log4j: errors to an errorFile - log4j

Question

I have a class which events I want to log. Say, there are 2 levels: debug and error. How can I log errors to an errorFile and debug info to a debugFile?
So that I use log4j.xml there is a filter mechanism, but it seems to work only for different categories not inside one class.
Please, help to newbie. =)

Answer 1

You have to define and use two appender with different Threshold like this:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<!-- Error -->
<appender name="ErrorFile"
class="org.apache.log4j.RollingFileAppender">
<param name="Threshold" value="error"/>
<param name="file" value="log.err" />
<param name="MaxFileSize" value="10MB" />
<param name="MaxBackupIndex" value="10" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d %C.%M (%L) - %m%n" />
</layout>
</appender>
<appender name="LogFile"
class="org.apache.log4j.RollingFileAppender">
<param name="Threshold" value="debug"/>
<param name="file" value="log.log" />
<param name="MaxFileSize" value="10MB" />
<param name="MaxBackupIndex" value="10" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d %C.%M (%L) - %m%n" />
</layout>
</appender>
<logger name="foo.bar" additivity="false">
<level value="debug" />
<appender-ref ref="LogFile" />
<appender-ref ref="ErrorFile" />
</logger>
<root>
<priority value="warn" />
<appender-ref ref="ErrorFile"/>
</root>
</log4j:configuration>
This question is also answered in the log4j FAQs.
Just found the LogToAppenderByLevel solution (here) which may be also helpful for you.