遇到一个奇怪问题，请各位大侠帮帮忙

Question

HTTP 500-
The server encountered an internal error() that prevented it from fulfilling this request
java.lang.NullPointerException
     com.opensymphony.webwork.interceptor.FileUploadInterceptor.intercept.
     com.opensymphony.webwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java)
     com.opensymphony.webwork.DefaultActionProxy.execute(DefaultActionProxy.java)
     com.opensymphony.webwork.dispatcher.ServletDispatcher.servletAction
     com.opensymphony.webwork.dispatcher.ServletDispatcher.service
     javax.servlet.http.HttpServlet.service
     org.displaytab.filter.ResponseOverrideFilter.doFilter
     com.opensymphony.webwork.webwork.lifecycle.RequestLifecycleFilter.doFilter
The full stack trace of the root cause by avaliable in the Apache Tomcat 在web应用中，这个问题偶尔出现， 查了下web应用的客户端，发现他们的网络有丢包问题，不知道这个是不是原因 

Answer 1

FileUploadInterceptor文件上传，换个插件上传文件。

Answer 2

这个web应用是很多客户机在使用，只有一个客户机出现了这个问题，而且客户机都有固定IP

Answer 3

页面里面用到的属性，在formbean里面没有定义。检查一下

Answer 4

我当初也是怀疑4楼说的那种情况，但是这个web应用现在一直在跑着，别的客户没有反应这个问题，单单是这一个固定的客户出现了这个情况，应该不是formbean的问题吧

Answer 5

补充问题描述
java.lang.NullPointerException
at com.opensymphony.webwork.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:101)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:164)
at com.opensymphony.xwork.DefaultActionProxy.execute(DefaultActionProxy.java:116)
at com.opensymphony.webwork.dispatcher.ServletDispatcher.serviceAction(ServletDispatcher.java:280)
at com.opensymphony.webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:250)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.displaytag.filter.ResponseOverrideFilter.doFilter(ResponseOverrideFilter.java:125)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at com.opensymphony.webwork.lifecycle.RequestLifecycleFilter.doFilter(RequestLifecycleFilter.java:69)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:810)

Answer 6

NullPointerException
空指针啊
FileUploadInterceptor.java:的第十行的对象值是空的,
估计是你没给对象初始化或者你传了一个null值,检查这一行的对象的值是不是null.