How do you configure and enable log4net for a stand-alone class library assembly?

Asked 22/6, 2009 at 17:10 Answered 25/10, 2019 at 17:37

Background

I am writing a class library assembly in C# .NET 3.5 which is used for integration with other applications including third-party Commercial-Off-The-Shelf (COTS) tools. Therefore, sometimes this class library will be called by applications (EXEs) that I control while other times it will be called by other DLLs or applications that I do not control.

Assumptions

I am using C# 3.0, .NET 3.5 SP1, and Visual Studio 2008 SP1
I am using log4net 1.2.10.0 or greater

Constraints

Any solution must:

Allow for the class library to enable and configure logging via it's own configuration file, if the calling application does not configure log4net.
Allow for the class library to enable and configuring logging via the calling applications configuration, if it specifies log4net information

Allow for the class library to enable and configuring logging using it's own configuration file at all times.

Problem

When my stand-alone class library is called by a DLL or application that I do not control (such as a third-party COTS tool) and which doesn't specify log4net configuration information, my class library is unable to do any of it's logging.

Question

How do you configure and enable log4net for a stand-alone class library assembly so that it will log regardless if the calling application provides log4net configuration?

Summersault answered 22/6, 2009 at 17:10 Comment(0)

Solution 1

A solution for the first set of constraints is to basically wrap the log4net.LogManager into your own custom LogManager class like Jacob, Jeroen, and McWafflestix have suggested (see code below).

Unfortunately, the log4net.LogManager class is static and C# doesn't support static inheritance, so you couldn't simply inherit from it and override the GetLogger method. There aren't too many methods in the log4net.LogManager class however, so this is certainly a possibility.

The other drawback to this solution is that if you have an existing codebase (which I do in my case) you would have to replace all existing calls to log4net.LogManager with your wrapper class. Not a big deal with today's refactoring tools however.

For my project, these drawbacks outweighed the benefits of using a logging configuration supplied by the calling application so, I went with Solution 2.

Code

First, you need a LogManager wrapper class:

using System;
using System.IO;
using log4net;
using log4net.Config;

namespace MyApplication.Logging
{
    //// TODO: Implement the additional GetLogger method signatures and log4net.LogManager methods that are not seen below.
    public static class LogManagerWrapper
    {
        private static readonly string LOG_CONFIG_FILE= @"path\to\log4net.config";

        public static ILog GetLogger(Type type)
        {
            // If no loggers have been created, load our own.
            if(LogManager.GetCurrentLoggers().Length == 0)
            {
                LoadConfig();
            }
            return LogManager.GetLogger(type);
        }

        private void LoadConfig()
        {
           //// TODO: Do exception handling for File access issues and supply sane defaults if it's unavailable.   
           XmlConfigurator.ConfigureAndWatch(new FileInfo(LOG_CONFIG_FILE));
        }              
}

Then in your classes, instead of:

private static readonly ILog log = LogManager.GetLogger(typeof(MyApp));

Use:

private static readonly ILog log = LogManagerWrapper.GetLogger(typeof(MyApp));

Solution 2

For my purposes, I have decided to settle on a solution that meets the second set of constraints. See the code below for my solution.

From the Apache log4net document:

"An assembly may choose to utilize a named logging repository rather than the default repository. This completely separates the logging for the assembly from the rest of the application. This can be very useful to component developers that wish to use log4net for their components but do not want to require that all the applications that use their component are aware of log4net. It also means that their debugging configuration is separated from the applications configuration. The assembly should specify the RepositoryAttribute to set its logging repository."

Code

I placed the following lines in the AssemblyInfo.cs file of my class library:

// Log4Net configuration file location
[assembly: log4net.Config.Repository("CompanyName.IntegrationLibName")]
[assembly: log4net.Config.XmlConfigurator(ConfigFile = "CompanyName.IntegrationLibName.config", Watch = true)]

References

Summersault answered 22/6, 2009 at 18:39 Comment(4)

My particular situation would be served well by following the solution 2 as well. I was just wondering how to solve this too. Thanks for the insight! – Cogitation 29/3, 2013 at 13:57

If you're going to lazily load your config on first call to GetLogger, it should be protected in a synchronized block. But I suggest loading config when the application loads, so you can explicitly define a failover strategy. – Emf 24/4, 2015 at 13:2

your getLogger method is void but returns an ILog? – Ambiguity 4/11, 2015 at 20:11

LoadConfig() must be static if it's called from a static method. ;-) – Succeed 18/10, 2017 at 10:19

You can probably code something around the XmlConfigurator class:

public static class MyLogManager
{
    // for illustration, you should configure this somewhere else...
    private static string configFile = @"path\to\log4net.config";

    public static ILog GetLogger(Type type)
    {
        if(log4net.LogManager.GetCurrentLoggers().Length == 0)
        {
            // load logger config with XmlConfigurator
            log4net.Config.XmlConfigurator.Configure(configFile);
        }
        return LogManager.GetLogger(type);
    }
}

Then in your classes, instead of:

private static readonly ILog log = LogManager.GetLogger(typeof(MyApp));

Use:

private static readonly ILog log = MyLogManager.GetLogger(typeof(MyApp));

Of course, it would be preferable to make this class a service and dynamically configure it with the IoC container of your choice, but you get the idea?

EDIT: Fixed Count() problem pointed out in comments.

Seleta answered 22/6, 2009 at 17:23 Comment(6)

Ohhh, nice. This answers the question I was asking McWafflestix and Jeroen Huinink (I would imagine they had thought about this as well). Let me give this a whirl quickly. – Summersault 22/6, 2009 at 17:33

@Jacob: it seems to me that the condition you are checking Count() > 0 is wrong. Shouldn't it read Count() = 0? – Ferricyanide 22/6, 2009 at 17:42

If you have multiple classes in your library then Jacob's solution makes sense. If you have only one you could implement my solution. This avoids the need for an extra class. – Ferricyanide 22/6, 2009 at 17:43

I believe Jeroen is correct, the condition should be == 0. Also, it's .Length not .Count. I'm working out this idea in my current solution. I'll get back shortly with more details. Thanks! – Summersault 22/6, 2009 at 17:49

D'Oh, of course. This is a bit of a hack though. I'm sure log4net has some sort of configuration mechanism that would allow you to override GetLogger(type) without the need for a custom class, something like a LoggerResolver... – Seleta 22/6, 2009 at 17:56

You might also want to change to return type of GetLogger to ILogger instead of void. – Ruralize 20/1, 2010 at 15:30

In your code you can check if there are any loggers via

log4net.LogManager.GetCurrentLoggers().Count()

You could then for example use an XmlConfigurator to load a default configuration from a file:

log4net.Config.XmlConfigurator.Configure(configFile)

You could do the initialization in a static or regular constructor.

class Sample
{
    private static readonly log4net.ILog LOG;

    static Sample()
    {
        if (log4net.LogManager.GetCurrentLoggers().Count() == 0)
        {
            loadConfig();
        }
        LOG = log4net.LogManager.GetLogger(typeof(Sample));

    }

    private static void loadConfig()
    {
        /* Load your config file here */
    }

    public void YourMethod()
    {
       LOG.Info("Your messages");
    }
}

Ferricyanide answered 22/6, 2009 at 17:27 Comment(2)

This sounds promising. Similar to my comment to McWafflestix, how would I perform this check and call to Configure in such a manner that it is guaranteed to execute before any logging calls are made in the class library without wrapping all logging calls into a separate class? In otherwords, there is no "main" in my class assembly where I can perform this check - they can call into my assembly where ever they want. I would like to avoid wrapping log4net if possible. – Summersault 22/6, 2009 at 17:31

XmlConfigurator to load a default configuration from a file how will the code know which Logger name too load configuration for? – Heaven 15/11, 2012 at 12:43

In your standalone class library, have a singleton which loads the log4net configuration file using the log4net.Config.XmlConfigurator.

Specifically, you can define all of your code to use your own custom logging class; this class can just be a simple wrapper of the log4net logging calls, with one addition; make a static member which contains the log information you want to log to; initialize that with a call to the XmlConfigurator in the static constructor for that class. That's all you have to do.

Freeswimming answered 22/6, 2009 at 17:19 Comment(1)

How would I be sure that my singleton would be called since they could be calling any number of methods or classes within my library? Wouldn't I have to wrap all of my logging calls into the singleton class so that I could enforcing loading, if necessary? Thanks! – Summersault 22/6, 2009 at 17:23

You can find a good description here: log4net: A quick start guide

As the article describes, to configure it fore each assembly separately, create an XML file for your assembly named AssemblyName.dll.log4net and place the following XML code into it:

<?xml version="1.0" encoding="utf-8"?>
<log4net debug="false">
   <appender name="XmlSchemaFileAppender" type="log4net.Appender.FileAppender">
      <file value="AppLog.xml" />
      <appendToFile value="true" />
      <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
      <layout type="log4net.Layout.XmlLayout" />
   </appender>

   <root>
      <level value="WARN" />
      <appender-ref ref="XmlSchemaFileAppender" />
   </root>
</log4net>

It further describes, to instantiate a new logger, simply declare it as a variable for the entire class as follows:

public class LogSample
{
    private static readonly log4net.ILog Log 
            = log4net.LogManager.GetLogger(typeof(LogSample));
    // Class Methods Go Here...
}

You can then use the private variable Log inside your class like:

Log.Info("Sample message");

Likewise you can use Log.Error("Error occurred while running myMethod", ex) to log errors along with the exception details.

What I found is the following:

Don't forget to call log4net.Config.XmlConfigurator.Configure(); to activate your configuration
If you need to know the path of the file(s) written, here some code how to obtain it from Log4Net

I hope this helps.

Rave answered 14/6, 2016 at 11:6 Comment(0)

This works for me for a shared library

protected static readonly log4net.ILog log = log4net.LogManager.GetLogger(System.Reflection.Assembly.GetExecutingAssembly().GetType());

Wonky answered 25/10, 2019 at 17:37 Comment(0)

Hot tags

Godot Unity Godot Help Programming Godot 4.X GUI GDScript 3D 2D Physics CSharp Godot 3.X VR XR Projects C++

Background

Assumptions

Constraints

Problem

Question

Solution 1

Code

Solution 2

Code

References

Recommended topics

Hot tags