003. Asp.Net Routing与MVC 之一：请求如何到达MVC

时间：2014-07-26 14:01:40 阅读：454 评论：0 收藏：0 [点我收藏+]

前言

本文用到的基础知识：URL、HttpModule 与 HttpHandler、IIS7.0的请求处理过程。

URL
参见《基础URL》，

HttpModule与HttpHandler
请读《HttpModule 、HttpHandler》

IIS7.0的请求处理过程
请读《IIS7的》
《IIS架构》

OK，现在我们来看请求如何到达MVC：

一、请求如何到达Asp.Net Routing

我们知道IIS网站的配置可以分为两个块：全局 Web.Config 和本站 Web.Config 。

Asp.Net Routing属于全局性的，所以它配置在全局Web.Config 中，我们可以在如下路径中找到：

“$\Windows\Microsoft.NET\Framework\版本号\Config\Web.config“

   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>

通过在全局Web.Config中注册 System.Web.Routing.UrlRoutingModule，IIS请求处理管道接到请求后，就会加载 UrlRoutingModule类型的Init()方法。其源码入下：

   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 28:         this.PostResolveRequestCache(context);  29:     }  30:    31:     [Obsolete("This method is obsolete.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: }

下边是PostResolveRequestCache方法里的几句核心代码：

   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);

好吧，我们需要去MVC项目里看看。众所周知，项目启动是从Global开始的，那就看看它。下边是代码：

   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: }

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

   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: }