乐在其中设计模式(C#) - 提供者模式(Provider Pattern)
作者： 介绍 为一个API进行定义和实现的分离。 示例 有一个Message实体类，对它的操作有Insert()和Get()方法，持久化数据在SqlServer数据库中或Xml文件里。根据配置文件中的配置来决定数据持久化方案是使用SqlServer数据库还是Xml文件。 
MessageModel 
using System; namespace Pattern.Provider
{ 
/**//// <summary>
/// Message实体类
/// </summary> public class MessageModel { /**//// <summary> /// 构造函数 /// </summary> /// <param name="msg">Message内容</param> /// <param name="pt">Message发布时间</param> public MessageModel(string msg, DateTime pt) { this._message = msg; this._publishTime = pt; } private string _message; /**//// <summary> /// Message内容 /// </summary> public string Message { get { return _message; } set { _message = value; } } private DateTime _publishTime; /**//// <summary> /// Message发布时间 /// </summary> public DateTime PublishTime { get { return _publishTime; } set { _publishTime = value; } } }
} using System.Configuration.Provider; using System.Collections.Generic; namespace Pattern.Provider { /**//// <summary> /// 操作Message抽象类 /// </summary> public abstract class MessageProvider : ProviderBase { /**//// <summary> /// 插入Message /// </summary> /// <param name="mm">Message实体对象</param> /// <returns></returns> public abstract bool Insert(MessageModel mm); /**//// <summary> /// 获得Message /// </summary> /// <returns></returns> public abstract List<MessageModel> Get(); }} using System; using System.Collections.Specialized; using System.Collections.Generic; using System.Configuration.Provider; using System.Configuration; namespace Pattern.Provider { /**//// <summary> /// Sql方式操作Message /// </summary> public class SqlMessageProvider : MessageProvider { private string _connectionString; /**//// <summary> /// 插入Message /// </summary> /// <param name="mm">Message实体对象</param> /// <returns></returns> public override bool Insert(MessageModel mm) { // 代码略 return true; } /**//// <summary> /// 获取Message /// </summary> /// <returns></returns> public override List<MessageModel> Get() { List<MessageModel> l = new List<MessageModel>(); l.Add(new MessageModel("SQL方式，连接字符串是" + this._connectionString, DateTime.Now)); return l; } /**//// <summary> /// 初始化提供程序。 /// </summary> /// <param name="name">该提供程序的友好名称。</param> /// <param name="config">名称/值对的集合，表示在配置中为该提供程序指定的、提供程序特定的属性。</param> public override void Initialize(string name, NameValueCollection config) { if (string.IsNullOrEmpty(name)) name = "MessageProvider"; if (null == config) throw new ArgumentException("config参数不能为null"); if (string.IsNullOrEmpty(config["description"])) { config.Remove("description"); config.Add("description", "SqlServer操作Message"); } base.Initialize(name, config); string temp = config["connectionStringName"]; if (temp == null || temp.Length < 1) throw new ProviderException("connectionStringName属性缺少或为空"); _connectionString = ConfigurationManager.ConnectionStrings[temp].ConnectionString; if (_connectionString == null || _connectionString.Length < 1) { throw new ProviderException("没找到'" + temp + "'所指的连接字符串，或所指连接字符串为空"); } config.Remove("connectionStringName"); } }} using System; using System.Collections.Specialized; using System.Collections.Generic; using System.Configuration.Provider; using System.Configuration; namespace Pattern.Provider { /**//// <summary> /// Xmll方式操作Message /// </summary> public class XmlMessageProvider : MessageProvider { private string _connectionString; /**//// <summary> /// 插入Message /// </summary> /// <param name="mm">Message实体对象</param> /// <returns></returns> public override bool Insert(MessageModel mm) { // 代码略 return true; } /**//// <summary> /// 获取Message /// </summary> /// <returns></returns> public override List<MessageModel> Get() { List<MessageModel> l = new List<MessageModel>(); l.Add(new MessageModel("XML方式，连接字符串是" + this._connectionString, DateTime.Now)); return l; } /**//// <summary> /// 初始化提供程序。 /// </summary> /// <param name="name">该提供程序的友好名称。</param> /// <param name="config">名称/值对的集合，表示在配置中为该提供程序指定的、提供程序特定的属性。</param> public override void Initialize(string name, NameValueCollection config) { if (string.IsNullOrEmpty(name)) name = "MessageProvider"; if (null == config) throw new ArgumentException("config参数不能为null"); if (string.IsNullOrEmpty(config["description"])) { config.Remove("description"); config.Add("description", "XML操作Message"); } base.Initialize(name, config); string temp = config["connectionStringName"]; if (temp == null || temp.Length < 1) throw new ProviderException("connectionStringName属性缺少或为空"); _connectionString = ConfigurationManager.ConnectionStrings[temp].ConnectionString; if (_connectionString == null || _connectionString.Length < 1) { throw new ProviderException("没找到'" + temp + "'所指的连接字符串，或所指连接字符串为空"); } config.Remove("connectionStringName"); } }} using System.Configuration.Provider; using System; namespace Pattern.Provider { /**//// <summary> /// Message的Provider集合类 /// </summary> public class MessageProviderCollection : ProviderCollection { /**//// <summary> /// 向集合中添加提供程序。 /// </summary> /// <param name="provider">要添加的提供程序。</param> public override void Add(ProviderBase provider) { if (provider == null) throw new ArgumentNullException("provider参数不能为null"); if (!(provider is MessageProvider)) throw new ArgumentException("provider参数类型必须是MessageProvider."); base.Add(provider); } }} using System.Configuration; namespace Pattern.Provider { /**//// <summary> /// Message的Provider的配置 /// </summary> public class MessageProviderConfigurationSection : ConfigurationSection { private readonly ConfigurationProperty _defaultProvider; private readonly ConfigurationProperty _providers; private ConfigurationPropertyCollection _properties; /**//// <summary> /// 构造函数 /// </summary> public MessageProviderConfigurationSection() { _defaultProvider = new ConfigurationProperty("defaultProvider", typeof(string), null); _providers = new ConfigurationProperty("providers", typeof(ProviderSettingsCollection), null); _properties = new ConfigurationPropertyCollection(); _properties.Add(_providers); _properties.Add(_defaultProvider); } /**//// <summary> /// Message的默认的Provider /// </summary> [ConfigurationProperty("defaultProvider")] public string DefaultProvider { get { return (string)base[_defaultProvider]; } set { base[_defaultProvider] = value; } } /**//// <summary> /// Message的所有的Provider集合 /// </summary> [ConfigurationProperty("providers", DefaultValue = "SqlMessageProvider")] [StringValidator(MinLength = 1)] public ProviderSettingsCollection Providers { get { return (ProviderSettingsCollection)base[_providers]; } } /**//// <summary> /// Message的Provider的属性集合 /// </summary> protected override ConfigurationPropertyCollection Properties { get { return _properties; } } }} using System; using System.Collections.Generic; using System.Configuration; using System.Web.Configuration; namespace Pattern.Provider { /**//// <summary> /// 暴露给客户端用的Message的类（Context） /// </summary> public class Message { private static bool m_isInitialized = false; private static MessageProviderCollection _providers = null; private static MessageProvider _provider = null; /**//// <summary> /// 静态构造函数，初始化 /// </summary> static Message() { Initialize(); } /**//// <summary> /// 插入信息 /// </summary> /// <param name="mm">Message实体对象</param> /// <returns></returns> public static bool Insert(MessageModel mm) { return _provider.Insert(mm); } /**//// <summary> /// 获取信息 /// </summary> /// <returns></returns> public static List<MessageModel> Get() { return _provider.Get(); } private static void Initialize() { try { MessageProviderConfigurationSection messageConfig = null; if (!m_isInitialized) { // 找到配置文件中“MessageProvider”节点 messageConfig = (MessageProviderConfigurationSection)ConfigurationManager.GetSection("MessageProvider"); if (messageConfig == null) throw new ConfigurationErrorsException("在配置文件中没找到“MessageProvider”节点"); _providers = new MessageProviderCollection(); // 使用System.Web.Configuration.ProvidersHelper类调用每个Provider的Initialize()方法 ProvidersHelper.InstantiateProviders(messageConfig.Providers, _providers, typeof(MessageProvider)); // 所用的Provider为配置中默认的Provider _provider = _providers[messageConfig.DefaultProvider] as MessageProvider; m_isInitialized = true; } } catch (Exception ex) { string msg = ex.Message; throw new Exception(msg); } } private static MessageProvider Provider { get { return _provider; } } private static MessageProviderCollection Providers { get { return _providers; } } }} 
<? xml version="1.0" encoding="utf-8" ?> < configuration > < configSections > < section name ="MessageProvider" type ="Pattern.Provider.MessageProviderConfigurationSection, Pattern.Provider" /> </ configSections > < MessageProvider defaultProvider ="SqlMessageProvider" > < providers > < add name ="XmlMessageProvider" type ="Pattern.Provider.XmlMessageProvider, Pattern.Provider" connectionStringName ="XmlConnection" /> < add name ="SqlMessageProvider" type ="Pattern.Provider.SqlMessageProvider, Pattern.Provider" connectionStringName ="SqlConnection" /> </ providers > </ MessageProvider > < connectionStrings > < add name ="SqlConnection" connectionString ="server=.;database=db;uid=sa;pwd=sa" /> < add name ="XmlConnection" connectionString ="XmlPath" /> </ connectionStrings > </ configuration > using System; using System.Data; using System.Configuration; using System.Collections; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; using Pattern.Provider; public partial class Provider : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { Response.Write(Message.Insert(new MessageModel("插入", DateTime.Now))); Response.Write("<br />"); Response.Write(Message.Get()[0].Message + " " + Message.Get()[0].PublishTime.ToString()); }}