Simple Log4Net example with VB.Net

Since I couldn’t find easily startup example for log4net written in VB.Net, I decided to write one for myself. In this example I’m using my favorite appender, the RollingFileAppender  that has fixed file size and one automatic backup.

See also:

1. http://vpalmu.wordpress.com/2007/09/27/simplest-ever-example-for-log4net-and-vbnet/
2. http://vpalmu.wordpress.com/2007/08/30/log4net-and-filename-com1txt/

Please download and install the last version of the log4net if you haven’t already done it. Create new windows application project.With VS2005 open, choose “File”, “New Project”. On New Project Window, choose “Windows application”,type “Log4NetApp” in the “Name” field, click ok. Open the Form1.vb, create five command buttons

1. “Debug”
2. “Info”
3. “Warn”
4. “Error”
5. “Fatal”

Form1.vb should look something like this on design view:

Add reference to log4net.dll, can be found on \bin\net\2.0\release directory inside of the log4net installation directory.

Add followig code for Form1.vb:

Imports log4net
Public Class Form1
Dim log As log4net.ILog
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
log = log4net.LogManager.GetLogger("MyApp")
log4net.Config.XmlConfigurator.Configure()
End Sub
Private Sub cmdDebug_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdDebug.Click
log.Debug("'Debug' level message")
End Sub
Private Sub cmdInfo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdInfo.Click
log.Info("'Info' level message")
End Sub

Private Sub cmdWarn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdWarn.Click
log.Warn("'Warning' level message")
End Sub

Private Sub cmdError_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdError.Click
log.Error("'Error' level message")
End Sub
Private Sub cmdFatal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdFatal.Click
log.Fatal("'Fatal' level message")
End Sub
End Class

Add application configuration file, right click Log4Net project on the Solution Explorer and choose “Add”, “New Item” and “Application Configuration File”. You can leave the default name app.config.

Open the App.config file, place under the configuration tag:

<configSections>
<section name=”log4net”
type=”log4net.Config.Log4NetConfigurationSectionHandler, log4net” />
</configSections>

Create new tag <log4net></log4net> under the </configSections> Open the tag, and place following inside of it:

<appender name=”RollingFileAppender” type=”log4net.Appender.RollingFileAppender”>
<file value=”c:\\log.txt” />
<appendToFile value=”true” />
<rollingStyle value=”Size” />
<maxSizeRollBackups value=”3″ />
<maximumFileSize value=”100KB” />
<staticLogFileName value=”true” />
<layout type=”log4net.Layout.PatternLayout”>
<conversionPattern value=”%date [%thread] %-5level %logger [%property{NDC}] – %message%newline” />
</layout>
</appender>

This defines the log appender that is going be used for your log (see doubles slashes for file value).

And finally, still inside the <log4net> tab,  the logger tab ties the .config file with your app, make sure that de logger name defined here is the same that you used for GetLogger method earlier.

<logger name=”MyApp”>
<level value=”DEBUG” />
<appender-ref ref=”RollingFileAppender” />
</logger>

Close the log4net tag with </log4net>.  Save everything and start your app with full compilation. When window show up click on the debug button and you should see your message on “c:\log.txt” file.

Change the level value on the logger tag in the app.confifg file from “DEBUG” to “ERROR”. After this all ”DEBUG”, “INFO” and “WARN” level messsages should have been filtered out.