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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);
????????}
????????/**////?<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
[源码下载]??
（编辑：李大同）
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