Author: carnold
Date: Thu Jan 15 08:17:15 2009
New Revision: 734741
URL: http://svn.apache.org/viewvc?rev=734741&view=rev
Log:
Bug 43867: Update Tomcat NPE FAQ
Modified:
logging/log4j/trunk/src/site/fml/faq.fml
Modified: logging/log4j/trunk/src/site/fml/faq.fml
URL:
http://svn.apache.org/viewvc/logging/log4j/trunk/src/site/fml/faq.fml?rev=734741&r1=734740&r2=734741&view=diff
==============================================================================
--- logging/log4j/trunk/src/site/fml/faq.fml (original)
+++ logging/log4j/trunk/src/site/fml/faq.fml Thu Jan 15 08:17:15 2009
@@ -789,27 +789,23 @@
when shutting down or restarting under Tomcat or during a
shutdown
hook?</question>
<answer><p>Tomcat will, by default,
- clear all static members when unloading classes.
- Unfortunately, under certain circumstances
- another class may attempt to call log4j after log4j
- has had its private member variables cleared, resulting in either
- a NullPointerException (log4j 1.2.14 or earlier) or a console
- message (log4j 1.2.15 and later). The same type of issue
- has been reported during various shutdown hooks (see bug
- <a
href="http://issues.apache.org/bugzilla/show_bug.cgi?id=40212";>40212</a>)
- but the mechanisms are not as well understood.</p>
+ clear all static members when unloading classes, however
+ this process can trigger initialization of classes which may
+ then call a class that has been cleared resulting in a
+ NullPointerException or some undesirable behavior.
+ Bug <a
href="http://issues.apache.org/bugzilla/show_bug.cgi?id=40212";>40212</a>)
+ describes the problem in detail and has a patch which at this
writing
+ has not been applied to Tomcat. Glassfish had a similar problem
+ and accepted the patch.</p>
- <p>The following have been recommended to avoid this problem:
+ <p>The following are recommended to avoid this problem:
<ol>
<li>Set the
org.apache.catalina.loader.WebappClassLoader.ENABLE_CLEAR_REFERENCES
system property to false.</li>
+ <li>Apply the patch from bug <a
href="http://issues.apache.org/bugzilla/show_bug.cgi?id=40212";>40212</a>
+ or upgrade to a version that has that patch
applied.</li>
<li>Upgrade to log4j 1.2.16 or later to better defend
against class loader attack
or provide a better diagnostic message when it does
occur.</li>
- <li>Use per-application copies of log4j, that is remove
log4j.jar from WEB-INF/lib.</li>
- <li>Avoid calls to log4j from within class
initialization.</li>
- <li>Upgrade to the latest version of the framework that
causing the problem.</li>
- <li>Use EnhancedPatternLayout from the extras companion
when the NPE occurs
- in a call of PatternLayout.</li>
</ol>
</p>
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