白话ASP.NET MVC之三：Controller是如何解析出来的

我们在上一篇文章中介绍Controller激活系统中所涉及到的一些类型，比如有关Controller类型的相关定义类型就包括了IController类型，IAsyncController类型，ControllerBase抽象类型和我们最终要使用的抽象类型Controller，这是ASP.NET MVC 框架中和Controller本身定义相关的类型。其他辅助类型，包括管理Controller的类型ControllerFactory，这个工厂负责Controller的生产和销毁。我们还涉及到另一个辅助类型，用于把系统默认定义的或者自定义的ControllerFactory注册到ASP.NET MVC框架中的类型ControllerBuilder。

Controller类型、ControllerFactory类型和ControllerBuilder类型，他们之间的关系可以描述为：ControllerBuilder是面向客户的，或者说是程序员和ASP.NET MVC框架之间的桥梁。我们通过ControllerBuilder类型的SetControllerFactory方法把我们自定义的ControllerFactory类型实例注册到ASP.NET MVC框架中，ControllerFactory类型用于管理Controller类型实例，其实也就是说ControllerFactory类型就是ASP.NET MVC框架中的一个扩展点。

我们今天主要讲Controller是怎么解析出来的，之所以把这一部分分开写，因为合在一起太长了，也说的不详细，如果大家对以上说的不太清楚，可以查看《白话ASP.NET MVC之二：Controller激活系统的概览》，  该文对ASP.NET MVC框架中所提到的Controlelr激活系统所涉及的类型有详细的介绍。

一、“路由系统”和“激活系统”是怎么关联起来的

上一篇文章有过讲述，我们在这里简单说一下。ASP.NET 的路由系统是建立在一个叫做UrlRoutingModule的HttpModule组件上的，针对请求的路由解析是通过注册HttpApplication对象的PostResolveRequestCache事件来实现的，为当前的请求动态映射到一个HttpHandler类型上，最终由该HttpHandler接管请求并处理。我们来看看UrlRoutingModule类型的代码吧。

 public class UrlRoutingModule : IHttpModule
 {
     private static readonly object _contextKey = new object();

     private static readonly object _requestDataKey = new object();

     private RouteCollection _routeCollection;

     public RouteCollection RouteCollection
     {
         get
         {
             if (this._routeCollection == null)
             {
                 this._routeCollection = RouteTable.Routes;
             }
             return this._routeCollection;
         }
         set
         {
             this._routeCollection = value;
         }
     }

     protected virtual void Dispose()
     {
     }

     protected virtual void Init(HttpApplication application)
     {
         if (application.Context.Items[UrlRoutingModule._contextKey] != null)
         {
             return;
         }
             application.Context.Items[UrlRoutingModule._contextKey] = UrlRoutingModule._contextKey;
         application.PostResolveRequestCache += new EventHandler(this.OnApplicationPostResolveRequestCache);
     }

     private void OnApplicationPostResolveRequestCache(object sender, EventArgs e)
     {
         HttpContextBase context = new HttpContextWrapper(((HttpApplication)sender).Context);
             this.PostResolveRequestCache(context);
     }

     [Obsolete("This method is obsolete. Override the Init method to use the PostMapRequestHandler event.")]
         public virtual void PostMapRequestHandler(HttpContextBase context)
     {
     }

     public virtual void PostResolveRequestCache(HttpContextBase context)
     {
         RouteData routeData = this.RouteCollection.GetRouteData(context);
         if (routeData == null)
         {
             return;
         }
         IRouteHandler routeHandler = routeData.RouteHandler;
         if (routeHandler == null)
         {
             ]));
         }
         if (routeHandler is StopRoutingHandler)
         {
             return;
         }
         RequestContext requestContext = new RequestContext(context, routeData);
         context.Request.RequestContext = requestContext;
         IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);
         if (httpHandler == null)
         {
             throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, SR.GetString("UrlRoutingModule_NoHttpHandler"), new object[]
             {
                 routeHandler.GetType()
             }));
         }
         if (!(httpHandler is UrlAuthFailureHandler))
         {
             context.RemapHandler(httpHandler);
             return;
         }
         if (FormsAuthenticationModule.FormsAuthRequired)
         {
                 UrlAuthorizationModule.ReportUrlAuthorizationFailure(HttpContext.Current, this);
             return;
         }
         , SR.GetString("Assess_Denied_Description3"));
     }

     void IHttpModule.Dispose()
     {
             this.Dispose();
     }

     void IHttpModule.Init(HttpApplication application)
     {
             this.Init(application);
     }
 }

具体来说，该组件通过以RouteTable的静态属性Routes表示的路由表针对当前请求实施路由解析，如果有匹配，就会根据路由对象Route来生成RouteData路由数据对象，然后我们借助RouteData对象的RouteHandler属性获取想要的HttpHandler对象。在默认情况下这个RouteHandler属性所代表的对象是MvcRouteHandler。翠花，上代码：

 /// <summary>Creates an object that implements the IHttpHandler interface and passes the request context to it.</summary>
 public class MvcRouteHandler : IRouteHandler
 {
     private IControllerFactory _controllerFactory;

     /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.MvcRouteHandler" /> class.</summary>
     public MvcRouteHandler()
     {
     }

     /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.MvcRouteHandler" /> class using the specified factory controller object.</summary>
     /// <param name="controllerFactory">The controller factory.</param>
     public MvcRouteHandler(IControllerFactory controllerFactory)
     {
         this._controllerFactory = controllerFactory;
     }

     /// <summary>Returns the HTTP handler by using the specified HTTP context.</summary>
     /// <returns>The HTTP handler.</returns>
     /// <param name="requestContext">The request context.</param>
     protected virtual IHttpHandler GetHttpHandler(RequestContext requestContext)
     {
         requestContext.HttpContext.SetSessionStateBehavior(this.GetSessionStateBehavior(requestContext));
         return new MvcHandler(requestContext);
     }

     /// <summary>Returns the session behavior.</summary>
     /// <returns>The session behavior.</returns>
     /// <param name="requestContext">The request context.</param>
     protected virtual SessionStateBehavior GetSessionStateBehavior(RequestContext requestContext)
     {
         string text = (string)requestContext.RouteData.Values["controller"];
         if (string.IsNullOrWhiteSpace(text))
         {
             throw new InvalidOperationException(MvcResources.MvcRouteHandler_RouteValuesHasNoController);
         }
         IControllerFactory controllerFactory = this._controllerFactory ?? ControllerBuilder.Current.GetControllerFactory();
         return controllerFactory.GetControllerSessionBehavior(requestContext, text);
     }

     /// <summary>Returns the HTTP handler by using the specified request context.</summary>
     /// <returns>The HTTP handler.</returns>
     /// <param name="requestContext">The request context.</param>
     IHttpHandler IRouteHandler.GetHttpHandler(RequestContext requestContext)
     {
         return this.GetHttpHandler(requestContext);
     }
 }

在该类型里面包含了一个IControllerFactory类型成员字段，这个接口类型是所有ControllerFactory都要必须实现的接口，否则就不叫Controller的工厂了。MvcRouteHandler类型有两个构造函数，无参的没的说，另一个需要传递一个IControllerFactory类型的参数，这个参数用于初始化MvcRouteHandler类型内部包含的类型为IControllerFactory的_controllerFactory字段。当我们构造MvcRouteHandler实例的时候，如果我们调用了无参的构造函数，它会在内部使用ControllerBuilder.Current.GetControllerFactory（）方法来获取我们通过ControllerBuilder类型注册的IControllerFactory类型的实例，代码很明显：

IControllerFactory controllerFactory = this._controllerFactory ?? ControllerBuilder.Current.GetControllerFactory();

MvcRouteHandler实现了IRouteHandler接口，目的只有一个，提供后续的HttpHandler，IRouteHandler接口定义如下：

 public interface IRouteHandler
 {
     IHttpHandler GetHttpHandler(RequestContext requestContext);
 }

MvcRouteHandler会给我们直接返回MvcHandler对象，这个对象用于处理请求，包括激活Controler对象，代码最有说服力，这份代码，上篇文章也贴过，现在也贴一下把，上代码：

 /// <summary>Selects the controller that will handle an HTTP request.</summary>
 public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
 {
     private struct ProcessRequestState
     {
         internal IAsyncController AsyncController;

         internal IControllerFactory Factory;

         internal RequestContext RequestContext;

         internal void ReleaseController()
         {
                 this.Factory.ReleaseController(this.AsyncController);
         }
     }

     private static readonly object _processRequestTag = new object();

     internal static readonly string MvcVersion = MvcHandler.GetMvcVersionString();

     /// <summary>Contains the header name of the ASP.NET MVC version.</summary>
     public static readonly string MvcVersionHeaderName = "X-AspNetMvc-Version";

     private ControllerBuilder _controllerBuilder;

     internal ControllerBuilder ControllerBuilder
     {
         get
         {
             if (this._controllerBuilder == null)
             {
                 this._controllerBuilder = ControllerBuilder.Current;
             }
             return this._controllerBuilder;
         }
         set
         {
             this._controllerBuilder = value;
         }
     }

     /// <summary>Gets or sets a value that indicates whether the MVC response header is disabled.</summary>
     /// <returns>true if the MVC response header is disabled; otherwise, false.</returns>
     public static bool DisableMvcResponseHeader
     {
         get;
         set;
     }

     /// <summary>Gets a value that indicates whether another request can use the <see cref="T:System.Web.IHttpHandler" /> instance.</summary>
     /// <returns>true if the <see cref="T:System.Web.IHttpHandler" /> instance is reusable; otherwise, false.</returns>
     protected virtual bool IsReusable
     {
         get
         {
             return false;
         }
     }

     /// <summary>Gets the request context.</summary>
     /// <returns>The request context.</returns>
     public RequestContext RequestContext
     {
         get;
         private set;
     }

     /// <summary>Gets a value that indicates whether another request can use the <see cref="T:System.Web.IHttpHandler" /> instance.</summary>
     /// <returns>true if the <see cref="T:System.Web.IHttpHandler" /> instance is reusable; otherwise, false.</returns>
     bool IHttpHandler.IsReusable
     {
         get
         {
             return this.IsReusable;
         }
     }

     /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.MvcHandler" /> class.</summary>
     /// <param name="requestContext">The request context.</param>
     /// <exception cref="T:System.ArgumentNullException">The <paramref name="requestContext" /> parameter is null.</exception>
     public MvcHandler(RequestContext requestContext)
     {
         if (requestContext == null)
         {
             throw new ArgumentNullException("requestContext");
         }
         this.RequestContext = requestContext;
     }

     /// <summary>Adds the version header by using the specified HTTP context.</summary>
     /// <param name="httpContext">The HTTP context.</param>
     protected internal virtual void AddVersionHeader(HttpContextBase httpContext)
     {
         if (!MvcHandler.DisableMvcResponseHeader)
         {
             httpContext.Response.AppendHeader(MvcHandler.MvcVersionHeaderName, MvcHandler.MvcVersion);
         }
     }

     /// <summary>Called by ASP.NET to begin asynchronous request processing.</summary>
     /// <returns>The status of the asynchronous call.</returns>
     /// <param name="httpContext">The HTTP context.</param>
     /// <param name="callback">The asynchronous callback method.</param>
     /// <param name="state">The state of the asynchronous object.</param>
     protected virtual IAsyncResult BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, object state)
     {
         HttpContextBase httpContext2 = new HttpContextWrapper(httpContext);
         return this.BeginProcessRequest(httpContext2, callback, state);
     }

     /// <summary>Called by ASP.NET to begin asynchronous request processing using the base HTTP context.</summary>
     /// <returns>The status of the asynchronous call.</returns>
     /// <param name="httpContext">The HTTP context.</param>
     /// <param name="callback">The asynchronous callback method.</param>
     /// <param name="state">The state of the asynchronous object.</param>
     protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state)
     {
         IController controller;
         IControllerFactory factory;
         this.ProcessRequestInit(httpContext, out controller, out factory);
         IAsyncController asyncController = controller as IAsyncController;
         if (asyncController != null)
         {
             BeginInvokeDelegate<MvcHandler.ProcessRequestState> beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState, MvcHandler.ProcessRequestState innerState)
             {
                 IAsyncResult result;
                 try
                 {
                     result = innerState.AsyncController.BeginExecute(innerState.RequestContext, asyncCallback, asyncState);
                 }
                 catch
                 {
                     innerState.ReleaseController();
                     throw;
                 }
                 return result;
             };
             EndInvokeVoidDelegate<MvcHandler.ProcessRequestState> endDelegate = delegate(IAsyncResult asyncResult, MvcHandler.ProcessRequestState innerState)
             {
                 try
                 {
                     innerState.AsyncController.EndExecute(asyncResult);
                 }
                 finally
                 {
                     innerState.ReleaseController();
                 }
                 ;
                 MvcHandler.ProcessRequestState invokeState = new MvcHandler.ProcessRequestState
                 {
                     AsyncController = asyncController,
                     Factory = factory,
                     RequestContext = this.RequestContext
                 };
                 SynchronizationContext synchronizationContext = SynchronizationContextUtil.GetSynchronizationContext();
                 , synchronizationContext);
             }
             Action action = delegate
             {
                 try
                 {
                     controller.Execute(this.RequestContext);
                 }
                 finally
                 {
                     factory.ReleaseController(controller);
                 }
             };
             return AsyncResultWrapper.BeginSynchronous(callback, state, action, MvcHandler._processRequestTag);
         }

         /// <summary>Called by ASP.NET when asynchronous request processing has ended.</summary>
         /// <param name="asyncResult">The asynchronous result.</param>
         protected internal virtual void EndProcessRequest(IAsyncResult asyncResult)
         {
             AsyncResultWrapper.End(asyncResult, MvcHandler._processRequestTag);
         }

         private static string GetMvcVersionString()
         {
             );
         }

         /// <summary>Processes the request by using the specified HTTP request context.</summary>
         /// <param name="httpContext">The HTTP context.</param>
         protected virtual void ProcessRequest(HttpContext httpContext)
         {
             HttpContextBase httpContext2 = new HttpContextWrapper(httpContext);
             this.ProcessRequest(httpContext2);
         }

         /// <summary>Processes the request by using the specified base HTTP request context.</summary>
         /// <param name="httpContext">The HTTP context.</param>
         protected internal virtual void ProcessRequest(HttpContextBase httpContext)
         {
             IController controller;
             IControllerFactory controllerFactory;
             this.ProcessRequestInit(httpContext, out controller, out controllerFactory);
             try
             {
                 controller.Execute(this.RequestContext);
             }
             finally
             {
                 controllerFactory.ReleaseController(controller);
             }
     }

     private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
     {
         HttpContext current = HttpContext.Current;
         if (current != null && ValidationUtility.IsValidationEnabled(current) == true)
             {                ValidationUtility.EnableDynamicValidation(current);
             }            this.AddVersionHeader(httpContext);
             this.RemoveOptionalRoutingParameters();
             string requiredString = this.RequestContext.RouteData.GetRequiredString("controller");
             factory = this.ControllerBuilder.GetControllerFactory();
             controller = factory.CreateController(this.RequestContext, requiredString);
             if (controller == null)
             {
                 throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_FactoryReturnedNull, new object[]
                 {
                     factory.GetType(),
                     requiredString
                 }));
             }
         }

         private void RemoveOptionalRoutingParameters()
         {
             RouteValueDictionary values = this.RequestContext.RouteData.Values;
             values.RemoveFromDictionary((KeyValuePair<string, object> entry) => entry.Value == UrlParameter.Optional);
         }

         /// <summary>Enables processing of HTTP Web requests by a custom HTTP handler that implements the <see cref="T:System.Web.IHttpHandler" /> interface.</summary>
         /// <param name="httpContext">An <see cref="T:System.Web.HttpContext" /> object that provides references to the intrinsic server objects (for example, Request, Response, Session, and Server) that are used to service HTTP requests.</param>
         void IHttpHandler.ProcessRequest(HttpContext httpContext)
         {
             this.ProcessRequest(httpContext);
         }

         /// <summary>Called by ASP.NET to begin asynchronous request processing using the base HTTP context.</summary>
         /// <returns>The status of the asynchronous call.</returns>
         /// <param name="context">The HTTP context.</param>
         /// <param name="cb">The asynchronous callback method.</param>
         /// <param name="extraData">The data.</param>
         IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
         {
             return this.BeginProcessRequest(context, cb, extraData);
         }

         /// <summary>Called by ASP.NET when asynchronous request processing has ended.</summary>
         /// <param name="result">The asynchronous result.</param>
         void IHttpAsyncHandler.EndProcessRequest(IAsyncResult result)
         {
             this.EndProcessRequest(result);
         }
     }

MvcHandler类型的BeginProcessRequest方法用来处理请求，包括激活Controller实例等。由于MvcHandler类型同时实现了IHttpHandler接口和IHttpAsyncHandler接口，所以他总是异步方式去执行（调用BeginProcessRequest/EndProcessRequest方法）。BeginProcessRequest方法在执行的时候通过RequestContext对象的RouteData属性获得Controller的名字，然后在通过ControllerBuilder获得ControllerFactory对象，然后用Controller的名字和ControllerFactory对象来激活目标Controller实例。如果Controller类型实现了IAsyncController接口，那就以异步方式执行Controller，否则以同步方式执行。Controller对象成功执行后，MvcHandler对象会调用ControllerFactory对象ReleaseController方法来销毁Controller实例对象。

我们小结一下，ASP.NET MVC的路由系统和Controller的激活系统是通过这些对象关联起来的：请求Url ------->Route------->RouteData------->RouteHandler（MvcRouteHandler）-------->MvcRouteHandler------>MvcHandler，通过这些对象就能串起来了。

二、Controller的详细解析过程

我先来简述一下Controller解析的原理吧。Controller实例对象的解析是通过实现了IControllerFactory接口的ControllerFactory对象实现的，ControllerFactory是怎么来的呢？是通过调用ControllerBuilder的SetControllerFactory方法实现对ControllerFactory类型或者实例对象的注册。如果我们没有调用ControllerBuilder的SetControllerFactory方法对象ControllerFactory类型或者实例显示注册，系统会使用默认的ControllerFactory来完成对Controller对象的解析，这个对象就是DefaultControllerFactory类型，该类型的实现正好反映了ASP.NET MVC框架对Controller实例的激活采取的默认策略。今天我们就看看DefaultControllerFactory类型是如何把Controller对象激活的，这也是Controller激活系统的默认实现，我们可以扩展ControllerFactory类型，实现自定义的Controller激活策略。

我把代码流程写一下，在MvcHandler类型里面有两个方法，一个方法是：BeginProcessRequest（HttpContextBase httpContext,AsyncCallback callback,object state），该方法用于对请求进行处理；第二个方法是：ProcessRequestInit(HttpContextbase httpContext,out IController controller,out IControllerFactory controllerFactory)，该方法就是定义了激活Controller算法的骨架，上代码吧，代码最无二意，我们先看BeginProcessRequest的代码：

     protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state)
     {
         IController controller;
         IControllerFactory factory;
         this.ProcessRequestInit(httpContext, out controller, out factory);
         IAsyncController asyncController = controller as IAsyncController;
         if (asyncController != null)
         {
                 BeginInvokeDelegate<MvcHandler.ProcessRequestState> beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState, MvcHandler.ProcessRequestState innerState)
             {
                 IAsyncResult result;
                 try
                 {
                     result = innerState.AsyncController.BeginExecute(innerState.RequestContext, asyncCallback, asyncState);
                 }
                 catch
                 {
                     innerState.ReleaseController();
                     throw;
                 }
                 return result;
             };
                 EndInvokeVoidDelegate<MvcHandler.ProcessRequestState> endDelegate = delegate(IAsyncResult asyncResult, MvcHandler.ProcessRequestState innerState)
             {
                 try
                 {
                     innerState.AsyncController.EndExecute(asyncResult);
                 }
                 finally
                 {
                     innerState.ReleaseController();
                 }
             };
             MvcHandler.ProcessRequestState invokeState = new MvcHandler.ProcessRequestState
             {
                 AsyncController = asyncController,
                 Factory = factory,
                 RequestContext = this.RequestContext
             };
             SynchronizationContext synchronizationContext = SynchronizationContextUtil.GetSynchronizationContext();
             , synchronizationContext);
         }
         Action action = delegate
         {
             try
             {
                 controller.Execute(this.RequestContext);
             }
             finally
             {
                 factory.ReleaseController(controller);
             }
         };
         return AsyncResultWrapper.BeginSynchronous(callback, state, action, MvcHandler._processRequestTag);
     }

在这个方法里面根据解析出来的Controller的类型来执行，如果是异步的Controller那就异步执行，否则就同步执行。在该方法里面，第三行，标红色的方法就是定义解析和执行Controller的算法骨架，就是我们要贴代码的第二个方法ProcessRequestInit，源码如下：

     private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
     {
         HttpContext current = HttpContext.Current;
         if (current != null && ValidationUtility.IsValidationEnabled(current) == true)
         {
                 ValidationUtility.EnableDynamicValidation(current);
         }
         this.AddVersionHeader(httpContext);
         this.RemoveOptionalRoutingParameters();
         string requiredString = this.RequestContext.RouteData.GetRequiredString("controller");
11         factory = this.ControllerBuilder.GetControllerFactory();
12         controller = factory.CreateController(this.RequestContext, requiredString);
         if (controller == null)
         {
             throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_FactoryReturnedNull, new object[]
             {
                 factory.GetType(),
                 requiredString
             }));
         }
     }

这个方法主要是获取ControllerFactory实例，根据获得的ControllerFactory对象激活Controller对象，红色标注的代码就是核心关键点。说明一点，这个方法只是定义了激活Controller算法的骨架，具体的实现在DefaultControllerFactory类型中。代码很简单，我相信大家看的清楚。

DefaultControllerFactory通过调用BuildManager的静态方法GetReferencedAssemblies获取到系统所使用到的所有程序集，然后针对每个程序集通过反射的方式获得所有实现了IController接口的类型，并保存起来。然后我们把Controller的名称和命名空间作为匹配条件去查找对应的Controller类型。当我们获得了符合标准的真是的Controller类型后，DefaultControllerFactory对象通过反射的方式创建Controller类型的实例对象。解析逻辑不复杂，但是代码不少。我把完整的源码贴出来，大家可以仔细体会一下。

 /// <summary>Represents the controller factory that is registered by default.</summary>
     public class DefaultControllerFactory : IControllerFactory
     {
         private class DefaultControllerActivator : IControllerActivator
         {
             private Func<IDependencyResolver> _resolverThunk;

             public DefaultControllerActivator() : this(null)
             {
             }

             public DefaultControllerActivator(IDependencyResolver resolver)
             {
                 if (resolver == null)
                 {
                     this._resolverThunk = (() => DependencyResolver.Current);
                     return;
                 }
                 this._resolverThunk = (() => resolver);
             }

             public IController Create(RequestContext requestContext, Type controllerType)
             {
                 IController result;
                 try
                 {
                     result = (IController)(this._resolverThunk().GetService(controllerType) ?? Activator.CreateInstance(controllerType));
                 }
                 catch (Exception innerException)
                 {
                     throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ErrorCreatingController, new object[]
                     {
                         controllerType
                     }), innerException);
                 }
                 return result;
             }
         }

         private static readonly ConcurrentDictionary<Type, SessionStateBehavior> _sessionStateCache = new ConcurrentDictionary<Type, SessionStateBehavior>();

         private static ControllerTypeCache _staticControllerTypeCache = new ControllerTypeCache();

         private IBuildManager _buildManager;

         private IResolver<IControllerActivator> _activatorResolver;

         private IControllerActivator _controllerActivator;

         private ControllerBuilder _controllerBuilder;

         private ControllerTypeCache _instanceControllerTypeCache;

         private IControllerActivator ControllerActivator
         {
             get
             {
                 if (this._controllerActivator != null)
                 {
                     return this._controllerActivator;
                 }
                 this._controllerActivator = this._activatorResolver.Current;
                 return this._controllerActivator;
             }
         }

         internal IBuildManager BuildManager
         {
             get
             {
                 if (this._buildManager == null)
                 {
                     this._buildManager = new BuildManagerWrapper();
                 }
                 return this._buildManager;
             }
             set
             {
                 this._buildManager = value;
             }
         }

         internal ControllerBuilder ControllerBuilder
         {
             get
             {
                 return this._controllerBuilder ?? ControllerBuilder.Current;
             }
             set
             {
                 this._controllerBuilder = value;
             }
         }

         internal ControllerTypeCache ControllerTypeCache
         {
             get
             {
                 return this._instanceControllerTypeCache ?? DefaultControllerFactory._staticControllerTypeCache;
             }
             set
             {
                 this._instanceControllerTypeCache = value;
             }
         }

         /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.DefaultControllerFactory" /> class.</summary>
         public DefaultControllerFactory() : this(null, null, null)
         {
         }

         /// <summary>Initializes a new instance of the <see cref="T:System.Web.Mvc.DefaultControllerFactory" /> class using a controller activator.</summary>
         /// <param name="controllerActivator">An object that implements the controller activator interface.</param>
         public DefaultControllerFactory(IControllerActivator controllerActivator) : this(controllerActivator, null, null)
         {
         }

         internal DefaultControllerFactory(IControllerActivator controllerActivator, IResolver<IControllerActivator> activatorResolver, IDependencyResolver dependencyResolver)
         {
             if (controllerActivator != null)
             {
                 this._controllerActivator = controllerActivator;
                 return;
             }
             IResolver<IControllerActivator> arg_44_1 = activatorResolver;
             if (activatorResolver == null)
             {
                 arg_44_1 = new SingleServiceResolver<IControllerActivator>(() => null, new DefaultControllerFactory.DefaultControllerActivator(dependencyResolver), "DefaultControllerFactory constructor");
             }
             this._activatorResolver = arg_44_1;
         }

         internal static InvalidOperationException CreateAmbiguousControllerException(RouteBase route, string controllerName, ICollection<Type> matchingTypes)
         {
             StringBuilder stringBuilder = new StringBuilder();
             foreach (Type current in matchingTypes)
             {
                 stringBuilder.AppendLine();
                 stringBuilder.Append(current.FullName);
             }
             Route route2 = route as Route;
             string message;
             if (route2 != null)
             {
                 message = string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ControllerNameAmbiguous_WithRouteUrl, new object[]
                 {
                     controllerName,
                     route2.Url,
                     stringBuilder,
                     Environment.NewLine
                 });
             }
             else
             {
                 message = string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ControllerNameAmbiguous_WithoutRouteUrl, new object[]
                 {
                     controllerName,
                     stringBuilder,
                     Environment.NewLine
                 });
             }
             return new InvalidOperationException(message);
         }

         private static InvalidOperationException CreateDirectRouteAmbiguousControllerException(ICollection<Type> matchingTypes)
         {
             StringBuilder stringBuilder = new StringBuilder();
             foreach (Type current in matchingTypes)
             {
                 stringBuilder.AppendLine();
                 stringBuilder.Append(current.FullName);
             }
             string message = string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_DirectRouteAmbiguous, new object[]
             {
                 stringBuilder,
                 Environment.NewLine
             });
             return new InvalidOperationException(message);
         }

         /// <summary>Creates the specified controller by using the specified request context.</summary>
         /// <returns>The controller.</returns>
         /// <param name="requestContext">The context of the HTTP request, which includes the HTTP context and route data.</param>
         /// <param name="controllerName">The name of the controller.</param>
         /// <exception cref="T:System.ArgumentNullException">The <paramref name="requestContext" /> parameter is null.</exception>
         /// <exception cref="T:System.ArgumentException">The <paramref name="controllerName" /> parameter is null or empty.</exception>
         public virtual IController CreateController(RequestContext requestContext, string controllerName)
         {
             if (requestContext == null)
             {
                 throw new ArgumentNullException("requestContext");
             }
             if (string.IsNullOrEmpty(controllerName) && !requestContext.RouteData.HasDirectRouteMatch())
             {
                 throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
             }
             Type controllerType = this.GetControllerType(requestContext, controllerName);
             return this.GetControllerInstance(requestContext, controllerType);
         }

         /// <summary>Retrieves the controller instance for the specified request context and controller type.</summary>
         /// <returns>The controller instance.</returns>
         /// <param name="requestContext">The context of the HTTP request, which includes the HTTP context and route data.</param>
         /// <param name="controllerType">The type of the controller.</param>
         /// <exception cref="T:System.Web.HttpException">
         ///   <paramref name="controllerType" /> is null.</exception>
         /// <exception cref="T:System.ArgumentException">
         ///   <paramref name="controllerType" /> cannot be assigned.</exception>
         /// <exception cref="T:System.InvalidOperationException">An instance of <paramref name="controllerType" /> cannot be created.</exception>
         protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType)
         {
             if (controllerType == null)
             {
                 , string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_NoControllerFound, new object[]
                 {
                     requestContext.HttpContext.Request.Path
                 }));
             }
             if (!typeof(IController).IsAssignableFrom(controllerType))
             {
                 throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_TypeDoesNotSubclassControllerBase, new object[]
                 {
                     controllerType
                 }), "controllerType");
             }
             return this.ControllerActivator.Create(requestContext, controllerType);
         }

         /// <summary>Returns the controller's session behavior.</summary>
         /// <returns>The controller's session behavior.</returns>
         /// <param name="requestContext">The request context.</param>
         /// <param name="controllerType">The type of the controller.</param>
         protected internal virtual SessionStateBehavior GetControllerSessionBehavior(RequestContext requestContext, Type controllerType)
         {
             if (controllerType == null)
             {
                 return SessionStateBehavior.Default;
             }
             return DefaultControllerFactory._sessionStateCache.GetOrAdd(controllerType, delegate(Type type)
             {
                 SessionStateAttribute sessionStateAttribute = type.GetCustomAttributes(typeof(SessionStateAttribute), true).OfType<SessionStateAttribute>().FirstOrDefault<SessionStateAttribute>();
                 if (sessionStateAttribute == null)
                 {
                     return SessionStateBehavior.Default;
                 }
                 return sessionStateAttribute.Behavior;
             });
         }

         /// <summary>Retrieves the controller type for the specified name and request context.</summary>
         /// <returns>The controller type.</returns>
         /// <param name="requestContext">The context of the HTTP request, which includes the HTTP context and route data.</param>
         /// <param name="controllerName">The name of the controller.</param>
         protected internal virtual Type GetControllerType(RequestContext requestContext, string controllerName)
         {
             if (requestContext == null)
             {
                 throw new ArgumentNullException("requestContext");
             }
             if (string.IsNullOrEmpty(controllerName) && (requestContext.RouteData == null || !requestContext.RouteData.HasDirectRouteMatch()))
             {
                 throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
             }
             RouteData routeData = requestContext.RouteData;
             if (routeData != null && routeData.HasDirectRouteMatch())
             {
                 return DefaultControllerFactory.GetControllerTypeFromDirectRoute(routeData);
             }
             object obj;
             if (routeData.DataTokens.TryGetValue("Namespaces", out obj))
             {
                 IEnumerable<string> enumerable = obj as IEnumerable<string>;
                 if (enumerable != null && enumerable.Any<string>())
                 {
                     HashSet<string> namespaces = new HashSet<string>(enumerable, StringComparer.OrdinalIgnoreCase);
                     Type controllerTypeWithinNamespaces = this.GetControllerTypeWithinNamespaces(routeData.Route, controllerName, namespaces);
                     if (controllerTypeWithinNamespaces != null || false.Equals(routeData.DataTokens["UseNamespaceFallback"]))
                     {
                         return controllerTypeWithinNamespaces;
                     }
                 }
             }
             )
             {
                 HashSet<string> namespaces2 = new HashSet<string>(this.ControllerBuilder.DefaultNamespaces, StringComparer.OrdinalIgnoreCase);
                 Type controllerTypeWithinNamespaces = this.GetControllerTypeWithinNamespaces(routeData.Route, controllerName, namespaces2);
                 if (controllerTypeWithinNamespaces != null)
                 {
                     return controllerTypeWithinNamespaces;
                 }
             }
             return this.GetControllerTypeWithinNamespaces(routeData.Route, controllerName, null);
         }

         private static Type GetControllerTypeFromDirectRoute(RouteData routeData)
         {
             IEnumerable<RouteData> directRouteMatches = routeData.GetDirectRouteMatches();
             List<Type> list = new List<Type>();
             foreach (RouteData current in directRouteMatches)
             {
                 if (current != null)
                 {
                     Type targetControllerType = current.GetTargetControllerType();
                     if (targetControllerType == null)
                     {
                         throw new InvalidOperationException(MvcResources.DirectRoute_MissingControllerType);
                     }
                     if (!list.Contains(targetControllerType))
                     {
                         list.Add(targetControllerType);
                     }
                 }
             }
             )
             {
                 return null;
             }
             )
             {
                 ];
             }
             throw DefaultControllerFactory.CreateDirectRouteAmbiguousControllerException(list);
         }

         private Type GetControllerTypeWithinNamespaces(RouteBase route, string controllerName, HashSet<string> namespaces)
         {
             this.ControllerTypeCache.EnsureInitialized(this.BuildManager);
             ICollection<Type> controllerTypes = this.ControllerTypeCache.GetControllerTypes(controllerName, namespaces);
             switch (controllerTypes.Count)
             {
             :
                 return null;
             :
                 return controllerTypes.First<Type>();
             default:
                 throw DefaultControllerFactory.CreateAmbiguousControllerException(route, controllerName, controllerTypes);
             }
         }

         /// <summary>Releases the specified controller.</summary>
         /// <param name="controller">The controller to release.</param>
         public virtual void ReleaseController(IController controller)
         {
             IDisposable disposable = controller as IDisposable;
             if (disposable != null)
             {
                 disposable.Dispose();
             }
         }

         internal IReadOnlyList<Type> GetControllerTypes()
         {
             this.ControllerTypeCache.EnsureInitialized(this.BuildManager);
             return this.ControllerTypeCache.GetControllerTypes();
         }

         /// <summary>This API supports the ASP.NET MVC infrastructure and is not intended to be used directly from your code. This method calls the <see cref="M:System.Web.Mvc.DefaultControllerFactory.GetControllerSessionBehavior(System.Web.Routing.RequestContext,System.Type)" /> method.</summary>
         /// <returns>The controller's session behavior.</returns>
         /// <param name="requestContext">The request context.</param>
         /// <param name="controllerName">The controller name.</param>
         SessionStateBehavior IControllerFactory.GetControllerSessionBehavior(RequestContext requestContext, string controllerName)
         {
             if (requestContext == null)
             {
                 throw new ArgumentNullException("requestContext");
             }
             if (string.IsNullOrEmpty(controllerName))
             {
                 throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
             }
             Type controllerType = this.GetControllerType(requestContext, controllerName);
             return this.GetControllerSessionBehavior(requestContext, controllerType);
         }
     }

既然是ControllerFactory，DefaultControllerFactory肯定也实现了IControllerFactory接口，别的我们就不看了，我们看看是如何创建Controller对象的，方法代码如下：

 public virtual IController CreateController(RequestContext requestContext, string controllerName)
 {
     if (requestContext == null)
     {
         throw new ArgumentNullException("requestContext");
     }
     if (string.IsNullOrEmpty(controllerName) && !requestContext.RouteData.HasDirectRouteMatch())
     {
         throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
     }
     Type controllerType = this.GetControllerType(requestContext, controllerName);
     return this.GetControllerInstance(requestContext, controllerType);
 }

代码很简单，该方法获取Controller的Type类型对象，然后根据Type对象创建实例。这个方法里面有两个辅助方法，一个是GetControllerType方法，另一个是GetControllerInstance方法，根据名称我们就能知道是做什么的。我们先看看GetControllerType方法的源码吧，这里是关键，没有Type对象的获取，以后都是空言：　　

 protected internal virtual Type GetControllerType(RequestContext requestContext, string controllerName)
 {
     if (requestContext == null)
     {
         throw new ArgumentNullException("requestContext");
     }
     if (string.IsNullOrEmpty(controllerName) && (requestContext.RouteData == null || !requestContext.RouteData.HasDirectRouteMatch()))
     {
         throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
     }
     RouteData routeData = requestContext.RouteData;
     if (routeData != null && routeData.HasDirectRouteMatch())
     {
         return DefaultControllerFactory.GetControllerTypeFromDirectRoute(routeData);
     }
     object obj;
     if (routeData.DataTokens.TryGetValue("Namespaces", out obj))
     {
         IEnumerable<string> enumerable = obj as IEnumerable<string>;
         if (enumerable != null && enumerable.Any<string>())
         {
             HashSet<string> namespaces = new HashSet<string>(enumerable, StringComparer.OrdinalIgnoreCase);
             Type controllerTypeWithinNamespaces = this.GetControllerTypeWithinNamespaces(routeData.Route, controllerName, namespaces);
             if (controllerTypeWithinNamespaces != null || false.Equals(routeData.DataTokens["UseNamespaceFallback"]))
             {
                 return controllerTypeWithinNamespaces;
             }
         }
     }
     )
     {
         HashSet<string> namespaces2 = new HashSet<string>(this.ControllerBuilder.DefaultNamespaces, StringComparer.OrdinalIgnoreCase);
         Type controllerTypeWithinNamespaces = this.GetControllerTypeWithinNamespaces(routeData.Route, controllerName, namespaces2);
         if (controllerTypeWithinNamespaces != null)
         {
             return controllerTypeWithinNamespaces;
         }
     }
     return this.GetControllerTypeWithinNamespaces(routeData.Route, controllerName, null);
 }

我们先根据RouteData路由数据来获取Controller的类型对象，如果RouteData不为空，并且在RouteData的Values属性中包含Key为“MS_DirectRouteMatches”的值，那我们就据此获取Controller的类型对象，如果没找到就返回Null值，如果有一个值，就会作为Controller的Type类型值返回，如果多于一个就会抛出异常。如果RouteData不包含Key为“MS_DirectRouteMatches”的值，我们就根据RouteData对象中DataTokens属性Key为“Namespaces”来获取Controller的Type对象，同理，如果没找到就返回null，找到一个就直接返回，如果多余一个的话就抛出异常。

如果我们还是没找到怎么办呢？我们就要看看能不能使用后备命名空间，如果可以，就根据此命名空间来查找，我们从RouteData路由数据的DataTokens属性中查找是否包含有Key为“UseNamespaceFallback”的值，如果有，并且是False，就直接返回，结束查找，如果不包含Key为“UseNamepsaceFallback”的值或者该值为True，我们就可以根据ControllerBuilder的DefaultNamespaces属性表示后备命名空间查找Controller的类型，同理，没有找到就返回null，找到一个就作为结果值直接返回，如果多于一个那就要抛出异常了。

好了，大概的逻辑写完了，

三、扩展点

      到了现在，Controller激活系统就写的差不多了，唯一还差一点的就是扩展点还没提。ASP.NET MVC号称几乎任何地方都可以扩展，Controller激活系统中肯定也包含着扩展点，下来我们一一详述。

四、小结

我们可以小结了，到此，Controler激活系统这个小节我就写完了。其实不是很复杂，大家在看的时候，刚开始别太关注代码的细节，先把握整个数据流向，或者叫请求脉络，把里面所涉及到的对象和关系都整理清楚了，然后再有针对性的去看涉及到的每个对象，不是画画图，不是画画，是画各个对象之间的关系图，图能画出来，说明你的心中就有了整体把握了。如果太关注细节，太关注某个类型的代码，也会很容易顾此失彼，因为我开始就是那样，总是看了后面忘记前面，请求的线路也不是很清楚。所以我们学习的时候也要有方法，方法对，学的就快，成就感就能很快产生。好了，说了这么多了，继续努力吧，希望我写的东西对大家有所帮助。