Logging during Application Startup

In some scenarios you need to log messages during the application startup, prior to any logging configuration.

This can be achieved by invoking a listener programmatically.

In the example below you will save Startup.cs events to a local text file using LocalTextFileListener.

using KissLog;
using KissLog.Listeners.FileListener;
using System;

namespace AspNetCore_WebApp
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;

            Logger logger = new Logger(url: "Startup");
            try
            {
                logger.Debug("Executing an important startup code");

                string message = null;
                int length = message.Length;    // will throw NullReferenceException
            }
            catch (Exception ex)
            {
                logger.Error(ex);
                throw;
            }
            finally
            {
                FlushLogArgs flushLogArgs = FlushLogArgsFactory.Create(new[] { logger });
                
                // programmatically invoke LocalTextFileListener
                var listener = new LocalTextFileListener("logs", FlushTrigger.OnFlush);
                listener.OnFlush(flushLogArgs);
            }
        }

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            // [ ... ]
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            // [ ... ]
        }
    }
}

The same concept can be followed for other scenarios.

In the example below you will save Global.asax events to a local text file using LocalTextFileListener.

using KissLog;
using KissLog.Listeners.FileListener;
using System;

namespace AspNet.Mvc
{
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            RouteConfig.RegisterRoutes(RouteTable.Routes);

            Logger logger = new Logger(url: "Application_Start");
            try
            {
                logger.Debug("Executing an important startup code");

                int value = 0;
                int result = 100 / value;    // will throw DivideByZeroException
            }
            catch (Exception ex)
            {
                logger.Error(ex);
                throw;
            }
            finally
            {
                FlushLogArgs flushLogArgs = FlushLogArgsFactory.Create(new[] { logger });

                // programmatically invoke LocalTextFileListener
                var listener = new LocalTextFileListener("logs", FlushTrigger.OnFlush);
                listener.OnFlush(flushLogArgs);
            }
        }

        // [ ... ]
    }
}