通过前面几篇博文的介绍，现在我们已经清楚了asp.net请求管道是怎么一回事了，这篇博文来聊聊MVC的路由。

　　其实MVC的请求管道和Asp.Net请求管道一样，只是MVC扩展了UrlRoutingModule的动作。我们知道MVC网站启动后第一个请求会执行Global.asax文件中的Application_Start方法，完成一些初始化工作，其中就会注册路由，先来看下面一张图，该图可以直观的展示了MVC执行的流程。

 　　结合上图，我们一起来看看代码是如何实现路由的注册的。

protected void Application_Start() {      AreaRegistration.RegisterAllAreas();      RouteConfig.RegisterRoutes(RouteTable.Routes); } public class RouteConfig {     public static void RegisterRoutes(RouteCollection routes)     {        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");        routes.MapRoute(            name: "Default",            url: "{controller}/{action}/{id}",            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }        );     } }

RouteCollection通过MapRoute扩展方法拿着Url来创建Route并注册到RouteCollection其中，这一点我们通过源码可以看到该方法是如何操作的，该方法通过new一个MvcRouteHandler来创建Route。MvcRouteHandler创建了MvcHandler。紧接着继续往下执行，创建HttpApplication实例，执行后续事件，在PostResolveRequestCache事件去注册UrlRouteModule的动作。

// System.Web.Mvc.RouteCollectionExtensions/// 
Maps the specified URL route and sets default route values, constraints, and namespaces.
/// 
     
      A reference to the mapped route.
     /// A collection of routes for the application./// The name of the route to map./// The URL pattern for the route./// An object that contains default route values./// A set of expressions that specify values for the 
      parameter./// A set of namespaces for the application./// 
     
      The 
       or 
       parameter is null.
     public static Route MapRoute(this RouteCollection routes, string name, string url, object defaults, object constraints, string[] namespaces){    if (routes == null)    {        throw new ArgumentNullException("routes");    }    if (url == null)    {        throw new ArgumentNullException("url");    }    Route route = new Route(url, new MvcRouteHandler())    {        Defaults = RouteCollectionExtensions.CreateRouteValueDictionaryUncached(defaults),         Constraints = RouteCollectionExtensions.CreateRouteValueDictionaryUncached(constraints),         DataTokens = new RouteValueDictionary()    };    ConstraintValidation.Validate(route);    if (namespaces != null && namespaces.Length > 0)    {        route.DataTokens["Namespaces"] = namespaces;    }    routes.Add(name, route);    return route;}

using System;using System.Web.Mvc.Properties;using System.Web.Routing;using System.Web.SessionState;namespace System.Web.Mvc{    /// 
Creates an object that implements the IHttpHandler interface and passes the request context to it.
    public class MvcRouteHandler : IRouteHandler    {        private IControllerFactory _controllerFactory;        /// 
Initializes a new instance of the 
       class.
        public MvcRouteHandler()        {        }        /// 
Initializes a new instance of the 
       class using the specified factory controller object.
        /// The controller factory.        public MvcRouteHandler(IControllerFactory controllerFactory)        {            this._controllerFactory = controllerFactory;        }        /// 
Returns the HTTP handler by using the specified HTTP context.
        /// 
     
      The HTTP handler.
             /// The request context.        protected virtual IHttpHandler GetHttpHandler(RequestContext requestContext)        {            requestContext.HttpContext.SetSessionStateBehavior(this.GetSessionStateBehavior(requestContext));            return new MvcHandler(requestContext);        }        /// 
Returns the session behavior.
        /// 
     
      The session behavior.
             /// The request context.        protected virtual SessionStateBehavior GetSessionStateBehavior(RequestContext requestContext)        {            string text = (string)requestContext.RouteData.Values["controller"];            if (string.IsNullOrWhiteSpace(text))            {                throw new InvalidOperationException(MvcResources.MvcRouteHandler_RouteValuesHasNoController);            }            IControllerFactory controllerFactory = this._controllerFactory ?? ControllerBuilder.Current.GetControllerFactory();            return controllerFactory.GetControllerSessionBehavior(requestContext, text);        }        IHttpHandler IRouteHandler.GetHttpHandler(RequestContext requestContext)        {            return this.GetHttpHandler(requestContext);        }    }}

using System;using System.Globalization;using System.Runtime.CompilerServices;using System.Web.Security;namespace System.Web.Routing{    /// 
Matches a URL request to a defined route.
    [TypeForwardedFrom("System.Web.Routing, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=31bf3856ad364e35")]    public class UrlRoutingModule : IHttpModule    {        private static readonly object _contextKey = new object();        private static readonly object _requestDataKey = new object();        private RouteCollection _routeCollection;        /// 
Gets or sets the collection of defined routes for the ASP.NET application.
        /// 
     
      An object that contains the routes.
             public RouteCollection RouteCollection        {            get            {                if (this._routeCollection == null)                {                    this._routeCollection = RouteTable.Routes;                }                return this._routeCollection;            }            set            {                this._routeCollection = value;            }        }        /// 
Disposes of the resources (other than memory) that are used by the module.
        protected virtual void Dispose()        {        }        /// 
Initializes a module and prepares it to handle requests.
        /// An object that provides access to the methods, properties, and events common to all application objects in an ASP.NET application.        protected virtual void Init(HttpApplication application)        {            if (application.Context.Items[UrlRoutingModule._contextKey] != null)            {                return;            }            application.Context.Items[UrlRoutingModule._contextKey] = UrlRoutingModule._contextKey;            application.PostResolveRequestCache += new EventHandler(this.OnApplicationPostResolveRequestCache);        }        private void OnApplicationPostResolveRequestCache(object sender, EventArgs e)        {            HttpApplication httpApplication = (HttpApplication)sender;            HttpContextBase context = new HttpContextWrapper(httpApplication.Context);            this.PostResolveRequestCache(context);        }        /// 
Assigns the HTTP handler for the current request to the context.
        /// Encapsulates all HTTP-specific information about an individual HTTP request.        /// 
     
      The 
       property for the route is null.
             [Obsolete("This method is obsolete. Override the Init method to use the PostMapRequestHandler event.")]        public virtual void PostMapRequestHandler(HttpContextBase context)        {        }        /// 
Matches the HTTP request to a route, retrieves the handler for that route, and sets the handler as the HTTP handler for the current request.
        /// Encapsulates all HTTP-specific information about an individual HTTP request.        public virtual void PostResolveRequestCache(HttpContextBase context)        {            RouteData routeData = this.RouteCollection.GetRouteData(context);            if (routeData == null)            {                return;            }            IRouteHandler routeHandler = routeData.RouteHandler;            if (routeHandler == null)            {                throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, SR.GetString("UrlRoutingModule_NoRouteHandler"), new object[0]));            }            if (routeHandler is StopRoutingHandler)            {                return;            }            RequestContext requestContext = new RequestContext(context, routeData);            context.Request.RequestContext = requestContext;            IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);            if (httpHandler == null)            {                throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, SR.GetString("UrlRoutingModule_NoHttpHandler"), new object[]                {                    routeHandler.GetType()                }));            }            if (!(httpHandler is UrlAuthFailureHandler))            {                context.RemapHandler(httpHandler);                return;            }            if (FormsAuthenticationModule.FormsAuthRequired)            {                UrlAuthorizationModule.ReportUrlAuthorizationFailure(HttpContext.Current, this);                return;            }            throw new HttpException(401, SR.GetString("Assess_Denied_Description3"));        }        void IHttpModule.Dispose()        {            this.Dispose();        }        void IHttpModule.Init(HttpApplication application)        {            this.Init(application);        }    }}

　　到此，路由的注册动作也就告一段落。那么在理解了MVC的路由后，可以做什么呢？我们可以对路由做一些我们自己的扩展。

　　可以从三个层面来扩展路由：

　　一、在MapRoute范围内进行扩展，这种扩展只是在扩展正则表达式

public static void RegisterRoutes(RouteCollection routes)        {            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");//忽略路由                                                             //mvc路由规则下的扩展            routes.IgnoreRoute("Handler/{*pathInfo}");            routes.MapRoute(             name: "About",             url: "about",//不区分大小写             defaults: new { controller = "First", action = "String", id = UrlParameter.Optional }            );//静态路由            routes.MapRoute("TestStatic", "Test/{action}", new { controller = "Second" });//替换控制器            routes.MapRoute(                    "Regex",                     "{controller}/{action}_{Year}_{Month}_{Day}",                     new { controller = "First", id = UrlParameter.Optional },                     new { Year = @"^\d{4}", Month = @"\d{2}", Day = @"\d{2}" }                       );//正则路由            routes.MapRoute(                name: "Default",                url: "{controller}/{action}/{id}",                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional },                namespaces: new string[] { "Jesen.Web.Controllers" }            );                  }

 

　　二、通过继承RouteBase来扩展Route，这种扩展可以随意的定制规则，而不仅仅是表达式

/// 
    /// 直接扩展route    /// 
    public class MyRoute : RouteBase    {        /// 
        /// 解析路由信息        /// 
        ///         /// 
             public override RouteData GetRouteData(HttpContextBase httpContext)        {
    　　　　　　　//此处可以根据自己的需求做一些路由的配置，例如拒绝某个浏览器的访问，检测到Chrome浏览器，则直接跳转到某个url            if (httpContext.Request.UserAgent.IndexOf("Chrome/69.0.3497.92") >= 0)            {                RouteData rd = new RouteData(this, new MvcRouteHandler());                rd.Values.Add("controller", "Pipe");                rd.Values.Add("action", "Refuse");                return rd;            }            return null;        }        /// 
        /// 指定处理的虚拟路径        /// 
        ///         ///         /// 
             public override VirtualPathData GetVirtualPath(RequestContext requestContext, RouteValueDictionary values)        {            return null;        }    }

接着在RouteConfig和Global.asax中注册该路由

public static void RegisterMyRoutes(RouteCollection routes){    routes.Add(new MyRoute());}protected void Application_Start(){    RouteConfig.RegisterMyRoutes(RouteTable.Routes);}

　　

　　三、扩展Handler，不一定是MvcHandler，可以是我们熟悉的IHttpHandler

 

/// 
    /// 扩展IRouteHandler /// 
    public class MyRouteHandler : IRouteHandler    {        public IHttpHandler GetHttpHandler(RequestContext requestContext)        {            return new MyHttpHandler(requestContext);        }    }    /// 
    /// 扩展IHttpHandler    /// 
    public class MyHttpHandler : IHttpHandler    {        public MyHttpHandler(RequestContext requestContext)        {                    }        public void ProcessRequest(HttpContext context)        {            string url = context.Request.Url.AbsoluteUri;            context.Response.Write((string.Format("当前地址为：{0}", url)));            context.Response.End();        }        public virtual bool IsReusable        {            get            {                return false;            }        }    }

RouteConfig.cs文件中配置路由

public static void RegisterMyMVCHandler(RouteCollection routes)  {      routes.Add(new Route("MyMVC/{*Info}", new MyRouteHandler()));  }

Global中注册路由

RouteConfig.RegisterMyMVCHandler(RouteTable.Routes);

运行看结果