Question

我无法使我的代码正常工作，我得到的唯一线索是关于未经检查的演员的警告，但在我看来，我不能更精确......

我尝试将@SuppressWarnings (value="unchecked")放在<% %>的代码上方，但它没有用...

以下是错误日志：

juin 22, 2016 4:25:34 AM org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: Servlet.service() for servlet [GroupeEleve] in context with path [/GAPP2] threw exception [
An exception occurred processing JSP page /WEB-INF/view/profilEtudiant.jsp at line 668

665:     <tr>
666:     <% 
667:         Users U = (Users)session.getAttribute("user");
668:         Set<Absences> A=(Set<Absences>)U.getAbsenceses();
669          List<Absences> B = new ArrayList<Absences>(A);
670:         for(int i=0;i<B.size();i++){%>
671:             <td><%out.print(B.get(i).getDate()) ;%></td>


Stacktrace:] with root cause
java.lang.NullPointerException
    at org.apache.jsp.WEB_002dINF.view.profilEtudiant_jsp._jspService(profilEtudiant_jsp.java:817)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:439)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:747)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:485)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:410)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:337)
    at com.isep.controlleurs.GroupeEleve.doGet(GroupeEleve.java:46)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:436)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    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)

Answer 1

可能是你的会话没有User属性。请检查你的会话user.if用户不是null，那么它可能是U.getAbsenceses（）返回null而Set A将得到null值。所以当你从A到B赋值，当你调用B.get（i）.getDate（）时会导致空指针异常。

org.apache.jsp.WEB_002dINF.view.profilEtudiant_jsp._jspService中的java.lang.NullPointerException

1 个答案: