二十四种设计模式：提供者模式(Provider Pattern)
提供者模式(Provider Pattern)
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
<?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>
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
