public static void RegisterRoutes(RouteCollection routes)
{
 //MVC
 routes.MapRoute(
 name: "Default",
 url: "{controller}/{action}/{id}",
 defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
 );
 
 //WebForm
 routes.MapPageRoute(
 routeName: "WebForm",
 routeUrl: "Admin/{user}",
 physicalFile: "~/Admin/User.aspx"
 );
}

public class UrlRoutingModule : IHttpModule {
 public RouteCollection RouteCollection {
 get {
 if (_routeCollection == null) {
 //全局的RouteCollection集合
 _routeCollection = RouteTable.Routes;
 }
 return _routeCollection;
 }
 set {
 _routeCollection = value;
 }
 }
 
 protected virtual void Init(HttpApplication application) {
 //注冊(cè)PostResolveRequestCache事件
 application.PostResolveRequestCache += OnApplicationPostResolveRequestCache;
 }
 
 private void OnApplicationPostResolveRequestCache(object sender, EventArgs e) {
 //創(chuàng)建上下文
 HttpApplication app = (HttpApplication)sender;
 HttpContextBase context = new HttpContextWrapper(app.Context);
 PostResolveRequestCache(context);
 }
 
 public virtual void PostResolveRequestCache(HttpContextBase context) {
 //1.獲取RouteData
 RouteData routeData = RouteCollection.GetRouteData(context);
 if (routeData == null) {
 return;
 }
 //2.獲取IRouteHandler
 IRouteHandler routeHandler = routeData.RouteHandler;
 if (routeHandler == null) {
 
 }
 
 //RequestContext保證了HttpContext和RouteData,在后續(xù)使用
 RequestContext requestContext = new RequestContext(context, routeData);
 
 context.Request.RequestContext = requestContext;
 
 //3.獲取IHttpHandler
 IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);
 
 //重新映射到處理程序
 context.RemapHandler(httpHandler);
 }
}　　

public RouteData GetRouteData(HttpContextBase httpContext) {
 using (GetReadLock()) {
 foreach (RouteBase route in this) {
 RouteData routeData = route.GetRouteData(httpContext);
 if (routeData != null) { 
 return routeData;
 }
 }
 }
 return null;
}

public override RouteData GetRouteData(HttpContextBase httpContext) {
 string requestPath = httpContext.Request.AppRelativeCurrentExecutionFilePath.Substring(2) + httpContext.Request.PathInfo;
 
 //結(jié)合默認(rèn)值，匹配url
 RouteValueDictionary values = _parsedRoute.Match(requestPath, Defaults);
 
 if (values == null) {
 return null;
 }
 
 //包裝成RouteData，這里為什么不放在if后面呢？
 RouteData routeData = new RouteData(this, RouteHandler);
 
 //匹配約束
 if (!ProcessConstraints(httpContext, values, RouteDirection.IncomingRequest)) {
 return null;
 }
 
 //RouteData的Values和DataTokens都來自于Route
 foreach (var value in values) {
 routeData.Values.Add(value.Key, value.Value);
 }
 if (DataTokens != null) {
 foreach (var prop in DataTokens) {
 routeData.DataTokens[prop.Key] = prop.Value;
 }
 }
 
 return routeData;
}

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

public static Route MapRoute(this RouteCollection routes, string name, string url, object defaults, object constraints, string[] namespaces)
{
 //創(chuàng)建一個(gè)Route對(duì)象，它的IRouteHandler為MvcRouteHandler
 Route route = new Route(url, new MvcRouteHandler())
 {
 Defaults = CreateRouteValueDictionary(defaults),
 Constraints = CreateRouteValueDictionary(constraints),
 DataTokens = new RouteValueDictionary()
 };
 
 if ((namespaces != null) && (namespaces.Length > 0))
 {
 route.DataTokens["Namespaces"] = namespaces;
 }
 
 //將Route注冊(cè)到RouteCollection中
 routes.Add(name, route);
 
 return route;
}

protected virtual IHttpHandler GetHttpHandler(RequestContext requestContext)
{
 //設(shè)置session狀態(tài)
 requestContext.HttpContext.SetSessionStateBehavior(GetSessionStateBehavior(requestContext));
 
 //返回一個(gè)實(shí)現(xiàn)了IHttpHandler的MvcHandler
 return new MvcHandler(requestContext);
}

public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
{
 protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state)
 {
 IController controller;
 IControllerFactory factory;
 
 //這個(gè)方法里會(huì)激活Controller對(duì)象
 ProcessRequestInit(httpContext, out controller, out factory);
 
 IAsyncController asyncController = controller as IAsyncController;
 if (asyncController != null)
 {
 // asynchronous controller
 BeginInvokeDelegate beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState)
 {
 try
 {
 //調(diào)用Controller的BeginExecute方法
 return asyncController.BeginExecute(RequestContext, asyncCallback, asyncState);
 }
 catch
 {
 factory.ReleaseController(asyncController);
 throw;
 }
 };
 
 EndInvokeDelegate endDelegate = delegate(IAsyncResult asyncResult)
 {
 try
 {
 asyncController.EndExecute(asyncResult);
 }
 finally
 {
 factory.ReleaseController(asyncController);
 }
 };
 
 SynchronizationContext syncContext = SynchronizationContextUtil.GetSynchronizationContext();
 AsyncCallback newCallback = AsyncUtil.WrapCallbackForSynchronizedExecution(callback, syncContext);
 return AsyncResultWrapper.Begin(newCallback, state, beginDelegate, endDelegate, _processRequestTag);
 }
 else
 {
 // synchronous controller
 Action action = delegate
 {
 try
 {
 controller.Execute(RequestContext);
 }
 finally
 {
 factory.ReleaseController(controller);
 }
 };
 
 return AsyncResultWrapper.BeginSynchronous(callback, state, action, _processRequestTag);
 }
 }
}