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From Curt Arnold <carn...@apache.org>
Subject Re: PatternLayout + MDC Problem
Date Wed, 08 Oct 2008 20:21:39 GMT

On Oct 8, 2008, at 2:41 PM, Stefan Borovac wrote:

> Hi All,
> I'am currently working on a simple service which connects the
> XMLSocketReceiver with a DBAppender.
> I'am using the latest SNAPSHOTs from either log4j, log4j-components,
> and log4j-receiver.
> To test the service, I connect a ConsoleAppender to a logger to track
> the transmitted packages. The ConsoleAppender is staffed with a
> PatternLayout having a ConversionPattern such that the MDC should be
> printed.
> But the instead of the MDC being printed I end up with a NPE. This is
> caused in the MDCPatternConverter which should be initialised with a
> key being used later to extract values from the MDC hash. But this key
> is null, causing the hash function to crash throwing a NPE.
> A similar setup should work in Chainsaw. Hence I assume there will  
> be a
> solution for something selfmade (or am I a bit to optimistic).
> Any help or guess is welcome. I honestly don't want to crawl through  
> the
> Chainsaw code.
> Cheers
>  Stefan

Likely you have a pattern like with a "%X" with no key name (that is  
not "%X{key}").  org.apache.log4j.EnhancedPatternConverter in the  
extras companion supports just a plain "%X" and will output all  
existing key-value pairs.  It does look like the  
org.apache.log4j.PatternLayout will NPE in that case which is not  
desirable and it would be good to enhance it to support an unqualified  

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