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31: [Obsolete("This method is obsolete.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: }
终于找到了！
综上所述，一个请求从 IIS 到达 MvcRouteHandler 的顺序如下：
一、IIS接到请求：
IIS接到一个请求，检查请求的应用是否已初始化；
若应用未初始化，为应用分配应用池程序资源，及其他应用程序域信息，加载全局和本站web.config信息以设定配置；
开始应用初始化；
二、开始应用初始化：
1.1、在应用程序域，为应用程序创建环境对象（HostingEnvironment??）和响应对象（HttpContext、HttpRequest 和 HttpResponse）；
创建应用的 HttpApplication 类型实例（即Global.asax.cs 实例），以启动应用；
1.2、在Global.asax.cs中，调用程序 RegisterRoutes 注册路由。
1.3、在 RegisterRoutes 中，调用 System.Web.Mvc.RouteCollectionExtensions.MapRoute()逐条注册。
1.4、在MapRoute中，直接把 MvcRouteHandler 类型实例塞到 System.Web.Routing 的初始化方法里，以填充System.Web.Routing.RouteTable.Routes数据。
三、初始化完成，处理请求：
1、HttpApplication 启动HTTP管道模型开始处理请求
HTTP管道处理已注册的 IHttpModule 事件：System.Web.Routing.UrlRoutingModule.OnApplicationPostResolveRequestCache();
随即OnApplicationPostResolveRequestCache 调用 PostResolveRequestCache()
PostResolveRequestCache方法从System.Web.Routing.RouteTable.Routes的数据中获取IHttpHandler 类型；
在2.4中被直接塞入的MvcRouteHandler 类型实例，被映射到 IIS HTTP处理管道中。
最终，IIS HTTP处理管道调用 MvcRouteHandler 处理请求，并返回Response内容。
至此，请求 成功透过 Asp.Net Routing机制到达 MVC 处理程序。
下次讲 Asp.Net Routing在MVC项目中的使用
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http://www.cnblogs.com/fsjohnhuang/articles/2332074.html
http://msdn.microsoft.com/zh-cn/library/cc668201%28v=vs.100%29.aspx
http://www.cnblogs.com/isdavid/archive/2013/05/28/3103228.html
http://www.iis.net/learn/get-started/introduction-to-iis/introduction-to-iis-architecture
http://blog.csdn.net/darren__chan/article/details/8215646
http://msdn.microsoft.com/zh-cn/library/bb470252%28v=vs.100%29.aspx
http://www.bdqn.cn/news/201309/11384.shtml
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003. Asp.Net Routing与MVC 之一： 请求如何到达MVC