One of the greatest logging tools out there for .NET is log4net. This software is the gold standard for how logging should be done. It is simple, powerful, and extensible. The best part is that it is part of the FOSS community. What could be better? The one thing I see that is, in my opinion, a bit lacking is a straight-forward tutorial on how to use log4net. The documentation covers, in depth, how to use the software, but it is a bit obscure. Basically, if you already know what log4net can do and you just want to know the syntax, the documentation is for you. The tutorials out there usually cover one piece or one type of system. I am hoping to at least add to the tutorials that are out there, and maybe I might just provide you with a complete tutorial including questions to some of the problems I encountered. The below examples and information are based upon the documentation provided by the log4net group.
There are a three parts to log4net. There is the configuration, the setup, and the call. The configuration is typically done in the app.config or web.config file. We will go over this in depth below. If you desire more flexibility through the use of a separate configuration file, see the section titled "Getting Away from app.config". Either way you choose to store the configuration information, the code setup is basically a couple of lines of housekeeping that need to be called in order to set up and instantiate a connection to the logger. Finally, the simplest part is the call itself. This, if you do it right, is very simple to do and the easiest to understand.
There are seven logging levels, five of which can be called in your code. They are as follows (with the highest being at the top of the list):
OFF - nothing gets logged (cannot be called)FATALERRORWARNINFODEBUGALL - everything gets logged (cannot be called)These levels will be used multiple times, both in your code as well as in the config file. There are no set rules on what these levels represent (except the first and last).
The standard way to set up a log4net logger is to utilize either the app.config file in a desktop application or the web.config file in a web application. There are a few pieces of information that need to be placed in the config file in order to make it work properly with log4net. These sections will tell log4net how to configure itself. The settings can be changed without re-compiling the application, which is the whole point of a config file.
You need to have one root section to house your top-level logger references. These are the loggers that inherit information from your base logger (root). The only other thing that the root section houses is the minimum level to log. Since everything inherits from the root, no appenders will log information below that specified here. This is an easy way to quickly control the logging level in your application. Here is an example with a default level of INFO (which means DEBUG messages will be ignored) and a reference to two appenders that should be enabled under root:
Collapse | Copy Code <root> <level value="INFO"/> <appender-ref ref="FileAppender"/> <appender-ref ref="ConsoleAppender" /> </root>Sometimes you will want to know more about a particular part of your application. log4net anticipated this by allowing you to specify additional logger references beyond just the root logger. For example, here is an additional logger that I have placed in our config file to log to the console messages that occur inside the OtherClass class object:
Collapse | Copy Code <logger name="Log4NetTest.OtherClass"> <level value="DEBUG"/> <appender-ref ref="ConsoleAppender"/> </logger>Note that the logger name is the full name of the class including the namespace. If you wanted to monitor an entire namespace, it would be as simple as listing just the namespace you wanted to monitor. I would recommend against trying to re-use appenders in multiple loggers. It can be done, but you can get some unpredictable results.
In a config file where there will (potentially) be more information stored beyond just the log4net configuration information, you will need to specify a section to identify where the log4net configuration is housed. Here is a sample section that specifies that the configuration information will be stored under the XML tag "log4net":
Collapse | Copy Code <configSections> <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/> </configSections>An appender is the name for what logs the information. It specifies where the information will be logged, how it will be logged, and under what circumstances the information will be logged. While each appender has different parameters based upon where the data will be going, there are some common elements. The first is the name and type of the appender. Each appender must be named (anything you want) and have a type assigned to it (specific to the type of appender desired). Here is an example of an appender entry:
Collapse | Copy Code <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender">Inside of each appender must be a layout section. This may be a bit different depending on the type of appender being used, but the basics are the same. You need a type that specifies how the data will be written. There are multiple options, but the one that I suggest you use is the pattern layout type. This will allow you to specify how you want your data written to the data repository. If you specify the pattern layout type, you will need a sub-tag that specifies a conversion pattern. This is the pattern by which your data should be written to the data repository. I will give a more detailed description of your options for the conversion patterns, but for now, here is an example of the layout tag with the pattern layout specified:
Collapse | Copy Code <layout type="log4net.Layout.PatternLayout"> <conversionPattern value="