Spring 3 -- NullPointerException in controller calling JSP

Question

I am getting the following error message from my Spring controller method when it attempts to pass control to a JSP.

java.lang.NullPointerException
    at org.apache.jsp.WEB_002dINF.pages.PollPage_jsp._jspService(PollPage_jsp.java:202)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:684)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:471)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:402)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:262)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1265)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1016)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:965)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:859)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:883)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:781)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:395)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Here is the relevant part of my controller.

@RequestMapping(value = "/polls") 
public String polls(Model model, HttpServletRequest request) {
    // processing that's not relevant to the problem

    return "PollPage";
}

Here is my JSP code.

    <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1"%>
    <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
    <%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>
    <%@ taglib prefix="myTag1" uri="poll1"%>
    <%@ taglib prefix="myTag2" uri="poll2"%>
    <%@ taglib prefix="myTag3" uri="poll3"%>
    <c:set var="foundCookiePoll1" value="false" scope="page" />
    <c:set var="foundCookiePoll2" value="false" scope="page" />
    <c:set var="foundCookiePoll3" value="false" scope="page" />
    <c:set var="poll1Yes" value="0" scope="page" />
    <c:set var="poll1No" value="0" scope="page" />
    <c:set var="poll2Job" value="0" scope="page" />
    <c:set var="poll2School" value="0" scope="page" />
    <c:set var="poll2Married" value="0" scope="page" />
    <c:set var="poll2Crazy" value="0" scope="page" />
    <c:set var="poll3zero" value="0" scope="page" />
    <c:set var="poll3one" value="0" scope="page" />
    <c:set var="poll3two" value="0" scope="page" />
    <c:set var="poll3three" value="0" scope="page" />
    <c:set var="poll3morethanthree" value="0" scope="page" />
    <!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=ISO-8859-1">
    <title>Poll Page</title>
    <style type="text/css">
    p {
        text-align: justify;
    }
    </style>
    </head>
    <body>
        <%
            Cookie[] cookies = request.getCookies();
            if (cookies != null) {
                for (int i = 0; i < cookies.length; i++) {
                    if (cookies[i].getName().equals("poll1")) {
                        %> <c:set var="foundCookiePoll1" value="true" /> <%
                    }

                    if (cookies[i].getName().equals("poll2")) {
                        %> <c:set var="foundCookiePoll2" value="true" /> <%
                    }

                    if (cookies[i].getName().equals("poll3")) { 
                        %> <c:set var="foundCookiePoll3" value="true" /> <%
                    }
                }
            }
            int poll1Yes = (Integer) request.getAttribute("poll1Yes");
            int poll1No = (Integer) request.getAttribute("poll1No");
            int poll2Job = (Integer) request.getAttribute("poll2Job");
            int poll2School = (Integer) request.getAttribute("poll2School");
            int poll2Married = (Integer) request.getAttribute("poll2Married");
            int poll2Crazy = (Integer) request.getAttribute("poll2Crazy");
            int poll3zero = (Integer) request.getAttribute("poll3zero");
            int poll3one = (Integer) request.getAttribute("poll3one");
            int poll3two = (Integer) request.getAttribute("poll3two");
            int poll3three = (Integer) request.getAttribute("poll3three");
            int poll3morethanthree = (Integer) request.getAttribute("poll3morethanthree");

         %>
        <center>
            <h1>Granada High School Class of 1986 Poll Page</h1>
        </center>
<!-- main content of page -->
    </body>
    </html>

When I step through the controller code in Eclipse, I get the following message:

The source attachment does not contain the source for the file InvocationHandlerMethod.class

This happens when I get another message saying this:

NativeMethodAccessorImpl.invoke(Object, Object[] line: not available

Can anyone shed some light on this? I'm thinking I might be missing a jar file.

Answer 1

Thanks to Nice Developer for the solution to this problem. I have solved the problem in my JSP by checking for null values like this.

Integer poll1Yes = new Integer(0);

if (request.getAttribute("poll1Yes") != null) {
    poll1Yes = (Integer) request.getAttribute("poll1Yes");
}