log4net XmlConfigurator Simplified

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Contents

• Introduction
• Definitions
• How the Objects Relate to Each Other
• The Configuration
  • Appender Configuration
  • Assigning Appenders to Loggers
• Summary
• History
• References

Introduction

Many of us from time to time have struggled with configuring log4net. I know that in just about every application that I have worked on, I have taken a log4net configuration file, copied it and changed it to my liking. Well after some research and fiddling around with the configuration options available in log4net, I have come up with some interesting discoveries.

The first is that we can easily create separate log file / appenders for each class, assembly or even namespace if we want. Before I give you the answer, I want to tell you a little bit about the log4net library.

Definitions

log4net is essentially made up of six objects: log4net, log4net.Appender, log4net.Config, log4net.Filter, log4net.Layout and log4net.Repository. Here are their definitions:

• ILog interface is what is used for logging messages.
• LogManager is used to keep record of all of the loggers. A logger is an object that wants to log some data.
• Appender is an object that writes log data to some data store, application or library.
• Filter is a condition that can be applied to an Appender to restrict the writing of log data.
• Layout is the display formatting that will be used for the log data when it is written to the Appender.
• Repository is the central store for the log4net configuration and LogManager.

How the Objects Relate to Each Other

Each repository has one LogManager. Each LogManager has one or more Loggers. Each logger has one or more Appenders. Each Appender has one or more filters and one layout.

The Configuration

The easiest and most flexible way to configure log4net is with XML files. log4net provides a configuration reader for XML files in the log4net.Config.XmlConfigurator class. The XML file is comprised of two parts (that I know of). The first is one or more Appender definitions, the second defines the loggers and Appender definitions to a logger in the repository.

The <log4net> element supports the following attributes:

The <log4net> element supports the following child elements:

Appender Configuration

Each appender has different configuration options. The XML element looks similar to this:

<appender name="rootRollingFile" type="log4net.Appender.RollingFileAppender,log4net">
 <threshold value="ALL"/>
 <param name="File" value="logs/MasterLog"/>
 <param name="AppendToFile" value="true"/>
 <param name="RollingStyle" value="Date"/>
 <param name="DatePattern" value=".yyyy.MM.dd.'log'"/>
 <param name="StaticLogFileName" value="false"/>
 <layout type="log4net.Layout.PatternLayout,log4net">
  <param name="ConversionPattern" value="%date 
	[%-5thread] %-5level %logger - %message%newline %exception"/>
 </layout>
</appender>

The <appender> element supports the following attributes:

The <appender> element supports the following child elements:

Assigning Appenders to Loggers

There are two elements that are used for assigning Appenders to loggers, root and logger. With each of these elements, you can assign two child elements, level and appender-ref.
The <level> element tells log4net what log messages will be sent to this appender, this is the equivalent to the <threshold> element on the appender. The <appender-ref> element is used to assign the appender to the specific logger. The format of the element is <appender-ref ref="nameOfAppender" /> where the nameOfAppender is the name that was specified in the name attribute of the <appender> element.

When the <root> element is used, all logging message for the LogManager / logging Repository will be written to these appenders.
The <logger> element has one attribute, name, the name attribute can be a namespace, class, or object name that you want to attach a special appender to. This is how we are going to be able to attach a different appender for each class or library.

<root>
 <level value="ALL"/>
 <appender-ref ref="rootTrace"/>
 <appender-ref ref="rootConsole"/>
 <appender-ref ref="rootRollingFile"/>
 <appender-ref ref="rootEventLog"/>
</root>
<logger name="MyCompany">
 <level value="WARN" />
 <appender-ref ref="MyCompany_rollingFile" />
</logger>
<logger name="MyCompany.MultipleClasses">
 <level value="WARN" />
 <appender-ref ref="MyCompany_Multiple_rollingFile" />
</logger>
<logger name="MyCompany.MultipleClasses.Class1">
 <level value="DEBUG" />
 <appender-ref ref="class1File" />
</logger>
<logger name="MyCompany.MultipleClasses.Class2">
 <level value="DEBUG" />
 <appender-ref ref="class2File" />
</logger>
<logger name="MyCompany.MultipleClasses.Class3">
 <level value="DEBUG" />
 <appender-ref ref="class3File" />
</logger>
<logger name="MyCompany.Library1.MyFirstClass">
 <level value="DEBUG" />
 <appender-ref ref="lib1_MyFirstClass_File" />
</logger>
<logger name="MyCompany.Library2.MySecondClass">
 <level value="DEBUG" />
 <appender-ref ref="lib2_MySecondClass_File" />
</logger>
<logger name="MyCompany.Library2.MyThirdClass">
 <level value="DEBUG" />
 <appender-ref ref="lib2_MyThirdClass_File" />
</logger>

With this in mind, by looking at the configuration above, we can determine the following:

Summary

I know this was a lot to digest. If you have any questions, thoughts or comments on this article, please feel free to let me know.

References

• log4net Home
• log4net Configuration

History