请求调度程序空指针异常

【问题标题】：Requestdispatcher Nullpointer Exception请求调度程序空指针异常
【发布时间】：2023-03-08 18:38:01
【问题描述】：

我有以下 Servlet 代码：

@WebServlet("/Login")
public class Login extends HttpServlet {
private static final long serialVersionUID = 1L;
public String lang = "";   
/**
 * @see HttpServlet#HttpServlet()
 */
public Login() {
    super();
    // TODO Auto-generated constructor stub
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    String lcLog = request.getParameter("LogType").toUpperCase();
    switch(lcLog)
    {
        case "LOGIN":
            try {
                boolean llErfolg = doLogin(request.getParameter("user").toUpperCase(),request.getParameter("pw"));
                if(llErfolg==true)
                {
                    System.out.println("Login");
                    HttpSession session = request.getSession();
                    session.setAttribute("username", request.getParameter("user").toUpperCase());
                    session.setAttribute("Language", lang);
                    request.getRequestDispatcher("/WEB-INF/jsp/view/Kacheln_Test.jsp").forward(request, response);
                }
                else
                {
                    System.out.println("Login Failed");
                    request.setAttribute("LogInFailed", true);
                    request.getRequestDispatcher("/WEB-INF/jsp/view/Startseite.jsp").forward(request, response);
                }
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            break;
        case "LOGOUT":
            System.out.println("Logout");
            HttpSession session = request.getSession();
            session.invalidate();
            request.getRequestDispatcher("/WEB-INF/jsp/view/Startseite.jsp").forward(request, response);
            break;
        default:
            System.out.println("Warum?");
            break;
    }
}

到目前为止一切正常，但最近每当我遇到“LogOut”的情况时，我都会在 Dispatcher 收到 Nullpointer 异常，我完全不知道为什么，因为它在几天前就工作了。

我有关注 Kacheln_Test.jsp 文件，可能是问题的根源，因为当我点击“Kunden”时会发生同样的错误

<c:url var="post_url2" value="/Login" />
<form id="LogOut" method="POST" action="${post_url2}" name="LogOut">
    <input type="hidden" id="LogType" name="LogType" value = "" />
    <fmt:message key="Kacheln.Label.Angemeldetals"/>&emsp; <%=session.getAttribute("username") %>,
    <a href="javascript:{}" onclick="ausloggen_setzen('LogOut');"><fmt:message key="Kacheln.Label.LogOut"/> </a>
</form>

同样的错误

<div class="image-container">
    <div class="frame">
       <input class="live-slide"  type ="image" src="Images/Kunden.png" onClick="return setValue('Mail')" />
    </div>
    <div class="image-overlay" onclick="return setValue('Kunden')">
        <fmt:message key="Kacheln.Button.Kunden"/>
    </div>
</div>

这是调用的函数

<script>
    function ausloggen_setzen(lcTest)
    {
        document.getElementById('LogType').value = lcTest;
        document.getElementById('LogOut').submit();
        return true;
    }
    function setValue(lcArt)
    {
        document.getElementById("OF").value = lcArt;
        document.getElementById("OFform").submit();
        return true;
    }
</script>

希望有人能帮忙，我认为这只是一件小事，但我不知道原因

错误堆栈跟踪：

Jul 12, 2017 8:46:22 AM org.apache.catalina.core.StandardWrapperValve    
invoke
SCHWERWIEGEND: Servlet.service() for servlet [Login] in context with path
 [/Tuev_Test] threw exception [org.apache.jasper.JasperException:   
java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at     org.apache.jsp.WEB_002dINF.jsp.view.Menu_jsp._jspService(Menu_jsp.java:251)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:716)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:584)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:523)
at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:885)
at org.apache.jsp.WEB_002dINF.jsp.view.Startseite_jsp._jspService(Startseite_jsp.java:136)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:716)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:466)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:391)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:318)
at Login.doPost(Login.java:73)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:616)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1533)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1489)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

您好，

凯文

【问题讨论】：

  • 发布你的 Nullpointer 异常堆栈跟踪
  • 我添加了堆栈跟踪
  • 你的 Startseite.jsp 在哪里，它可能有问题包含
  • 为什么会有问题呢？在程序开始时，jsp 被调用并正常打开，但是当我点击 Kacheln_Test.jsp 上的“Ausloggen”时，就会发生错误，那里与网站开始时应该有什么不同？
  • 顺便说一句，你为什么要调用 session.invalidate();之前呢？可以去掉吗？

标签： jsp servlets request requestdispatcher


【解决方案1】：

我发现了我的两个问题，一步一步仔细检查代码，我看到在“Kunden”和“Startseite”两个包含的jsp中都有一个request.getAttribute()。在我的两种情况下，都存在空指针异常，我忘记在调用 jsp 之前设置属性。

但因为一开始只是有一个 Nullpointerexception，我变得不确定，所以我完全监督了明显的原因

感谢您的回答，并为我的盲目和愚蠢感到抱歉:(

您好，

凯文

【讨论】：

    猜你喜欢
    • 2015-06-16
    • 2017-06-13
    • 1970-01-01
    • 1970-01-01
    • 1970-01-01
    • 2015-07-12
    相关资源
    最近更新 更多
    热门标签
    Java Python linux javascript Mysql C# Docker 算法 前端 SpringBoot Redis Vue spring 设计模式 .net core .net kubernetes c++ 数据库 数据结构 大数据 js 机器学习 微服务 Android Go 程序员 面试 JVM ASP.net core 云原生 人工智能 后端 PHP git CSS golang k8s Nginx Django mybatis 深度学习 多线程 React 架构 devops 爬虫 云计算 Spring Boot LeetCode