设计个性化、灵活、实时更新的配置管理器

这里所说的个性化、灵活、实时更新的定义？

个性化，是指你可以随意定义自己想要的配置结构、保存格式、存放位置等等。

灵活，是指可以方便的对配置进行读、写操作，并可以很容易实现任意多个配置管理器。

实时更新，是指在配置发生改变时可以实时的更新，且不会重启Web应用程序。

下面开始讲解设计。既然是配置管理器，那还是先定义好接口吧，请看IFileConfigManager<T>：

/// <summary>
/// Interface containing all properties and methods to be implemented
/// by file configuration manager.
/// </summary>
/// <typeparam name="T">The type of config entity.</typeparam>
public interface IFileConfigManager<T> : IDisposable 
    where T : class, new()
{
    /// <summary>
    /// Gets the path of the config file.
    /// </summary>
    string Path { get; }
 
    /// <summary>
    /// Gets the encoding to read or write the config file.
    /// </summary>
    Encoding Encoding { get; }
 
    /// <summary>
    /// Gets the serializer of the config manager for loading or saving the config file.
    /// </summary>
    FileConfigSerializer<T> Serializer { get; }
 
    /// <summary>
    /// Gets the current config entity.
    /// </summary>
    /// <returns></returns>
    T GetConfig();
 
    /// <summary>
    /// Saves the current config entity to file.
    /// </summary>
    void SaveConfig();
 
    /// <summary>
    /// Saves a specified config entity to file.
    /// </summary>
    /// <param name="config"></param>
    void SaveConfig(T config);
 
    /// <summary>
    /// Backups the current config entity to a specified path.
    /// </summary>
    /// <param name="backupPath"></param>
    void BackupConfig(string backupPath);
 
    /// <summary>
    /// Restores config entity from a specified path and saves to the current path.
    /// </summary>
    /// <param name="restorePath"></param>
    void RestoreConfig(string restorePath);
}

T参数当然就是定义的配置类型了，而且必须是引用类型，有无参数构造函数。Path是配置文件的完整路径，Encoding是读取和保存配置时用的编码，Serializer是处理配置序列化和反序列化的具体实现，GetConfig()是获取当前配置，SaveConfig()是保存当前配置，SaveConfig(T config)是保存指定的配置，BackupConfig(string backupPath)备份配置到指定路径，RestoreConfig(string restorePath)从指定路径还原配置。

接口IFileConfigManager<T>中定义的Serializer是用于支持自定义配置序列化功能的，下面看看FileConfigSerializer<T>的实现：

public abstract class FileConfigSerializer<T> 
    where T : class, new()
{
    #region Fields
 
    // XML格式
    public static readonly FileConfigSerializer<T> Xml = new XmlFileConfigSerializer();
 
    // 二进制格式
    public static readonly FileConfigSerializer<T> Binary = new BinaryFileConfigSerializer();
 
    #endregion
 
    #region Methods
 
    // 从配置文件反序列化，使用指定的编码
    public abstract T DeserializeFromFile(string path, Encoding encoding);
 
    // 序列化到配置文件，使用指定的编码
    public abstract void SerializeToFile(T config, string path, Encoding encoding);
 
    #endregion
 
    #region XmlFileConfigSerializer
 
    // 实现默认的Xml序列化类
    private sealed class XmlFileConfigSerializer : FileConfigSerializer<T> 
    {
        public override T DeserializeFromFile(string path, Encoding encoding)
        {
            return SerializationUtil.DeserializeFromXmlFile<T>(path, encoding);
        }
 
        public override void SerializeToFile(T config, string path, Encoding encoding)
        {
            SerializationUtil.SerializeToXmlFile(config, path, encoding);
        }
    }
 
    #endregion
 
    #region BinaryFileConfigSerializer
 
    // 实现默认的二进制序列化类
    private sealed class BinaryFileConfigSerializer : FileConfigSerializer<T>
    {
        public override T DeserializeFromFile(string path, Encoding encoding)
        {
            return SerializationUtil.DeserializeFromBinaryFile<T>(path, encoding);
        }
 
        public override void SerializeToFile(T config, string path, Encoding encoding)
        {
            SerializationUtil.SerializeToBinaryFile(config, path, encoding);
        }
    }
 
    #endregion
}

FileConfigSerializer<T>定义为抽象类，是为了方便默认的使用和扩展，里面使用的SerializationUtil类，是本人为了方便写的一个简单的序列化助手类，相信大家对对象的序列化操作不会陌生了，无非使用了System.Xml.Serialization.XmlSerializer、System.Runtime.Serialization.Formatters.Binary.BinaryFormatter、System.Runtime.Serialization.Json.DataContractJsonSerializer和System.Runtime.Serialization.NetDataContractSerializer来处理。如果不想用它们，你还可以实现FileConfigSerializer<T>进行完全的自己定义配置的加载与保存方式。对于json序列化推荐大家使用http://www.codeplex.com/json/　。

好了，大家已经知道了接口的定义了，下面来讲讲实时更新配置功能有哪些方法可以实现。我们知道，如果利用Web.config来配置的话，第一：如果配置内容多而杂，那会很乱；第二：如果手动修改配置，会导致Web重启（而我们并不希望它重启），所以，如果要解决上面两点问题，我们就要思考点什么了。上面我提到了Discuz!论坛的.net开源版本里配置管理，它是使用Timer来定时查检配置是否有修改，如果有修改就重新加载的，恩，这是一个可行的方案。还有其它方法吗？必须是有的，只要你肯去思考，下面列出本人想到的几个比较容易想到的方案：

方法１：使用Timer（.net库里有三个timer，请自行选择），每隔一秒就查检一下配置文件修改时间，如果文件被修改了，正更新最后修改时间并重新加载配置内容；

方法２：使用System.IO.FileSystemWatcher，可以实时监控配置文件，一发生改变即重新加载配置内容；

方法３：使用System.Web.Caching.Cache，加上缓存依赖，文件更改后缓存会失效，同样可以实时重新加载配置内容。

这三种方法中，方法３是本人比较推荐的，因为它的开销最小，而且可以实时更新配置，实现起来也是最简单的。对于新手可能看到这还不知道实现，下面再贴出本人实现上面接口的四个类，一个是默认管理器类，没有实时更新的功能，其它三个就是实现上面三种方法的管理器类了。

internal class DefaultFileConfigManager<T> : DisposableObject, IFileConfigManager<T>
    where T : class, new()
{
    #region Fields
 
    private string path = null;
    private Func<string> pathCreator = null;
 
    #endregion
 
    #region Constructors
 
    public DefaultFileConfigManager(Func<string> pathCreator, FileConfigSerializer<T> serializer, Encoding encoding)
    {
        pathCreator.ThrowsIfNull("pathCreator");
        serializer.ThrowsIfNull("serializer");
 
        this.pathCreator = pathCreator;
        this.Encoding = encoding;
        this.Serializer = serializer;
        this.SyncRoot = new object();
        this.Config = null;
    }
 
    #endregion
 
    #region Properties
 
    public string Path
    {
        get
        {
            if (this.path == null)
            {
                string path = this.pathCreator();
 
                path.ThrowsIfNull("The path returned form pathCreator is null.");
 
                this.path = path;
                this.LazyInitialize();
            }
 
            return this.path;
        }
    }
 
    public Encoding Encoding
    {
        get;
        protected set;
    }
 
    public FileConfigSerializer<T> Serializer
    {
        get;
        protected set;
    }
 
    protected object SyncRoot
    {
        get;
        set;
    }
 
    protected virtual T Config
    {
        get;
        set;
    }
 
    #endregion
 
    #region Methods
 
    public virtual T GetConfig()
    {
        if (this.Config == null)
        {
            lock (this.SyncRoot)
            {
                if (this.Config == null)
                {
                    FileInfo file = new FileInfo(this.Path);
                    if (!file.Exists)
                    {
                        // make sure the existence of the config directory
                        if (!file.Directory.Exists)
                        {
                            file.Directory.Create();
                        }
                        // save the default config to file
                        this.Config = new T();
                        this.Serializer.SerializeToFile(this.Config, this.Path, this.Encoding);
                    }
                    else
                    {
                        // else, loads from the specified path
                        this.Config = this.Serializer.DeserializeFromFile(this.Path, this.Encoding);
                    }
                }
            }
        }
 
        return this.Config;
    }
 
    public void SaveConfig()
    {
        this.SaveConfig(this.GetConfig());
    }
 
    public virtual void SaveConfig(T config)
    {
        config.ThrowsIfNull("config");
 
        lock (this.SyncRoot)
        {
            FileInfo file = new FileInfo(this.Path);
 
            // make sure the existence of the config directory
            if (!file.Directory.Exists)
            {
                file.Directory.Create();
            }
 
            this.Config = config;
            this.Serializer.SerializeToFile(this.Config, this.Path, this.Encoding);
        }
    }
 
    public void BackupConfig(string backupPath)
    {
        backupPath.ThrowsIfNull("backupPath");
 
        T config = this.GetConfig();
        this.Serializer.SerializeToFile(config, backupPath, this.Encoding);
    }
 
    public void RestoreConfig(string restorePath)
    {
        restorePath.ThrowsIfNull("restorePath");
 
        T config = this.Serializer.DeserializeFromFile(restorePath, this.Encoding);
        this.SaveConfig(config);
    }
 
    // this method is provided to subclasses to initialize their data
    protected virtual void LazyInitialize()
    {
    }
 
    #endregion
}

internal sealed class FileConfigManagerWithTimer<T> : DefaultFileConfigManager<T>
    where T : class, new()
{
    private Timer timer = null;
    private DateTime lastWriteTime = DateTime.MinValue; // a flag to notify us of the change config
 
    public FileConfigManagerWithTimer(Func<string> pathCreator, FileConfigSerializer<T> serializer, Encoding encoding)
        : base(pathCreator, serializer, encoding)
    {
    }
 
    protected override void LazyInitialize()
    {
        base.LazyInitialize();
 
        // initializes the timer, with it's interval of 1000 milliseconds
        this.timer = new Timer(1000);
        this.timer.Enabled = true;
        this.timer.AutoReset = true;
        this.timer.Elapsed += new ElapsedEventHandler(Timer_Elapsed);
        this.timer.Start();
    }
 
    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            // disposes the timer
            this.timer.Dispose();
            this.timer = null;
        }
    }
 
    private void Timer_Elapsed(object sender, ElapsedEventArgs e)
    {
        if (!File.Exists(this.Path))
        {
            // the file has been deleted
            return;
        }
 
        var tempWriteTime = File.GetLastWriteTime(this.Path);
 
        // if equals to the initial value, update it and return
        if (this.lastWriteTime == DateTime.MinValue)
        {
            this.lastWriteTime = tempWriteTime;
            return;
        }
 
        // if no equals to new write time, update it and reload config
        if (this.lastWriteTime != tempWriteTime)
        {
            this.lastWriteTime = tempWriteTime;
 
            lock (this.SyncRoot)
            {
                this.Config = this.Serializer.DeserializeFromFile(this.Path, this.Encoding);
            }
        }
    }
}

internal sealed class FileConfigManagerWithFileWatcher<T> : DefaultFileConfigManager<T>
    where T : class, new()
{
    private FileWatcher watcher = null;
 
    public FileConfigManagerWithFileWatcher(Func<string> pathCreator, FileConfigSerializer<T> serializer, Encoding encoding)
        : base(pathCreator, serializer, encoding)
    {
    }
 
    protected override void LazyInitialize()
    {
        base.LazyInitialize();
 
        // when the path is created, the watcher should be initialize at the same time
        watcher = new FileWatcher(this.Path, FileChanged);
        // just start watching the file
        watcher.StartWatching();
    }
 
    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            // disposes the watcher
            this.watcher.Dispose();
            this.watcher = null;
        }
 
        base.Dispose(disposing);
    }
 
    private void FileChanged(object sender, FileSystemEventArgs args)
    {
        lock (this.SyncRoot)
        {
            this.watcher.StopWatching();
            try
            {
                // note: here making the cuurent thread sleeping a litle while to avoid exception throwed by watcher
                Thread.Sleep(10);
                // reload the config from file
                this.Config = this.Serializer.DeserializeFromFile(this.Path, this.Encoding);
            }
            catch (Exception)
            {
                // ignore it
            }
            finally
            {
                this.watcher.StartWatching();
            }
        }
    }
}

internal sealed class FileConfigManagerWithCacheDependency<T> : DefaultFileConfigManager<T>
    where T : class, new()
{
    const string KeyPrefix = "FileConfig:";
 
    public FileConfigManagerWithCacheDependency(Func<string> pathCreator, FileConfigSerializer<T> serializer, Encoding encoding)
        : base(pathCreator, serializer, encoding)
    {
    }
 
    protected override T Config
    {
        get
        {
            return HttpRuntime.Cache[KeyPrefix + this.Path] as T;
        }
        set
        {
            // if not null, update the cache value
            if (value != null)
            {
                HttpRuntime.Cache.Insert(KeyPrefix + this.Path, value, new CacheDependency(this.Path), DateTime.