微软常用的组件设计思想-‘工厂的工厂类’

我们在写代码的时候，经常碰到各种软件的设计思想，也许，你是一个弱小的码农，也逃不了设计的思想已悄悄的走向你的身边，只是我们不知道这叫啥罢了。

诸如，我们经常玩的三层BLL DAL UI 那么还有一个东东，就是工厂Factory起到桥接作用。

回忆起三层，Factory 是一种设计模式

工厂方法模式的结构图如下：

Product定义了工厂方法所创建的对象的接口。
ConcreteProduct实现Product接口, 定义了具体对象。
Creator定义了具体对象创建的工厂方法，该方法返回一个Product类型的对象。Creator也可以定义一个工厂方法的缺省实现，它返回一个缺省的ConcreteProduct对象
ConcreteCreator实现Creator接口，重定义工厂方法以返回一个ConcreteProduct实例。
示例
我们以实现一个文档处理系统来看一下工厂方法模式的应用。
首先定义文档类型的接口和两个具体的文档类型

 1     public interface IFile
 2     {
 3         void New();
 4         void Save();
 5     } 
 6     public class DocFile : IFile
 7     {
 8         public void New()
 9         {
10             Console.WriteLine("New Doc Create");
11         }
12         public void Save()
13         {
14             Console.WriteLine("Save Doc");
15         }
16     }
17     public class TxtFile : IFile
18     {
19         public void New()
20         {
21             Console.WriteLine("New Txt Create");
22         }
23         public void Save()
24         {
25             Console.WriteLine("Save Txt");
26         }
27     }

接着实现对象创建的工厂方法及具体文档的创建工厂

 1     interface IFileFactory
 2     {
 3         IFile Create();
 4     }
 5     public class DocFileFactory : IFileFactory
 6     {
 7         public IFile Create()
 8         {
 9             return new DocFile();
10         }
11     }
12     public class TxtFileFactory : IFileFactory
13     {
14         public IFile Create()
15         {
16             return new TxtFile();
17         }
18     }

最后看一下如何调用

 1     static void Main(string[] args)
 2     {
 3         IFile docFile = (new DocFileFactory()).Create();
 4         docFile.New();
 5         docFile.Save();
 6         IFile txtFile = (new TxtFileFactory()).Create();
 7         txtFile.New();
 8         txtFile.Save();
 9         Console.ReadLine();
10     } 

回忆到此，想必，大家对工厂有个很好的体会了，不过，今天，我们看看微软是如何在工厂的基础上动手脚的

上图是微软最喜欢用的工厂设计模式思想(此例为日志工厂)。

我们来分析上面的思路

1）为了能够使程序在加载的时候，动态适应改变不同的工厂，而引入了LoggerFactory工厂类

2）减轻了每次在代码中去重复的指定工厂实现类

3）上图中，第一步通过LoggerFactory工厂类SetCurrent()指定当前工厂实现类TraceSourceLogFactory

4) LoggerFactory工厂类调用方法CreateLog()直接调用TraceSourceLogFactory工厂类Create(),进而创建出TraceSourceLog 现实类

我们来看看具体的代码：

1）ILogger接口：

   public interface ILogger
    {
        /// <summary>
        /// Log debug message
        /// </summary>
        /// <param name="message">The debug message</param>
        /// <param name="args">the message argument values</param>
        void Debug(string message, params object[] args);

        /// <summary>
        /// Log debug message
        /// </summary>
        /// <param name="message">The message</param>
        /// <param name="exception">Exception to write in debug message</param>
        void Debug(string message,Exception exception,params object[] args);

        /// <summary>
        /// Log debug message 
        /// </summary>
        /// <param name="item">The item with information to write in debug</param>
        void Debug(object item);

        /// <summary>
        /// Log FATAL error
        /// </summary>
        /// <param name="message">The message of fatal error</param>
        /// <param name="args">The argument values of message</param>
        void Fatal(string message, params object[] args);

        /// <summary>
        /// log FATAL error
        /// </summary>
        /// <param name="message">The message of fatal error</param>
        /// <param name="exception">The exception to write in this fatal message</param>
        void Fatal(string message, Exception exception,params object[] args);

        /// <summary>
        /// Log message information 
        /// </summary>
        /// <param name="message">The information message to write</param>
        /// <param name="args">The arguments values</param>
        void LogInfo(string message, params object[] args);

        /// <summary>
        /// Log warning message
        /// </summary>
        /// <param name="message">The warning message to write</param>
        /// <param name="args">The argument values</param>
        void LogWarning(string message, params object[] args);

        /// <summary>
        /// Log error message
        /// </summary>
        /// <param name="message">The error message to write</param>
        /// <param name="args">The arguments values</param>
        void LogError(string message, params object[] args);

        /// <summary>
        /// Log error message
        /// </summary>
        /// <param name="message">The error message to write</param>
        /// <param name="exception">The exception associated with this error</param>
        /// <param name="args">The arguments values</param>
        void LogError(string message, Exception exception, params object[] args);
    }

2)日志接口TraceSourceLog实现类：

 public sealed class TraceSourceLog
        :ILogger
    {
        #region Members

        TraceSource source;

        #endregion

        #region  Constructor

        /// <summary>
        /// Create a new instance of this trace manager
        /// </summary>
        public TraceSourceLog()
        {
            // Create default source
            source = new TraceSource("NLayerApp");
        }

        #endregion


        #region Private Methods

        /// <summary>
        /// Trace internal message in configured listeners
        /// </summary>
        /// <param name="eventType">Event type to trace</param>
        /// <param name="message">Message of event</param>
        void TraceInternal(TraceEventType eventType, string message)
        {

            if (source != null)
            {
                try
                {
                    source.TraceEvent(eventType, (int)eventType, message);
                }
                catch (SecurityException)
                {
                    //Cannot access to file listener or cannot have
                    //privileges to write in event log etc...
                }
            }
        }
        #endregion

        #region ILogger Members

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="args"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void LogInfo(string message, params object[] args)
        {
            if (!String.IsNullOrWhiteSpace(message))
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                TraceInternal(TraceEventType.Information, messageToTrace);
            }
        }
        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="args"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void LogWarning(string message, params object[] args)
        {

            if (!String.IsNullOrWhiteSpace(message))
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                TraceInternal(TraceEventType.Warning, messageToTrace);
            }
        }

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="args"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void LogError(string message, params object[] args)
        {
            if (!String.IsNullOrWhiteSpace(message))
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                TraceInternal(TraceEventType.Error, messageToTrace);
            }
        }

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="exception"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="args"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void LogError(string message, Exception exception, params object[] args)
        {
            if (!String.IsNullOrWhiteSpace(message)
                &&
                exception != null)
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                var exceptionData = exception.ToString(); // The ToString() create a string representation of the current exception

                TraceInternal(TraceEventType.Error, string.Format(CultureInfo.InvariantCulture, "{0} Exception:{1}", messageToTrace, exceptionData));
            }
        }

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="args"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void Debug(string message, params object[] args)
        {
            if (!String.IsNullOrWhiteSpace(message))
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                TraceInternal(TraceEventType.Verbose, messageToTrace);
            }
        }

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="exception"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="args"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void Debug(string message, Exception exception,params object[] args)
        {
            if (!String.IsNullOrWhiteSpace(message)
                &&
                exception != null)
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                var exceptionData = exception.ToString(); // The ToString() create a string representation of the current exception

                TraceInternal(TraceEventType.Error, string.Format(CultureInfo.InvariantCulture, "{0} Exception:{1}", messageToTrace, exceptionData));
            }
        }

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="item"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void Debug(object item)
        {
            if (item != null)
            {
                TraceInternal(TraceEventType.Verbose, item.ToString());
            }
        }

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="args"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void Fatal(string message, params object[] args)
        {
            if (!String.IsNullOrWhiteSpace(message))
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                TraceInternal(TraceEventType.Critical, messageToTrace);
            }
        }

        /// <summary>
        /// <see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/>
        /// </summary>
        /// <param name="message"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        /// <param name="exception"><see cref="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILogger"/></param>
        public void Fatal(string message, Exception exception,params object[] args)
        {
            if (!String.IsNullOrWhiteSpace(message)
                &&
                exception != null)
            {
                var messageToTrace = string.Format(CultureInfo.InvariantCulture, message, args);

                var exceptionData = exception.ToString(); // The ToString() create a string representation of the current exception

                TraceInternal(TraceEventType.Critical, string.Format(CultureInfo.InvariantCulture, "{0} Exception:{1}", messageToTrace, exceptionData));
            }
        }


        #endregion
    }

3) ILoggerFactory接口：

 /// <summary>
    /// Base contract for Log abstract factory
    /// </summary>
    public interface ILoggerFactory
    {
        /// <summary>
        /// Create a new ILog
        /// </summary>
        /// <returns>The ILog created</returns>
        ILogger Create();
    }

4）TraceSourceLogFactory 接口ILoggerFactory实现类

 /// <summary>
    /// A Trace Source base, log factory
    /// </summary>
    public class TraceSourceLogFactory
        :ILoggerFactory
    {
        /// <summary>
        /// Create the trace source log
        /// </summary>
        /// <returns>New ILog based on Trace Source infrastructure</returns>
        public ILogger Create()
        {
            return new TraceSourceLog();
        }
    }

5）LoggerFactory 工厂类

 /// <summary>
    /// Log Factory
    /// </summary>
    public static class LoggerFactory
    {
        #region Members

        static ILoggerFactory _currentLogFactory = null;

        #endregion

        #region Public Methods

        /// <summary>
        /// Set the  log factory to use
        /// </summary>
        /// <param name="logFactory">Log factory to use</param>
        public static void SetCurrent(ILoggerFactory logFactory)
        {
            _currentLogFactory = logFactory;
        }

        /// <summary>
        /// Createt a new <paramref name="Microsoft.Samples.NLayerApp.Infrastructure.Crosscutting.Logging.ILog"/>
        /// </summary>
        /// <returns>Created ILog</returns>
        public static ILogger CreateLog()
        {
            return (_currentLogFactory != null) ? _currentLogFactory.Create() : null;
        }

        #endregion
    }

在全局的项目配置里加入设置当前工厂方法

细心的朋友可以看出，下面还有其它类似的工厂，哈哈，换汤不换药。

调用：  LoggerFactory.CreateLog().LogError(Messages.error_CannotPerformTransferInvalidAccounts);

小结：设计的思想，就是从人的思想角度出发，驱动代码的构造。好的设计思想，往往都是从代码中提炼而来，从而推动了更优秀的设计思想，不断的创新迭出！

做为程序员多看看优质的源码，可以快速的吸收别人的精髓，这也是一种‘智取’。

作者：谷歌's（谷歌's博客园）
出处：http://www.cnblogs.com/laogu2/ 欢迎转载，但任何转载必须保留完整文章，在显要地方显示署名以及原文链接。如您有任何疑问或者授权方面的协商，请给我留言。