Tom Davis wrote:

> Hi All.
>
> I'm getting some intermittent exceptions from Tomcat with which I
> would appreciate some assistance. I get an IllegalStateException from
> Tomcat. This is not a unique error, though it looks like the
> circumstances causing it are. We have a complex application, with
> multiple servlets and many JSPs. The specific type of
> IllegalStateException is a TODO, and it usually occurs when we call
> sendError() on the HttpServletResponse object. I know this sounds
> like the typical coding error, but we have checked very carefully and
> haven't found it. We have looked through many of the posts on other
> occurrences of this exception, including the Tomcat documentation that
> describes its common causes. We've checked those method calls (e.g.,
> getWriter() or getOutputStream() followed by a sendError() or similar
> call), and can't see any logical errors in the flow of code.
>
> The exception only occurs when one specific servlet is active. This
> servlet is a custom proxy, and behaves as an Http client to other
> servers. Interestingly, the exception doesn't get thrown from the
> proxy servlet, it actually pops up in several of the other servlets.
> We put in lots of debug statements and found that sometimes
> (approximately 20% of the time) the 'isCommitted()' method on the
> HttpServletResponse object indicates that the response is already
> committed *upon entry* to the proxy servlet! But even when
> isCommitted() indicates true, it only occasionally leads to the
> exception occurring in the other servlets.

Sounds like a synchronization/multi-threading issue to me. Did you
check for that stuff in your code review?


> It seems that Tomcat is getting confused at the core by the proxy
> servlet - why else would the response appear to already be committed
> upon entry to our servlet. Possibly this is due to the web client
> nature of the proxy servlet? Or maybe a subtle bug somewhere in the
> proxy code that overwrites something internally in Tomcat?
>
> We can avoid the IllegalStateException by not calling sendError if the
> response is committed, but either way the application doesn't behave
> properly.
> Environment: We get the same problem on in different environments,
> which strongly indicates it is specific to the Tomcat 5.5.X line:
> OS: Windows 2000, Windows XP, AIX
> JVM: 1.4.2_12-b03 on Win32, J2RE 1.4.2 IBM AIX build ca142-20060824
> (SR6)
> Tomcat: 5.5.7 and 5.5.20
>
> The Tomcat FAQ lists *the most common* reasons for getting an
> IllegalStateException. I think we need to go to the next level. Does
> anyone know the more subtle reasons for getting this?
>
> Thanks,
> Tom Davis
>
>
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>
>



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