Controller的创建

      在ASP.NET MVC 中所有的Controller类都直接或间接继承IController接口，所有的网页的Controller数据请求与响应处理的入口就是IController接口中的Execute方法，Execute方法只接收RequestContext参数，RequestContext参数中的RouteData是有关所请求路由的信息，里面包含了Controller，Action的名字等信息。HttpContext包含了HTTP 请求的信息。

      Controller的创建来源于IControllerFactory接口中的IController CreateController(RequestContext requestContext, string controllerName);

      当请求进入到MvcHandler类的ProcessRequest(HttpContext httpContext)方法钟就进行IControllerFactory，IController的创建;

  private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
  {
      HttpContext currentContext = HttpContext.Current;
      if (currentContext != null)
      { bool? isRequestValidationEnabled = ValidationUtility.IsValidationEnabled(currentContext);
        if (isRequestValidationEnabled == true)
        { ValidationUtility.EnableDynamicValidation(currentContext);}
      }
      AddVersionHeader(httpContext);//响应头里面加入MVC的版本号
      RemoveOptionalRoutingParameters();
      string controllerName = RequestContext.RouteData.GetRequiredString("controller");  // Get the controller type

      factory = ControllerBuilder.GetControllerFactory(); 
      controller = factory.CreateController(RequestContext, controllerName); 
 
       if (controller == null) 
       { throw new InvalidOperationException( String.Format( CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_FactoryReturnedNull, factory.GetType(), controllerName)        ); }
  }   

  public class ControllerBuilder
  {
     private static ControllerBuilder _instance = new ControllerBuilder();
     private Func<IControllerFactory> _factoryThunk = () => null;
     private HashSet<string> _namespaces = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
     private IResolver<IControllerFactory> _serviceResolver;
     public ControllerBuilder(): this(null)
     { }
     internal ControllerBuilder(IResolver<IControllerFactory> serviceResolver)
     {
        _serviceResolver = serviceResolver ?? new SingleServiceResolver<IControllerFactory>(
                                               () => _factoryThunk(),new DefaultControllerFactory { ControllerBuilder = this },"ControllerBuilder.GetControllerFactory");
     }

      public static ControllerBuilder Current
      {get { return _instance; }
       public IControllerFactory GetControllerFactory()
       {
          return _serviceResolver.Current;
       }//     设置指定的控制器工厂。
       public void SetControllerFactory(IControllerFactory controllerFactory);//     使用指定的类型来设置控制器工厂。
       public void SetControllerFactory(Type controllerFactoryType);
}

      从ProcessRequestInit代码中可以看到 IControllerFactory 来源于 ControllerBuilder.GetControllerFactory方法，ControllerBuilder类动态的生成构造器；ControllerBuilder类的构造函数中默认设置了DefaultControllerFactory 类作为IControllerFactory接口的实现类，我们也可以自己来实现IControllerFactory接口来，通过SetControllerFactory方法附件到ControllerBuilder类中；这样设计提高了框架的扩展性和灵活性；

      DefaultControllerFactory 类作为MVC框架中的 IControllerFactory接口的默认实现类，Controller也是通过这个类来进行创建；主要分两步，首先要获取 controller的类型，然后进行controller的构造；

   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 = GetControllerType(requestContext, controllerName);
      IController controller = GetControllerInstance(requestContext, controllerType);
       return controller;
    }

       在获取controller类型的过程中，首先判断RouteData的RouteValueDictionary中有没有默认的IControllerFactory类型，如果存在直接返回controllerType;由于不同的Controller存在不同的Namespaces中，因此获取controllerType首先获取Namespaces;获取Namespaces的顺序首先是RouteData中的DataTokens中key为“Namespaces”的数据，当上述情况不存在时，获取ControllerBuilder.DefaultNamespaces中的Namespaces列表，当二者的Namespaces都为空时，就进行整个应用程序的所有Namespaces进行全局搜索对应的controllerType；

     由于RouteData中的controllerName 是不区别大小写的，而C#的类名是区分大小写的，因此直接通过名字查找是行不通的，MVC 框架采用的是查找到所有的类型，然后根据这些类的名字去匹配controllerName；由于应用程序中含有大量DLL，含有大量的controller，因此MVC 框架采用了缓存机制；

  

  public void EnsureInitialized(IBuildManager buildManager)
  {
        if (_cache == null)
        {
          lock (_lockObj)
          {
            if (_cache == null)
             {
                 List<Type> controllerTypes = TypeCacheUtil.GetFilteredTypesFromAssemblies(TypeCacheName, IsControllerType, buildManager);
                 var groupedByName = controllerTypes.GroupBy( t => t.Name.Substring(0, t.Name.Length - "Controller".Length), StringComparer.OrdinalIgnoreCase);
                  _cache = groupedByName.ToDictionary( g => g.Key,
                                                      g => g.ToLookup(t => t.Namespace ?? String.Empty, StringComparer.OrdinalIgnoreCase),
                                                      StringComparer.OrdinalIgnoreCase);
              }
           }
        }
 }

       在 ControllerTypeCache类中的EnsureInitialized 构造了 Dictionary<string, ILookup<string, Type>>结构的缓存_cache ,Dictionary的key是控制器的名称（去掉“Controller”后缀),Value是Key为Namespace,Value为ControllerType;当查找ControllerType时，首先通过Controller查找，然后在进行Namespace匹配，提高了查询的效率；

      对于GetFilteredTypesFromAssemblies方法中的TypeCacheName参数是Cache的Name,在MVC中对于的值是"MVC-ControllerTypeCache.xml",IsControllerType是判断是否为ControllerType的委托方法（判断Type是否是抽象类，是否继承IController接口，是否是Controller结尾）,buildManager是管理 ASP.NET 应用程序编译的方法的类，缓存文件的读取/写入,加载应用程序的dll都是通过这个类的方法实现;

      对于_cache 缓存的地址是在HttpRuntime.CodegenDir+"//UserCache//MVC-ControllerTypeCache.xml"文件中；

<?xml version="1.0" encoding="utf-8"?>
<!--此文件自动生成。请不要修改此文件的内容。-->
<typeCache lastModified="2015-11-27 15:32:08" mvcVersionId="72d59038-e845-45b1-853a-70864614e003">
  <assembly name="ApplicationWeb, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
    <module versionId="a5615a50-9b2b-4ea3-8dbc-870592b04b35">
      <type>ApplicationWeb.Controllers.AccountController</type>
      <type>ApplicationWeb.Controllers.HomeController</type>
    </module>
  </assembly>
</typeCache>

　  当获取到控制器的Type后就可以进行ControllerType的创建，在DefaultControllerFactory类中对ControllerType的创建时通过IControllerActivator接口中的 IController Create(RequestContext requestContext, Type controllerType)来实现的;通过DefaultControllerFactory代码我们可以发现IControllerActivator接口的默认实现类时DefaultControllerActivator;DefaultControllerActivator类中的Create方法首先通DefaultDependencyResolver类中的GetService方法创建(内部也是调用的Activator.CreateInstance)方法；  

 private class DefaultControllerActivator : IControllerActivator
 {
     private Func<IDependencyResolver> _resolverThunk;
     public DefaultControllerActivator() : this(null)
     { }
     public DefaultControllerActivator(IDependencyResolver resolver)
     { 
  
        if (resolver == null)
        { _resolverThunk = () => DependencyResolver.Current;   }
        else
        {  _resolverThunk = () => resolver;  }
     }
     public IController Create(RequestContext requestContext, Type controllerType)
     {
        try
        {
            return (IController)(_resolverThunk().GetService(controllerType) ?? Activator.CreateInstance(controllerType));
        }
        catch (Exception ex)
        {
             throw new InvalidOperationException(String.Format(
                            CultureInfo.CurrentCulture,
                            MvcResources.DefaultControllerFactory_ErrorCreatingController,
                            controllerType),ex);
         }
       }
     }