java dispatcher.forward抛出null异常

Question

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)

对于这一行： 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/有CompareCriterionSlider.jsp

我试图设置断点来对其进行调试，但是eclipse（版本：Indigo Service Release 2）给了我： Source not found.

谁拒绝我投票给我理由？

Answer 1

您的JSP抛出了一个空指针异常，您需要在导致它的JSP中找到确切的代码行。
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。
一旦这样做，给定它为空指针，就可以很容易地确定错误。