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+++ b/content/Java/log4j-logger-additivity.md	Fri Jun 28 08:48:58 2013 +0200
@@ -0,0 +1,18 @@
+Title: Log4j and logger additivity
+Date: 2008-02-18
+Tags: log4j, logging
+Lang: en
+
+Sometimes you want to write more than one logfile using logj4. This is possible by defining multiple appenders and specifying an appender for a certain logger like this:
+
+    log4j.appender.A1=org.apache.log4j.ConsoleAppender
+    ....
+    log4j.appender.A2=org.apache.log4j.FileAppender
+    ....
+
+    log4j.rootLogger=DEBUG, A1
+    log4j.logger.foo=DEBUG, A2
+
+Unfortunately, all output that goes through the logger foo comes out in both appenders, which may not be what you want. The log4j docs talk about *logger additivity* but don't show concrete examples how to configure it. The trick is to configure the additivity **on the logger** and **not on the appender**. (I always fall into that trap). Simply add the following to the example above to stop messages to logger foo come out on A1:
+
+    log4j.additivity.foo = false