Question

I am totally new to Log4net. I have managed to get something going by adding a config file and simple logging. I have hardcoded the value to be "C:\temp\log.txt" but this is not good enough.

The logs must go to the special folders

path = Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData);

and this path changes depending whether you are using Windows Server 2008 or Windows XP or Vista etc…

How can I just change the location of the file in log4net programmatically?

This is what I have done:

<configSections>
<section name="log4net"
         type="log4net.Config.Log4NetConfigurationSectionHandler,Log4net"/>
</configSections>
<log4net>         
    <root>
        <level value="DEBUG" />
        <appender-ref ref="LogFileAppender" />
    </root>
    <appender name="LogFileAppender" type="log4net.Appender.RollingFileAppender">
        <param name="File" value="C:\temp\log.txt" />
        <param name="AppendToFile" value="true" />
        <rollingStyle value="Size" />
        <maxSizeRollBackups value="10" />
        <maximumFileSize value="10MB" />
        <staticLogFileName value="true" />
        <layout type="log4net.Layout.PatternLayout">
            <param name="ConversionPattern" value="%-5p%d{yyyy-MM-dd hh:mm:ss} – %m%n" />
        </layout>
    </appender>
</log4net>

---

class Program
{
    protected static readonly ILog log = LogManager.GetLogger(typeof(Program));

    static void Main(string[] args)
    {
        log4net.Config.XmlConfigurator.Configure();
        log.Warn("Log something");

        path = Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData);


        // How can I change where I log stuff?
    }
}

Just need to figure out how I can change to log stuff to where I want to.

Any suggestions?
Thanks a lot

Answer 1

log4net can handle this for you. Any appender property of type string can be formatted, in this case, using the log4net.Util.PatternString option handler. PatternString even supports the SpecialFolder enum which enables the following elegant config:

<appender name="LogFileAppender" type="log4net.Appender.RollingFileAppender" >
    <file type="log4net.Util.PatternString" 
        value="%envFolderPath{CommonApplicationData}\\test.txt" />
    ...
</appender>

Here’s a unit test that proofs the pudding:

[Test]
public void Load()
{
    XmlConfigurator.Configure();
    var fileAppender = LogManager.GetRepository()
        .GetAppenders().First(appender => appender is RollingFileAppender);

    var expectedFile = 
        Path.Combine(
            Environment.GetFolderPath(
                Environment.SpecialFolder.CommonApplicationData),
                "test.txt");

    Assert.That(fileAppender, 
        Is.Not.Null & Has.Property("File").EqualTo(expectedFile));
}

The following test verifies that log4net actually writes to disk (which basically makes this an “integration” test, not a unit test, but we’ll leave it at that for now):

[Test]
public void Log4net_WritesToDisk()
{
    var expectedFile = 
        Path.Combine(
            Environment.GetFolderPath(
                Environment.SpecialFolder.CommonApplicationData),
                "test.txt");

    if (File.Exists(expectedFile))
        File.Delete(expectedFile);

    XmlConfigurator.Configure();

    var log = LogManager.GetLogger(typeof (ConfigTest));
    log.Info("Message from test");

    LogManager.Shutdown();

    Assert.That(File.ReadAllText(expectedFile), 
        Text.Contains("Message from test"));
}

NB: I strongly suggest using the compact property syntax demonstrated in the above sample. Removing all those “<property name=” makes your config that much more readable.