
    </body>
    </html>

当我评论会话行时，程序工作正常，但当它被包含时，图表将无法构建。

Servlet 文件：

    package saagnik; 
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;

    @WebServlet("/ChartServlet")
    public class ChartServlet extends HttpServlet {
        private static final long serialVersionUID = 1L;
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
                doPost(request,response);
        }
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

            int test =10;
            HttpSession session=request.getSession(true);
            session.setAttribute("test1", test);

            response.sendRedirect("CharttestCanvas3.jsp");

        }
}

也尝试在 doGet 中使用请求，例如：

ChartValues[] articles =
                new ChartValues[] {new ChartValues(39500,1.5,0.5,"16/01/09/2019"), new ChartValues(49500,1.5,0.5,"17/01/09/2019")};
        request.setAttribute("articles", articles);

        RequestDispatcher dispatcher = request.getRequestDispatcher("CharttestCanvas3.jsp");
        dispatcher.forward(request, response);

并在Jsp中与

ArrayList<ChartValues> chartvalue1 =  (ArrayList<ChartValues>)request.getAttribute("chartdata");

但我得到了相同的结果。

Answer 1

我的错误是认为 script 和 scriptlet 是相似的，并且当运行加载 jsp 文件时我可以看到完成的图形。当运行ning JSP 值为 null。我需要在脚本中使用 Javascript 并在 servlet 中使用运行图表才能使其正常工作。

将 servlet 传输从会话更改为请求。

servlet：

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        Integer value=15;
        request.setAttribute("value", value);
        request.getRequestDispatcher("CharttestCanvas3.jsp").forward(request, response);
        }

对于 JSP 我结合了脚本和小脚本来让它工作。

JSP:

    <%Integer value = (Integer)request.getAttribute("value");%>

    <script type="text/javascript">
    window.onload = function() {
    .
    .
    .
    var aa=+'<%=value%>';
    datapoints.push({x: new Date(2015, 03, 10), y: aa});
    chart.render();
    .
    .
    .
    </script>

小脚本中是来自请求的值。通过 scriptlet=value 值进入我的脚本，加号将 var 确定为 int。

Java Servlet/Jsp/CanvasJs 从 Servlet 获取数据到 Jsp

Java Servlet/Jsp/CanvasJs Getting Data from Servlet into Jsp

java

jsp

servlets

canvasjs