3.1,自定义日志框架

本节示例项目在 Demo2.MyLogger.Console 中。

创建控制台项目后，添加 Microsoft.Extensions.Logging.Console 引用。

创建 MyLoggerOptions ，存储日志配置：

    public class MyLoggerOptions
    {
        /// <summary>
        /// 最小日志等级
        /// </summary>
        public LogLevel DefaultLevel { get; set; } = LogLevel.Debug;
    }

创建自定义日志记录器：

    /// <summary>
    /// 自定义的日志记录器
    /// </summary>
    public class MyConsoleLogger : ILogger
    {
        // 日志名称
        private readonly string _name;
        private readonly MyLoggerOptions _options;

        public MyConsoleLogger(string name, MyLoggerOptions options)
        {
            _name = name;
            _options = options;
        }

        public IDisposable? BeginScope<TState>(TState state) where TState : notnull => default!;

        // 判断是否启用日志等级
        public bool IsEnabled(LogLevel logLevel)
        {
            return logLevel >= _options.DefaultLevel;
        }

        // 记录日志，formatter 由框架提供的字符串格式化器
        public void Log<TState>(
            LogLevel logLevel,
            EventId eventId,
            TState state,
            Exception? exception,
            Func<TState, Exception?, string> formatter)
        {
            if (!IsEnabled(logLevel))
            {
                return;
            }
            if (logLevel == LogLevel.Critical)
            {
                System.Console.ForegroundColor = System.ConsoleColor.Red;
                System.Console.WriteLine($"[{logLevel}] {_name} {formatter(state, exception)} {exception}");
                System.Console.ResetColor();
            }
            else if (logLevel == LogLevel.Error)
            {
                System.Console.ForegroundColor = System.ConsoleColor.DarkRed;
                System.Console.WriteLine($"[{logLevel}] {_name} {formatter(state, exception)} {exception}");
                System.Console.ResetColor();
            }
            else
            {
                System.Console.WriteLine($"[{logLevel}] {_name} {formatter(state, exception)} {exception}");
            }
        }
    }

创建自定义日志提供器：

    [ProviderAlias("MyConsole")]
    public sealed class MyLoggerProvider : ILoggerProvider
    {
        private MyLoggerOptions _options;
        private readonly ConcurrentDictionary<string, MyConsoleLogger> _loggers =
            new(StringComparer.OrdinalIgnoreCase);

        public MyLoggerProvider(MyLoggerOptions options)
        {
            _options = options;
        }

        public ILogger CreateLogger(string categoryName) =>
            _loggers.GetOrAdd(categoryName, name => new MyConsoleLogger(name, _options));

        public void Dispose()
        {
            _loggers.Clear();
        }
    }

编写扩展函数，注入自定义日志提供器：

    public static class MyLoggerExtensions
    {
        public static ILoggingBuilder AddMyConsoleLogger(
            this ILoggingBuilder builder, Action<MyLoggerOptions> action)
        {
            MyLoggerOptions options = new();
            if (action != null)
            {
                action.Invoke(options);
            }

            builder.AddConfiguration();
            builder.Services.TryAddEnumerable(
                ServiceDescriptor.Singleton<ILoggerProvider>(new MyLoggerProvider(options)));
            return builder;
        }
    }

最后使用 Microsoft.Extensions.Logging 中的 LoggerFactory，构建日志工厂，从中生成 ILogger 对象，最后打印日志：

        static void Main(string[] args)
        {
            using ILoggerFactory factory = LoggerFactory.Create(builder =>
            {
                builder.AddConsole();
                builder.AddMyConsoleLogger(options =>
                {
                    options.DefaultLevel = LogLevel.Debug;
                });
            });
            ILogger logger1 = factory.CreateLogger("Program");
            ILogger logger2 = factory.CreateLogger<Program>();

            logger1.LogError(new Exception("报错了"), message: "Hello World! Logging is {Description}.", args: "error");
            logger2.LogError(new Exception("报错了"), message: "Hello World! Logging is {Description}.", args: "error");
        }