java dispatcher.forward 抛出空异常答案

【问题标题】：java dispatcher.forward throw null exceptionjava dispatcher.forward 抛出空异常
【发布时间】：2013-02-15 03:36:29
【问题描述】：

我收到以下错误

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: java.lang.NullPointerException
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:548)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:471)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    ahp.CompareCriterionSlider.doGet(CompareCriterionSlider.java:35)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
root cause

java.lang.NullPointerException
    org.apache.jsp.CompareCriterionSlider_jsp._jspService(CompareCriterionSlider_jsp.java:91)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    ahp.CompareCriterionSlider.doGet(CompareCriterionSlider.java:35)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

专线：dispatcher.forward(request, response);

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession(true);
        session.setAttribute("criterions", CriterionRecommander.values() );
        RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/CompareCriterionSlider.jsp");
        dispatcher.forward(request, response);
    }

我在目录WebContent/ 中有CompareCriterionSlider.jsp

我试图设置断点来调试它，但是 eclipse(Version: Indigo Service Release 2) 给了我：Source not found.

谁投了我的票，愿意给出一个理由吗？

【问题讨论】：

标签： java eclipse jsp servlets requestdispatcher

【解决方案1】：

您的 JSP 抛出了一个空指针异常，您需要在 JSP 中找到导致该异常的确切代码行。
一种方法是简单地打开 jsp 的已编译 java 文件，即 CompareCriterionSlider_jsp.java:91，然后将其映射到 JSP 中的行。
一旦你这样做了，鉴于它是一个空指针，它应该很容易找出错误。

【讨论】：