如何为类库包含log4net？

Question

I want to implement logging function into a class library, which is itself referenced in a webservice. I tried to add app.config and did everything needed, but it seems that when an exception is thrown, log4net simply does nothing.

my app.config

<configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
  </configSections>
  <log4net>
    <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
      <file value="D:\\mylogfile.txt" />
      <appendToFile value="true" />
      <rollingStyle value="Size" />
      <maxSizeRollBackups value="5" />
      <maximumFileSize value="10MB" />
      <staticLogFileName value="true" />
      <filter type="log4net.Filter.StringMatchFilter">
        <stringToMatch value="test" />
      </filter>
      <filter type="log4net.Filter.StringMatchFilter">
        <stringToMatch value="error" />
      </filter>
      <filter type="log4net.Filter.DenyAllFilter" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%thread] %level %logger - %message%newline%exception" />
      </layout>
    </appender>
    <root>
      <level value="INFO"/>
      <appender-ref ref="RollingFileAppender"/>
      <appender-ref ref="ConsoleAppender" />
    </root>
  </log4net>

in AssemblyInfo.cs:

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "app.config")]

in LogManager.cs:

private static readonly ILog Log = log4net.LogManager.GetLogger
            (MethodBase.GetCurrentMethod().DeclaringType);
public static void WriteLog(Exception ex)
{
    Log.Error(ex);
}

Can you please tell me what's wrong? How can I get log4net working for my class library?

Thank you

Answer 1

At runtime, config file is always used from host application, unless declared explicitly. Here in case, web.config is being used not app.cofig. Rather mention some other custom config file name and ensure that file is copied in virtual directory of web service. Also as chibacity said, ensure permission on log file. Better keep it in app_data folder for web service host.

Answer 2

You could use some kind of injection, either you build a simple one like:

public interface ILogger
{
    void LogInfo(string message);
       .
       .
       .
}

And then you just inject something that matches that interface, like a wrapper for log4net or such.

But, I think the most correct thing is to not log in the class library. Why I think so is because the library itself is not the application, your web service is so your web service should decide what to log. If you want to log exceptions just don't catch them in the class library and let your web service handle the logging. This will also make it easier to centralize the logging.

Answer 3

Please see my answer to the following question:

Use log4net in SDK

It has a log configuration routine that will construct a complete path to a log4net config file. As you are in a webservice it my not be looking where you expect for "app.config".

Also make sure that you have permission to write to "D:\\mylogfile.txt" from your webservice.