how to add .net core logger code example

Example 1: .net core logging level

namespace Microsoft.Extensions.Logging
{
    /// <summary>
    /// Defines logging severity levels.
    /// </summary>
    public enum LogLevel
    {
        /// <summary>
        /// Logs that contain the most detailed messages. These messages may contain sensitive application data.
        /// These messages are disabled by default and should never be enabled in a production environment.
        /// </summary>
        Trace = 0,

        /// <summary>
        /// Logs that are used for interactive investigation during development.  These logs should primarily contain
        /// information useful for debugging and have no long-term value.
        /// </summary>
        Debug = 1,

        /// <summary>
        /// Logs that track the general flow of the application. These logs should have long-term value.
        /// </summary>
        Information = 2,

        /// <summary>
        /// Logs that highlight an abnormal or unexpected event in the application flow, but do not otherwise cause the
        /// application execution to stop.
        /// </summary>
        Warning = 3,

        /// <summary>
        /// Logs that highlight when the current flow of execution is stopped due to a failure. These should indicate a
        /// failure in the current activity, not an application-wide failure.
        /// </summary>
        Error = 4,

        /// <summary>
        /// Logs that describe an unrecoverable application or system crash, or a catastrophic failure that requires
        /// immediate attention.
        /// </summary>
        Critical = 5,

        /// <summary>
        /// Not used for writing log messages. Specifies that a logging category should not write any messages.
        /// </summary>
        None = 6,
    }
}

Example 2: asp.net core logger in startup

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILogger<Startup> logger)
{
    logger.LogInformation("Configure called");

    // …
}