ILogger

ILogger is a logging abstraction provided by Microsoft.Extensions.Logging in the .NET ecosystem. It defines a simple API for emitting log messages across different categories and destinations, allowing code to be decoupled from concrete logging implementations. The interface is widely used in ASP.NET Core and other .NET applications to route messages to multiple providers such as console, debug, file sinks, or external services.

The core interface exposes methods for logging at different levels, a means to check if a given level is enabled, and a mechanism to create logical scopes. The primary method is Log, parameterized by log level, EventId, state, exception, and a formatter function. There is also BeginScope to group related messages. Implementations also provide convenience extension methods such as LogInformation, LogWarning, LogError, etc., via LoggerExtensions.

ILogger<TCategoryName> is a commonly used generic variant that automatically sets the category name to the type TCategoryName. Implementations are provided by providers implementing ILoggerProvider, and typically constructed by an ILoggerFactory or through the host's logging builder. Configuration of minimum log level and providers is usually done in configuration files or in code.

Usage example: logger.LogInformation("Starting up"); These loggers are designed to be thread-safe and support structured logging by using state objects that can be formatted into messages. Overall, ILogger serves as a decoupled entry point for emitting log data, enabling flexible routing to diverse destinations without requiring direct dependencies on specific logging sinks.