ASP.NET ILogger

last modified April 3, 2025

In this article, we explore the ILogger interface in ASP.NET 8. This interface provides a powerful logging abstraction for .NET applications. It helps track application behavior and diagnose issues.

ASP.NET is a cross-platform, high-performance framework for building modern web applications. ILogger is part of Microsoft.Extensions.Logging namespace. It supports structured logging and multiple logging providers.

Basic Definition

ILogger is a generic interface that provides methods for logging messages at different severity levels. It's part of .NET's built-in logging infrastructure.

The interface supports six log levels: Trace, Debug, Information, Warning, Error, and Critical. Each level represents increasing severity of logged events.

ILogger works with various logging providers like Console, Debug, EventLog, and third-party solutions. It supports dependency injection out of the box in ASP.NET.

ASP.NET ILogger Example

The following example demonstrates using ILogger in an ASP.NET 8 Web API controller.

var builder = WebApplication.CreateBuilder(args);

// Configure logging
builder.Logging.ClearProviders();
builder.Logging.AddConsole();
builder.Logging.AddDebug();

builder.Services.AddControllers();

var app = builder.Build();

app.MapControllers();
app.Run();

This sets up a basic ASP.NET application with console and debug logging. The ClearProviders removes default providers before adding our choices.

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;

[ApiController]
[Route("[controller]")]
public class WeatherController : ControllerBase
{
    private readonly ILogger<WeatherController> _logger;
    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild",
        "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

    public WeatherController(ILogger<WeatherController> logger)
    {
        _logger = logger;
        _logger.LogInformation("WeatherController initialized");
    }

    [HttpGet]
    public IEnumerable<WeatherForecast> Get()
    {
        _logger.LogDebug("Entering Get method");
        
        try
        {
            var rng = new Random();
            var forecasts = Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = rng.Next(-20, 55),
                Summary = Summaries[rng.Next(Summaries.Length)]
            })
            .ToArray();

            _logger.LogInformation("Generated {Count} weather forecasts", forecasts.Length);
            return forecasts;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error generating weather forecasts");
            throw;
        }
        finally
        {
            _logger.LogDebug("Exiting Get method");
        }
    }
}

public record WeatherForecast(DateTime Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}

This controller demonstrates various ILogger usage patterns. The logger is injected via constructor injection with the specific type ILogger<WeatherController>.

The example shows logging at different levels: Information for initialization, Debug for method entry/exit, and Error for exceptions. The LogInformation call demonstrates structured logging with the count parameter.

The LogError method captures both the error message and the exception object. This provides full stack trace information in the logs. Structured logging helps with log analysis and filtering.

When running this application, log messages will appear in both the console output and debug output windows. The log level can be configured in appsettings.json.

Source

Microsoft Logging Documentation

In this article, we have explored the ILogger interface in ASP.NET 8. This powerful logging abstraction helps monitor application behavior and diagnose issues effectively.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

List all ASP.NET tutorials.