设计模式 - Provider Pattern(提供者模式)

设计模式 - Provider Pattern(提供者模式)

作者： webabcd


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; }

        }

    }

}

MessageProvider

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();

    }

}

sqlMessageProvider

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");

        }

    }

}

XmlMessageProvider

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");

        }

    }

}

MessageProviderCollection

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);

        }

    }

}

MessageProviderConfigurationSection

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);

        }

@H_404_3335@

        /**//// <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; }

        }

    }

}

Message

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;

            }

        }

    }

}

Web.config

< 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 >

Test

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());

    }

}

运行结果
True
sql方式，连接字符串是server=.;database=db;uid=sa;pwd=sa 2007-1-22 8:21:44

from:http://www.cnblogs.com/webabcd/archive/2007/01/22/626479.html
OK
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