Tomcat 4.1.27:NullPointerException in getAttribute CoyoteRequestFacade under moderate server load

[Markus Mayer <m....@generali.at>]

Hi all,
we are using tomcat 4.1.27 as a servlet container (no jsp's). we used to 
have all our code in a large servlet which used to be working fine. in 
order to increase our flexibility we refactored some of our code into 
several servlet filters which we plugged before the main servlet. this 
works fine too when the machine is utilised with small loads only. as soon 
as we ramp up machine utilisation in our production environment however we 
start to get NullPointerExceptions in CoyoteRequestFacade's getAttribute 
method (I enclose an example stacktrace below). When we had all our code 
in our servlet we never experienced such problems. Is this a known issue 
or does anyone on the list has any tips/infos on how to properly implement 
filters in order to prevent such effects from happening?

Any help appreciated.

Thanks,
Markus

java.lang.NullPointerException
        at 
org.apache.coyote.tomcat4.CoyoteRequestFacade.getAttribute(CoyoteRequestFacade.java:141)
        at 
com.generali.vp.tomcat.filters.AbstractFilter.doFilter(AbstractFilter.java:89)
        at 
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
        at 
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
        at 
com.generali.vp.tomcat.filters.AbstractFilter.doFilter(AbstractFilter.java:85)
        at 
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
        at 
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
        at 
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
        at 
org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
        at 
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
        at 
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
        at 
org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
        at 
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
        at 
org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
        at 
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
        at 
org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
        at 
org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
        at 
org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
        at 
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
        at 
org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
        at 
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
        at 
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
        at 
org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
        at 
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
        at 
org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
        at 
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:601)
        at 
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:392)
        at 
org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:565)
        at 
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
        at java.lang.Thread.run(Thread.java:534)