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From "A. Rothman" <>
Subject Re: Occasional NoClassDefFoundError, but disappears after couple of restarts
Date Mon, 03 Aug 2009 10:00:19 GMT
A couple months ago I had a slightly different setting but with the same 
strange result - NoClassDefFoundErrors which occurred on a particular 
jsp page in my app, but only if it was the first jsp accessed following 
a restart (and remained in the error state until the next restart). If 
it was not the first jsp accessed, then everything came up fine (with 
nothing in the configuration or app changing in between). I also figured 
it's some classloader bug in Tomcat, not entirely a race condition 
(since it did happen consistently), but something that manifests itself 
depending on the order of class loading.

I never did find out for sure what the problem was (maybe it's the sync 
issue Mark refers to below), but I stumbled upon a workaround, which I 
do not quite understand, which fixed this for good: I changed the order 
of the first two statements in the jsp, the first was one that accessed (a system class) and the second the session bean 
declaration (a custom app-specific class). Although the two statements 
were unrelated to each other and their order should not have made any 
difference, this solved the problem (switching them back did reintroduce 
the error, consistently). I still suspect the problem was with the order 
of classloading.

So, not sure if this will help, but in the off chance that your issue is 
related to the one I was experiencing, you might want to try fiddling 
with the order in which classes are accessed/loaded by Tomcat (either 
via their xml reference, or their actual content's first statements) and 
hopefully something will work. Yes, it sounds strange, but it worked for 
me in a reproducible manner.

Good luck :-)


Mark Thomas wrote:

> M4N - Arjan Tijms wrote:
>> I removed the obvious suspect, a duplicate postgresql driver that
>> appeared in both WEB-INF/lib  and [tomcat install dir]/lib.
>> Unfortunately this did not seem to help. Last night I needed to restart
>> the production server for a configuration change and I needed 22(!)
>> restarts for Tomcat to start up correctly.
>> It really seems that there's a race condition going on somehow. I mean,
>> if it was a structural problem then Tomcat would simply never start up,
>> wouldn't it?
> A reasonable conclusion.
>> The Jboss libraries are the Jboss client libraries and are needed to
>> consume EJBs from a remote Jboss AS instance. Maybe there are some
>> classes somewhere that conflict with those of Tomcat, but if that would
>> be true it's still hard to understand why starting up fails in
>> production but never on a local workstation.
> Does the production box have more cores than the dev box? If there was a
> race condition you would be more likely to see it with more cores.
>> Anyone has any idea?
> There was a sync issue in the webappclassloader fixed in 6.0.19.
> Although the symptoms were different, it might be worth trying 6.0.20.
> Mark
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