debugging messages to one file and other messages to another file. This can only be done with XML because we need a LevelRange filter.

log4j.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd" >
<log4j:configuration>
	<appender name="file"
		class="org.apache.log4j.RollingFileAppender">
		<param name="maxFileSize" value="100KB" />
		<param name="maxBackupIndex" value="5" />
		<param name="File" value="test.log" />
		<param name="threshold" value="info" />
		<layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern"
				value="%d{ABSOLUTE} %5p %c{1}:%L - %m%n" />
		</layout>
	</appender>
	<appender name="debugfile"
		class="org.apache.log4j.RollingFileAppender">
		<param name="maxFileSize" value="100KB" />
		<param name="maxBackupIndex" value="5" />
		<param name="File" value="debug.log" />
		<layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern"
				value="%d{ABSOLUTE} %5p %c{1}:%L - %m%n" />
		</layout>
		<filter class="org.apache.log4j.varia.LevelRangeFilter">
			<param name="LevelMin" value="debug" />
			<param name="LevelMax" value="debug" />
		</filter>
	</appender>

	<root>
		<priority value="debug"></priority>
		<appender-ref ref="debugfile" />
		<appender-ref ref="file" />
	</root>
</log4j:configuration>

The Above from http://www.laliluna.de/articles/log4j-tutorial.html