我正在尝试创建一个在线测验应用程序，并设置了所有我的java类来进行测验，并在控制台中测试它们以确保它们输出我需要的内容。
然而，当我访问我的C1Test.jsp页面时，应该生成一个测验，我得到了glassfish抛出的NullPointerException，在做了一些谷歌搜索之后，我仍然不确定为什么。
可以在下面找到堆栈跟踪，以及我的C1Test.jsp源代码。任何帮助都会非常感激，这是我计算机科学学位的最后一年项目，在修复之前我无法取得任何进展。
提前致谢。
Info: Closing WebApplicationContext for namespace 'dispatcher-servlet'startup date [Tue Nov 24 16:32:38 GMT 2015]; parent: Root WebApplicationContext
Info: WebModule[null] ServletContext.log():Closing Spring root WebApplicationContext
Info: Closing Root WebApplicationContext: startup date [Tue Nov 24 16:32:37 GMT 2015]; root of context hierarchy
Warning: StandardWrapperValve[jsp]: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.C1Test_jsp._jspService(C1Test_jsp.java:101)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:411)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:473)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:377)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:415)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:282)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:201)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:175)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:561)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:565)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:545)
at java.lang.Thread.run(Thread.java:745)
C1Test.jsp源代码：
<%--
Document : C1 Test
Created on : Nov 5, 2015, 6:47:35 PM
Author : Joe Perkins
--%>
<%@ page language="java" import="Dissertation.*" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>C1 Test</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
</head>
<body>
<nav class="navbar navbar-inverse">
<div class="container-fluid">
<div class="navbar-header">
<a class="navbar-brand" href="HomePage.jsp">EduMath</a>
</div>
<div>
<ul class="nav navbar-nav">
<li><a href="Index.jsp">Home</a></li>
<li><a href="C1.jsp">C1 Revision</a></li>
<li><a href="C2.jsp">C2 Revision</a></li>
<li><a href="SkillsetDeveloper.jsp">Skillset Development</a></li>
<li><a href="About.jsp"> About</a></li>
</ul>
</div>
</div>
</nav>
<div class="container">
<div class="jumbotron">
<h1>C1 Revision Test</h1>
</div>
<div class="container">
<%
// Retrieve the current quiz question
int currQuestion = ((Exam)request.getSession().getAttribute("currentTest")).getCurrentQuestion();
System.out.println("Question No. " + currQuestion);
%>
Current Question ${sessionScope.quest.questionNo+1} / 10
<span>${sessionScope.quest.question}</span><br/><br/>
<form class ="form-horizontal" action="test" method="post">
<c:forEach var="choice" items="q${sessionScope.quest.questionOptions}" varStatus = "counter">
<input type="radio" name="answer" value="${counter.count}" >${choice} <br/>
</c:forEach> <br />
<%
if(currQuestion > 0)
{
%>
<input type="submit" name="action" value="previous"/>
<% } %>
<%
if(currQuestion < 19)
{
%>
<input type="submit" name="action" value ="next"/>
<% } %>
<input type="submit" name="action" value="Finish Exam"/>
</form>
</form>
</div>
</div>
</body>
</html>
编辑：与标记为可能重复的问题不同，我理解NullPointerException的基础，但更多的是寻找关于如何根据堆栈跟踪识别NullPointer来源的一般建议，以及如何最好地设置会话属性。
答案 0 :(得分：0)
确保在对其内容执行任何操作之前设置了会话属性currentTest。