log4net后备附加程序配置是否丢失配置文件？

Question

I've got a C# (.NET 3.5) application that extensively use log4net. The log4net configuration resides in the app.config file.

Configuration is done using [assembly: XmlConfigurator(Watch = true)] in AssemlyInfo.cs App uses single application-wide logger instance, instantiated in a static constructor of a logger wrapper class:

public class Logger{
    //....
    private static readonly ILog logger;
    static Logger()
    {
        logger = LogManager.GetLogger(Assembly.GetEntryAssembly().GetName().Name);

        AppDomain.CurrentDomain.UnhandledException += OnUnhandledException;
    }
    //....
}

The app is designed to be run on distant server, by scheduler, with no human presense, alone in the dark. :) The problem is, in case of missing config file it just silently crashes (no log4net config => no logging).

Are there any way to check if there are any appenders in the config, and if not - programmatically add some kind of fallback appender.

I'm rather new to log4X loggers family, so, if I'm asking something trivial - please be kind, log4net documentation is really awful. :)

Answer 1

Ok, the question already on google, and I've found the answer, so I'll just left it here. :)

The key to manipulating appenders is a IAppenderAttachable interface, since it implements AddAppender , removeAppender methods.

What's returned by LogManager.GetLogger() is an instance of ILog , which in turn contains property Logger . The object returned by the ILog.Logger is a Logger class instance. Logger class implements IAppenderAttachable interface and contains Repository property to extract repository of the logger. Repository has method GetAppenders that returns AppenderCollection class instance (implements ICollection , IList , Ienumerable , etc.) with all the active appenders of the logger.

To sum up:

//no need to put it in the static constructor, but in my case it is so
static Logger() 
{
    logger = LogManager.GetLogger(...);
    if (logger.Logger.Repository.GetAppenders().Length == 0) {
        (logger.Logger as IAppenderAttachable).AddAppender(CreateConsoleAppender());
    }
}

private static ConsoleAppender CreateConsoleAppender()
{
    var appender = new ConsoleAppender();
    appender.Layout = CreateDefaultLayout();
    appender.AddFilter(CreateDefaultFilter());
    appender.ActivateOptions(); // if omitted - throws an excpetion
    log4net.Config.BasicConfigurator.Configure(appender); //if omitted - no errors, but logging does not work
    return appender;
}

private static ILayout CreateDefaultLayout()
{
    PatternLayout layout = new PatternLayout();
    layout.ConversionPattern = "%d{yyyy-MM-dd hh:mm:ss} - %level %m%n";
    layout.ActivateOptions();
    return layout;
}


private static IFilter CreateDefaultFilter()
{
    LevelRangeFilter filter = new LevelRangeFilter { LevelMin = Level.Info };
    filter.ActivateOptions();
    return filter;
}

Note that in case of missing or corrupted file log4net does not throw any exceptions (at least out of the box), but have no appenders attached to logger.