.NET Core 读取配置文件方式总结

基于.NET Core的跨平台开发，配置文件与之前.NET Framework采用xml的config文件不同，目前主要是采用json文件键值对配置方式读取。

参考网上相关资料总结如下：

一、引入扩展 System.Configuration.ConfigurationManager

Nuget 下载扩展，Install-Package System.Configuration.ConfigurationManager

使用方式：添加配置文件App.config。读取方式与原.NET Framework方式一致

优点：兼容.NET Framework 原有配置方式

缺点：项目运行过程中若需修改App.config文件，对项目中输出的内容没有丝毫影响，Debug发现获取到的值的确没有变化，需要重新编译才生效。

二、引入扩展 Microsoft.Extensions.Options.ConfigurationExtensions

Nuget 下载扩展， 

Install-Package Microsoft.Extensions.Options.ConfigurationExtensions 

Install-Package Microsoft.Extensions.Configuration.FileExtensions

Install-Package Microsoft.Extensions.Configuration.Json

使用方式：参考微软官网：https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/configuration/index?view=aspnetcore-2.1&tabs=basicconfiguration

优点：可以读取application.json中的配置参数，不再使用XML可以说很好的贴近Core的设计理念

缺点：运行时修改json文件读取到的内容不会改变，但是至少重启项目可以修改，若要运行时候修改json文件监听实现监听变化。查看源码，可以发现 虽然配置信息是通过AddSingleton注入的
但同时也注入了IOptionsChangeTokenSource ，故只需要在获取配置信息时将IOptions<> 替换为 IOptionsMonitor<>(通过监听的Option来获取信息)，并通过 IOptionsMonitor<>.CurrentValue获取即可实时获取到最新的配置信息(存在修改监听)

另外就是，这个方法采用的是反序列化的原理，也就是必须有一个跟配置文件对应的实体类才可以，这个感觉比较鸡肋，放弃。

三、自定义扩展方法，这个实现自己写，原理是监听文件是否变更，来刷新Configuration 配置实现。

参考园友一个实现，具体需要是否有效，要花时间实践一下，原链接地址：http://www.cnblogs.com/kasimlz/p/7515810.html，代码如下：

public class ConfigurationManager
    {
        /// <summary>
        /// 配置内容
        /// </summary>
        private static NameValueCollection _configurationCollection = new NameValueCollection();

        /// <summary>
        /// 配置监听响应链堆栈
        /// </summary>
        private static Stack<KeyValuePair<string, FileSystemWatcher>> FileListeners = new Stack<KeyValuePair<string, FileSystemWatcher>>();

        /// <summary>
        /// 默认路径
        /// </summary>
        private static string _defaultPath = Directory.GetCurrentDirectory() + "\appsettings.json";

        /// <summary>
        /// 最终配置文件路径
        /// </summary>
        private static string _configPath = null;

        /// <summary>
        /// 配置节点关键字
        /// </summary>
        private static string _configSection = "AppSettings";

        /// <summary>
        /// 配置外连接的后缀
        /// </summary>
        private static string _configUrlPostfix = "Url";

        /// <summary>
        /// 最终修改时间戳
        /// </summary>
        private static long _timeStamp = 0L;

        /// <summary>
        /// 配置外链关键词，例如：AppSettings.Url
        /// </summary>
        private static string _configUrlSection { get { return _configSection + "." + _configUrlPostfix; } }


        static ConfigurationManager()
        {
            ConfigFinder(_defaultPath);
        }

        /// <summary>
        /// 确定配置文件路径
        /// </summary>
        private static void ConfigFinder(string Path)
        {
            _configPath = Path;
            JObject config_json = new JObject();
            while (config_json != null)
            {
                config_json = null;
                FileInfo config_info = new FileInfo(_configPath);
                if (!config_info.Exists) break;

                FileListeners.Push(CreateListener(config_info));
                config_json = LoadJsonFile(_configPath);
                if (config_json[_configUrlSection] != null)
                    _configPath = config_json[_configUrlSection].ToString();
                else break;
            }

            if (config_json == null || config_json[_configSection] == null) return;

            LoadConfiguration();
        }

        /// <summary>
        /// 读取配置文件内容
        /// </summary>
        private static void LoadConfiguration()
        {
            FileInfo config = new FileInfo(_configPath);
            var configColltion = new NameValueCollection();
            JObject config_object = LoadJsonFile(_configPath);
            if (config_object == null || !(config_object is JObject)) return;
           
            if (config_object[_configSection]!=null)
            {
                foreach (JProperty prop in config_object[_configSection])
                {
                    configColltion[prop.Name] = prop.Value.ToString();
                }
            }
            
            _configurationCollection = configColltion;
        }

        /// <summary>
        /// 解析Json文件
        /// </summary>
        /// <param name="FilePath">文件路径</param>
        /// <returns></returns>
        private static JObject LoadJsonFile(string FilePath)
        {
            JObject config_object = null;
            try
            {
                StreamReader sr = new StreamReader(FilePath, Encoding.Default);
                config_object = JObject.Parse(sr.ReadToEnd());
                sr.Close();
            }
            catch { }
            return config_object;
        }

        /// <summary>
        /// 添加监听树节点
        /// </summary>
        /// <param name="info"></param>
        /// <returns></returns>
        private static KeyValuePair<string, FileSystemWatcher> CreateListener(FileInfo info)
        {

            FileSystemWatcher watcher = new FileSystemWatcher();
            watcher.BeginInit();
            watcher.Path = info.DirectoryName;
            watcher.Filter = info.Name;
            watcher.IncludeSubdirectories = false;
            watcher.EnableRaisingEvents = true;
            watcher.NotifyFilter = NotifyFilters.Attributes | NotifyFilters.CreationTime | NotifyFilters.DirectoryName | NotifyFilters.FileName | NotifyFilters.LastAccess | NotifyFilters.LastWrite | NotifyFilters.Size;
            watcher.Changed += new FileSystemEventHandler(ConfigChangeListener);
            watcher.EndInit();

            return new KeyValuePair<string, FileSystemWatcher>(info.FullName, watcher);
          
        }

        private static void ConfigChangeListener(object sender, FileSystemEventArgs e)
        {
            long time = TimeStamp();
            lock (FileListeners)
            {
                if (time > _timeStamp)
                {
                    _timeStamp = time;
                    if (e.FullPath != _configPath || e.FullPath == _defaultPath)
                    {
                        while (FileListeners.Count > 0)
                        {
                            var listener = FileListeners.Pop();
                            listener.Value.Dispose();
                            if (listener.Key == e.FullPath) break;
                        }
                        ConfigFinder(e.FullPath);
                    }
                    else
                    {
                        LoadConfiguration();
                    }
                }
            }
        }

        private static long TimeStamp()
        {
            return (long)((DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds * 100);
        }

        private static string c_configSection = null;
        public static string ConfigSection
        {
            get { return _configSection; }
            set { c_configSection = value; }
        }


        private static string c_configUrlPostfix = null;
        public static string ConfigUrlPostfix
        {
            get { return _configUrlPostfix; }
            set { c_configUrlPostfix = value; }
        }

        private static string c_defaultPath = null;
        public static string DefaultPath
        {
            get { return _defaultPath; }
            set { c_defaultPath = value; }
        }

        public static NameValueCollection AppSettings
        {
            get { return _configurationCollection; }
        }

        /// <summary>
        /// 手动刷新配置，修改配置后，请手动调用此方法，以便更新配置参数
        /// </summary>
        public static void RefreshConfiguration()
        {
            lock (FileListeners)
            {
                //修改配置
                if (c_configSection != null) { _configSection = c_configSection; c_configSection = null; }
                if (c_configUrlPostfix != null) { _configUrlPostfix = c_configUrlPostfix; c_configUrlPostfix = null; }
                if (c_defaultPath != null) { _defaultPath = c_defaultPath; c_defaultPath = null; }
                //释放掉全部监听响应链
                while (FileListeners.Count > 0)
                    FileListeners.Pop().Value.Dispose();
                ConfigFinder(_defaultPath);
            }
        }

    }