Friday, July 23, 2010

When Log4j Logs Messages Twice...

Since my Google'ing only gave me a clue instead of the complete answer on this one, I post it here for future reference.

When a given logger in a log4j configuration is outputting messages twice to your appender, you might try adding the additivity attribute as a fix:
<logger name="myLogger" additivity="false">
    <level value="info"/>
    <appender-ref ref="myFile"/>

Same idea for logger or for category. From the DTD (I'm using version 1.2.15):
<!ELEMENT category (param*,(priority|level)?,appender-ref*)>
<!ATTLIST category
  class         CDATA   #IMPLIED
  additivity (true|false) "true"  

<!ELEMENT logger (level?,appender-ref*)>
<!ATTLIST logger
  additivity (true|false) "true"  

This worked for me. As you can see, the additivity defaults to true. There may be other fixes, but I didn't dig any further after fixing my problem.

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