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，但最近每当我得到这样的情况＆＃34; LogOut＆＃34;，我在Dispatcher得到一个Nullpointer异常，我完全不知道为什么，因为它在几天前工作了。
我有以下Kacheln_Test.jsp文件，也许有问题的根源，因为当我点击＆＃34; Kunden＆＃34;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"/>  <%=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>
这是名为
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>
错误Stacktrace：
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)
问候，
凯文
答案 0 :(得分：0)
我已经找到了我的两个问题，一步一步地仔细查看代码，我看到在包含jsp的情况下，我在“Kunden”和“Startseite”都有一个request.getAttribute（）。在我的两种情况下，如果存在nullpointerexception，我忘记在调用jsp之前设置属性。
但是因为刚开始只有一个Nullpointerexception，我变得不确定，所以我完全监督了明显的原因
感谢你的回答，对不起我的失明和愚蠢:(
问候，
凯文