In this article, I will show you how to edit the Log4j configuration file of a Mule project to split the logs into multiple files based on log levels. The same can also be achieved in JAVA/J2EE.

In this example, we will split the log files for two log levels (debug, error).

Tools Used: Anypoint Studio version 6.2.3 for Windows.

Let's Start

Step 1: Inside the Mule project -> src/main/resources. Double click on log4j2.xml file to open in Anypoint Studio.

Step 2: Create multiple RollingFile configs within the Apenders tag. I will create two for this example, as we are going to generate only two log files. You can create as many as needed per the log levels.

Also, you can name the Rolling file config as per your needs; for this, I will be using "debugLogFile" and "errorLogFile."

<RollingFile name="debugLogFile" 
             fileName="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}${applicationName}-debugLogFile.log" 
             filePattern="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}archive${sys:file.separator}${applicationName}-debugLogFile-%d{yyyy-MM-dd-HH:mm:ss:SSS}.log.gz">
 <RollingFile name="errorLogFile" 
              fileName="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}${applicationName}-errorLogFile.log" 
              filePattern="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}archive${sys:file.separator}${applicationName}-errorLogFile-%d{yyyy-MM-dd-HH:mm:ss:SSS}.log.gz">

Step 3: Add Filters within the Rolling file to restrict the logs flowing into a particular log file.

<Filters>
<ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="NEUTRAL" />
<ThresholdFilter level="FATAL" onMatch="DENY" onMismatch="NEUTRAL" />
</Filters>

Step 4: Control logging by using a reference to the correct Rolling file.

<AsyncLogger name="org.mule" level="error">
<AppenderRef ref="errorLogFile" level="error"/>
</AsyncLogger>

<AsyncLogger name="com.mulesoft" level="debug">
<AppenderRef ref="debugLogFile" level="debug"/>
</AsyncLogger>

Voila! Your multiple logging solution is ready. 

Here is the complete log4j2.xml code:

<?xml version="1.0" encoding="utf-8"?>
<Configuration>
    <Properties>
      <Property name="applicationName">split-log-file</Property>
    </Properties>

    <Appenders>
      <RollingFile name="debugLogFile" fileName="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}${applicationName}-debugLogFile.log" 
                   filePattern="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}archive${sys:file.separator}${applicationName}-debugLogFile-%d{yyyy-MM-dd-HH:mm:ss:SSS}.log.gz">
        <PatternLayout pattern="%d [%t] %-5p %c - %m%n" />
        <SizeBasedTriggeringPolicy size="50 MB"/>
        <Filters>
        <ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="NEUTRAL" />
            <ThresholdFilter level="FATAL" onMatch="DENY" onMismatch="NEUTRAL" />
        </Filters>
      </RollingFile>
      <RollingFile name="errorLogFile" fileName="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}${applicationName}-errorLogFile.log" 
                   filePattern="${sys:mule.home}${sys:file.separator}logs${sys:file.separator}archive${sys:file.separator}${applicationName}-errorLogFile-%d{yyyy-MM-dd-HH:mm:ss:SSS}.log.gz">
        <PatternLayout pattern="%d [%t] %-5p %c - %m%n" />
        <SizeBasedTriggeringPolicy size="10 MB"/>
      </RollingFile>
    </Appenders>

    <Loggers>
        <!-- CXF is used heavily by Mule for web services -->
        <AsyncLogger name="org.apache.cxf" level="WARN">
        <AppenderRef ref="errorLogFile" level="ERROR"/>
        </AsyncLogger>

        <!-- Apache Commons tend to make a lot of noise which can clutter the log-->
        <AsyncLogger name="org.apache" level="WARN">
        <AppenderRef ref="errorLogFile" level="ERROR"/>
        </AsyncLogger>

        <!-- Reduce startup noise -->
        <AsyncLogger name="org.springframework.beans.factory" level="WARN">
        <AppenderRef ref="errorLogFile" level="ERROR"/>
        </AsyncLogger>

        <!-- Mule classes -->
        <AsyncLogger name="org.mule" level="debug">
        <AppenderRef ref="errorLogFile" level="ERROR"/>
        </AsyncLogger>
        <AsyncLogger name="com.mulesoft" level="debug">
        <AppenderRef ref="errorLogFile" level="ERROR"/>
        </AsyncLogger>
<AsyncLogger name="org.mule.module.http*" level="WARN">
<AppenderRef ref="errorLogFile" level="ERROR"/>
</AsyncLogger>

        <!-- Reduce DM verbosity -->
        <AsyncLogger name="org.jetel" level="WARN">
        <AppenderRef ref="errorLogFile" level="ERROR"/>
        </AsyncLogger>
        <AsyncLogger name="Tracking" level="WARN">
        <AppenderRef ref="errorLogFile" level="ERROR"/>
        </AsyncLogger>

<!-- Sending normal debug logs to debugLogFile -->
        <AsyncRoot level="debug">
            <AppenderRef ref="debugLogFile" />
        </AsyncRoot>
    </Loggers>

</Configuration>

Now, Run your project and go to Workspace -> .mule -> logs folder. You will see two log files created based on the log levels and as per the name you configured.

Let's call it a day!