[asp.net 5] Logging-日志系統的基本架構（上）

本節主要介紹解決方案中的Microsoft.Framework.Logging.Abstractions、Microsoft.Framework.Logging倆個工程。

這倆個工程中所有類的關系如下圖所示：

首先我們可以發現處于核心的是中間的四個接口：ILogger、ILoggerFactory、ILoggerPRovider、ILogValues。

• ILogger：記錄日志的接口，所以寫日志的類都該實現該接口，工程中有倆個類實現了該接口：Logger、Logger<T>
• ILoggerFactory：創建ILogger的工廠。負責創建工廠的邏輯，但是一般不直接創建，而是調用內部ILoggerProvider去完成。
• ILoggerProvider：能夠直接創建ILogger實例，做為屬性添加到ILoggerFactory中，ILogger的具體邏輯受控制ILoggerFactory。
• ILogValues：在Logger的擴展方法中作為特殊類型的object傳入，作為日志的數據源。

接口的定義源碼如下：

    public interface ILogger    {        void Log(LogLevel logLevel, int eventId, object state, Exception exception, Func<object, Exception, string> formatter);        bool IsEnabled(LogLevel logLevel);                IDisposable BeginScopeImpl(object state);    }

    public interface ILoggerFactory    {        LogLevel MinimumLevel { get; set; }        ILogger CreateLogger(string categoryName);        void AddProvider(ILoggerProvider provider);    }

    public interface ILoggerProvider    {        ILogger CreateLogger(string name);    }

    public interface ILogValues    {        IEnumerable<KeyValuePair<string, object>> GetValues();    }

ILogger以及實現類

ILogger接口、ILogger<TCategoryName>（沒有任何定義）、Logger<T>這種泛型繼承是否有相識之感，之前的博客文章中已經對于這種情況有所介紹（[Asp.net 5] Localization-resx資源文件的管理中IStringLocalizer 、IStringLocalizer<T> 、StringLocalizer<TResourceSource>是一致的）。實際Logger<T>中T是ILogger的實例子類，實際就是使用代理模式，內部包含ILogger實例，并且所有對外的方法都僅僅是內部ILogger實例的封裝。

    public class Logger<T> : ILogger<T>    {        private readonly ILogger _logger;                /// <summary>        /// Creates a new <see cref="Logger{T}"/>.        /// </summary>        /// <param name="factory">The factory.</param>        public Logger(ILoggerFactory factory)        {            _logger = factory.CreateLogger<T>();        }        IDisposable ILogger.BeginScopeImpl(object state)        {            return _logger.BeginScopeImpl(state);        }        bool ILogger.IsEnabled(LogLevel logLevel)        {            return _logger.IsEnabled(logLevel);        }        void ILogger.Log(LogLevel logLevel, int eventId, object state, Exception exception, Func<object, Exception, string> formatter)        {            _logger.Log(logLevel, eventId, state, exception, formatter);        }    }

Logger類同樣實現了ILogger接口，也同樣使用了代理模式，不過不同于Logger<T>泛型，Logger類有自己的內部邏輯。而是在內部封裝了ILogger[] _loggers對象。使得Logger更像LoggerManage。但是由于Logger同樣實現Logger接口，所以Logger類是管理其它Logger類的代理。而Logger內部的_loggers是通過LoggerFactory對象封裝的。當記錄日志時，依次遍歷內部的_loggers對象，進行寫日志操作。

    internal class Logger : ILogger    {        private readonly LoggerFactory _loggerFactory;        private readonly string _name;        private ILogger[] _loggers = new ILogger[0];        public Logger(LoggerFactory loggerFactory, string name)        {            _loggerFactory = loggerFactory;            _name = name;            var providers = loggerFactory.GetProviders();            _loggers = new ILogger[providers.Length];            for (var index = 0; index != providers.Length; index++)            {                _loggers[index] = providers[index].CreateLogger(name);            }        }        public void Log(LogLevel logLevel, int eventId, object state, Exception exception, Func<object, Exception, string> formatter)        {            if (logLevel >= _loggerFactory.MinimumLevel)            {                foreach (var logger in _loggers)                {                    logger.Log(logLevel, eventId, state, exception, formatter);                }            }        }        public bool IsEnabled(LogLevel logLevel)        {            if (logLevel < _loggerFactory.MinimumLevel)            {                return false;            }            foreach (var logger in _loggers)            {                if (logger.IsEnabled(logLevel))                {                    return true;                }            }            return false;        }        public IDisposable BeginScopeImpl(object state)        {            var loggers = _loggers;            var scope = new Scope(loggers.Length);            for (var index = 0; index != loggers.Length; index++)            {                scope.SetDisposable(index, loggers[index].BeginScopeImpl(state));            }            return scope;        }        internal void AddProvider(ILoggerProvider provider)        {            var logger = provider.CreateLogger(_name);            _loggers = _loggers.Concat(new[] { logger }).ToArray();        }        private class Scope : IDisposable        {            private bool _isDisposed;            private IDisposable _disposable0;            private IDisposable _disposable1;            private readonly IDisposable[] _disposable;            public Scope(int count)            {                if (count > 2)                {                    _disposable = new IDisposable[count - 2];                }            }            public void SetDisposable(int index, IDisposable disposable)            {                if (index == 0)                {                    _disposable0 = disposable;                }                else if (index == 1)                {                    _disposable1 = disposable;                }                else                {                    _disposable[index - 2] = disposable;                }            }            protected virtual void Dispose(bool disposing)            {