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From "Giesen Giesen" <gies...@gmail.com>
Subject Re: NullPointerException in org.apache.log4j.NDC.get
Date Mon, 10 Jul 2006 19:58:39 GMT
I'm using 1.2.11, but in my Internet searching, I've seen someone else
getting the exact same error in 1.2.13 (google: NullPointerException
org.apache.log4j.NDC.get). I will upgrade my app.

Why would Thread.getCurrentThread() return null? Shouldn't that always
return a non-null value?

Thanks for the response and suggestions! I'm hoping that it will
happenly rarely enough to be overlooked until someone else identifies
the issue and develops a good patch. Or until 1.3 is officially

On 7/10/06, Curt Arnold <carnold@apache.org> wrote:
> On Jul 10, 2006, at 9:30 AM, Giesen Giesen wrote:
> > I sporadically get the following error when my JSF app starts up.
> > Anyone know what I can do? Would the 1.3 alpha version help? (I hate
> > to use prerelease software)
> >
> > Exception sending context initialized event to listener instance of
> > class com.sun.faces.config.ConfigureListener
> > java.lang.NullPointerException
> >       at org.apache.log4j.NDC.get(NDC.java:209)
> >       at org.apache.log4j.spi.LoggingEvent.getNDC(LoggingEvent.java:238)
> >       at org.apache.log4j.helpers.PatternParser
> > $BasicPatternConverter.convert(PatternParser.java:401)
> >       at org.apache.log4j.helpers.PatternConverter.format
> > (PatternConverter.java:64)
> >       at org.apache.log4j.PatternLayout.format(PatternLayout.java:503)
> >       at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:301)
> >
> You didn't mention what version of log4j 1.2.x you were using, so it
> isn't easy to match line numbers with particular statements.  In the
> latest log4j 1.2.x source, NDC.java:209 is:
>      Stack s = (Stack) ht.get(Thread.currentThread());
> The two mechanisms that I would see for a NullPointerException would
> be if either ht or Thread.getCurrentThread() are null.  I do not see
> a mechanism for either of those to happen.  Unfortunately, "ht" is
> neither private or final so there is a possibility that some other
> class modifies the value.  That appears to be unanticipated as ht ==
> null is never checked in any of the other accesses of the variable.
> I assume that in your layout, you have a layout specification like: %X
> {FOOBAR} that could be removed to eliminate going down evaluating the
> NDC which might allow you to avoid the bug.
> log4j 1.3.x appears to use a substantially different implementation.
> So it might not have this issue, but I would not recommend changing
> based on this issue until it is understood.
> Please let us know what version of log4j you are running.  If not the
> current log4j 1.2.x, does the problem appear with latest log4j
> 1.2.x?  If it does, if you could figure out whether
> Thread.currentThread() is returning null or ht is null.
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