003. Asp.Net Routing与MVC 之一： 请求如何到达MVC

   1: <?xml version="1.0" encoding="utf-8"?>

   2: <!-- the root web configuration file -->

   3: <configuration>

   4:     <system.web>

   5:         <httpModules>

   6:             <add name="UrlRoutingModule-4.0" type="System.Web.Routing.UrlRoutingModule" />

   7:         </httpModules>

   8:     </system.web>

   9: </configuration>

   1: //UrlRoutingModule 位于 System.web.dll 文件中，利用Reflector 可以查看到其源码

   2: [TypeForwardedFrom("System.Web.Routing, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=31bf3856ad364e35")]

   3: public class UrlRoutingModule : IHttpModule

   4: {

   5:     // Fields

   6:     private static readonly object _contextKey = new object();

   7:     private static readonly object _requestDataKey = new object();

   8:     private RouteCollection _routeCollection;

   9:     // Methods

  10:     protected virtual void Dispose()  {}

  11:  

  12:     //在II7处理管道中注册了的IHttpModule类型，其_Init()会被执行，以在II7处理管道中注册事件处理方法。

  13:     protected virtual void Init(HttpApplication application)

  14:     {

  15:         if (application.Context.Items[_contextKey] == null)

  16:         {

  17:             application.Context.Items[_contextKey] = _contextKey;

  18:             //这里为UrlRoutingModule 注册了一个PostResolveRequestCache 事件处理方法：OnApplicationPostResolveRequestCache().

  19:             application.PostResolveRequestCache += new EventHandler(this.OnApplicationPostResolveRequestCache);

  20:         }

  21:     }

  22:  

  23:     //发生PostResolveRequestCache 事件时，该方法被调用

  24:     private void OnApplicationPostResolveRequestCache(object sender, EventArgs e)

  25:     {

  26:         HttpContextBase context = new HttpContextWrapper(((HttpApplication) sender).Context);

  27:         //执行真正的处理 PostResolveRequestCache()

  28:         this.PostResolveRequestCache(context);

  29:     }

  30:  

  31:     [Obsolete("This method is obsolete. Override the Init method to use the PostMapRequestHandler event.")]

  32:     public virtual void PostMapRequestHandler(HttpContextBase context)

  33:     {

  34:     }

  35:  

  36:      //发生PostResolveRequestCache 事件时真正的处理

  37:     public virtual void PostResolveRequestCache(HttpContextBase context)

  38:     {

  39:         //获取路由信息（RouteCollection是其本身的属性，见this.RouteCollection）

  40:         RouteData routeData = this.RouteCollection.GetRouteData(context);

  41:         if (routeData != null)

  42:         {

  43:             //从routeData 获取 RouteHandler

  44:             // 既然routeData 内容其实来自System.Web.Routing.RouteTable.Routes

  45:             // 那么System.Web.Routing.RouteTable.Routes 里的RouteHandler到底是哪来的呢？我们需要去MVC项目里看看

  46:             IRouteHandler routeHandler = routeData.RouteHandler;

  47:             if (routeHandler == null)

  48:             {

  49:                 throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, 

  50:                                 SR.GetString("UrlRoutingModule_NoRouteHandler"), new object[0]));

  51:             }

  52:             if (!(routeHandler is StopRoutingHandler))

  53:             {

  54:                 //构建请求上下文

  55:                 RequestContext requestContext = new RequestContext(context, routeData);

  56:                 context.Request.RequestContext = requestContext;

  57:                 //调用routeHandler.GetHttpHandler()，获取的IHttpHandler 类型实例 

  58:                 IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);

  59:                 if (httpHandler == null)

  60:                 {

  61:                     throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, 

  62:                                     SR.GetString("UrlRoutingModule_NoHttpHandler"), new object[] { routeHandler.GetType() }));

  63:                 }

  64:                 if (httpHandler is UrlAuthFailureHandler)

  65:                 {

  66:                     if (!FormsAuthenticationModule.FormsAuthRequired)

  67:                     {

  68:                         throw new HttpException(0x191, SR.GetString("Assess_Denied_Description3"));

  69:                     }

  70:                     UrlAuthorizationModule.ReportUrlAuthorizationFailure(HttpContext.Current, this);

  71:                 }

  72:                 else

  73:                 {

  74:                     //合适条件下，把之前将获取的IHttpHandler 类型实例 映射到IIS HTTP处理管道中

  75:                     context.RemapHandler(httpHandler);

  76:                 }

  77:             }

  78:         }

  79:     }

  80:  

  81:     void IHttpModule.Dispose()

  82:     {

  83:         this.Dispose();

  84:     }

  85:  

  86:     void IHttpModule.Init(HttpApplication application)

  87:     {

  88:         this.Init(application);

  89:     }

  90:  

  91:     // Properties

  92:     public RouteCollection RouteCollection

  93:     {

  94:         get

  95:         {

  96:             //恩，原来真实内容来自System.Web.Routing.RouteTable.Routes

  97:             if (this._routeCollection == null)

  98:             {

  99:                 this._routeCollection = RouteTable.Routes;

 100:             }

 101:             return this._routeCollection;

 102:         }

 103:         set

 104:         {

 105:             this._routeCollection = value;

 106:         }

 107:     }

 108: }

   1: //PostResolveRequestCache方法里的核心代码：

   2:  

   3: //获取路由信息（RouteCollection是其本身的属性，见this.RouteCollection）

   4: RouteData routeData = this.RouteCollection.GetRouteData(context);

   5: //从routeData 获取 RouteHandler

   6: // 既然routeData 内容其实来自System.Web.Routing.RouteTable.Routes

   7: // 那么System.Web.Routing.RouteTable.Routes 里的RouteHandler到底是哪来的呢？我们需要去MVC项目里看看

   8: IRouteHandler routeHandler = routeData.RouteHandler;

   9:  

  10: //调用routeHandler.GetHttpHandler()，获取的IHttpHandler 类型实例 

  11: IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);

  12:  

  13: //合适条件下，把之前将获取的IHttpHandler 类型实例 映射到IIS HTTP处理管道中

  14: context.RemapHandler(httpHandler);

   1: //这是一个普通MVC5 WebApp的Global.asax.cs

   2: namespace WebApplication1

   3: {

   4:     public class MvcApplication : System.Web.HttpApplication

   5:     {

   6:         protected void Application_Start()

   7:         {

   8:             AreaRegistration.RegisterAllAreas();

   9:             FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);

  10:             //这里要注册路由了

  11:             RouteConfig.RegisterRoutes(RouteTable.Routes);

  12:             BundleConfig.RegisterBundles(BundleTable.Bundles);

  13:         }

  14:     }

  15:  

  16:     //为方便起见，我把项目App_Start/RouteConfig.cs内容放在一起

  17:     public class RouteConfig

  18:     {

  19:         public static void RegisterRoutes(RouteCollection routes)

  20:         {

  21:             routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

  22:             //玄机就在这了，这个MapRoute位于System.Web.Mvc.RouteCollectionExtensions

  23:             //看RouteCollectionExtensions里面做了什么

  24:             routes.MapRoute(

  25:                 name: "Default",

  26:                 url: "{controller}/{action}/{id}",

  27:                 defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }

  28:             );

  29:         }

  30:     }

  31: }

   1: //System.Web.Mvc.RouteCollectionExtensions.MapRoute 众多重载的最终执行者代码

   2: [SuppressMessage("Microsoft.Design", "CA1054:UriParametersShouldNotBeStrings", MessageId = "2#", Justification = "This is not a regular URL as it may contain special routing characters.")]

   3: public static Route MapRoute(this RouteCollection routes, string name, string url, object defaults, object constraints, string[] namespaces)

   4: {

   5:     if (routes == null)

   6:     {

   7:         throw new ArgumentNullException("routes");

   8:     }

   9:     if (url == null)

  10:     {

  11:         throw new ArgumentNullException("url");

  12:     }

  13:  

  14:     //终于找到了，“new MvcRouteHandler()”，

  15:     //直接把一个 MvcRouteHandler 实例塞到 System.Web.Routing 的初始化方法里了！

  16:     Route route = new Route(url, new MvcRouteHandler())

  17:     {

  18:         Defaults = CreateRouteValueDictionaryUncached(defaults),

  19:         Constraints = CreateRouteValueDictionaryUncached(constraints),

  20:         DataTokens = new RouteValueDictionary()

  21:     };

  22:  

  23:     ConstraintValidation.Validate(route);

  24:  

  25:     if ((namespaces != null) && (namespaces.Length > 0))

  26:     {

  27:         route.DataTokens[RouteDataTokenKeys.Namespaces] = namespaces;

  28:     }

  29:  

  30:     routes.Add(name, route);

  31:  

  32:     return route;

  33: }