Implementation and usage of logger wrapper for log4net

Question

This question is related to Steven’s answer - here. He proposed a very good logger wrapper. I will paste his code below:

public interface ILogger
{
    void Log(LogEntry entry);
}

public static class LoggerExtensions
{
    public static void Log(this ILogger logger, string message)
    {
        logger.Log(new LogEntry(LoggingEventType.Information,
            message, null));
    }

    public static void Log(this ILogger logger, Exception exception)
    {
        logger.Log(new LogEntry(LoggingEventType.Error, 
            exception.Message, exception));
    }

    // More methods here.
}

So, my question is what is the proper way to create implementation that proxies to log4net? Should I just add another Log extension method with type parameter and then create a switch inside? Use different log4net method in case of LoggingEventType ?

And second question, what is the best way to use it later in the code?

Because he wrote:

(…) you can easily create an ILogger implementation (…) and configure your DI container to inject it in classes that have a ILogger in their constructor.

Does that mean that every class that will log sth (so basically every), should have ILogger in its constructor?

Answer 1

So, my question is what is the proper way to create implementation that proxies to log4net?

you should create something like:

public class Log4netAdapter : ILogger
{
    private readonly log4net.ILog m_Adaptee;

    public Log4netAdapter(log4net.ILog adaptee)
    {
        m_Adaptee = adaptee;
    }

    public void Log(LogEntry entry)
    {
        //Here invoke m_Adaptee
        if(entry.Severity == LoggingEventType.Debug)
            m_Adaptee.Debug(entry.Message, entry.Exception);
        else if(entry.Severity == LoggingEventType.Information)
            m_Adaptee.Info(entry.Message, entry.Exception);
        else if(entry.Severity == LoggingEventType.Warning)
            m_Adaptee.Warn(entry.Message, entry.Exception);
        else if(entry.Severity == LoggingEventType.Error)
            m_Adaptee.Error(entry.Message, entry.Exception);
        else
            m_Adaptee.Fatal(entry.Message, entry.Exception);
    }
}

Does that mean that every class that will log sth (so basically every), should have ILogger in its constructor?

As I understand from Stevens answer: Yes, you should do this.

what is the best way to use it later in the code?

If you are using a DI container, then just use the DI container to map ILogger to Log4netAdapter. You also need to register log4net.ILog, or just give an instance of log4net logger to the DI container to inject it to the Log4netAdapter constructor.

If you don't use a DI container, i.e., you use Pure DI, then you do something like this:

ILog log = log4net.LogManager.GetLogger("MyClass");

ILogger logging_adapter = new Log4netAdapter(log);

var myobject = new MyClass(other_dependencies_here, logging_adapter);