简单的mvc之三：灵活的路由(上)

　　在上一篇关于管线的随笔中已经提及了管线，通过对管线的分析，我们可以得到下面几个结论：路由系统由URLRoutingModule模块实现，它订阅了PostResolvRequestCache事件；路由系统通过查阅路由并尽可能的通过RemapHandler方法，确定excuteHandler阶段执行的IHttphandler。这一篇随笔想详细谢谢路由的定义、注册和导航的具体过程。

　　路由系统的导航过程定义于URLRoutingModule，具体实现如下：

 public virtual void PostResolveRequestCache(HttpContextBase context)
 {
     RouteData routeData = this.RouteCollection.GetRouteData(context);
     if (routeData != null)
     {
         IRouteHandler routeHandler = routeData.RouteHandler;
         if (routeHandler == null)
         {
             throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, SR.GetString("UrlRoutingModule_NoRouteHandler"), new object[]));
         }
         if (!(routeHandler is StopRoutingHandler))
         {
             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)
             {
                 if (!FormsAuthenticationModule.FormsAuthRequired)
                 {
                     throw new HttpException(0x191, SR.GetString("Assess_Denied_Description3"));
                 }
                 UrlAuthorizationModule.ReportUrlAuthorizationFailure(HttpContext.Current, this);
             }
             else
             {
                 context.RemapHandler(httpHandler);
             }
         }
     }
 }

代码中可以很明显看出导航逻辑：通过全局全局路由表Routeable.Routes.GetRouteData()方法获得RouteData，然后通过RouteData.GetHttphandler()获得IRoutehandler,最后通过HttpContext.RemapHandler()注册IRouteHandler.GetHttpHandler()得到的IhttpHandler。代码中的出现的StopRoutingHandler后面再说。

　　路由表的切入口在全局静态类RouteTable.Routes，注册的过程放在HttpApplication的Appliation_Start方法中，这个方法如同静态构造函数一般，只启动一次，所以所有需要初始化的全局对象都可以放在这个方法中。vs建立的项目中，Route表的注册被分离出来，放在了App_Start文件夹中，使代码更加清晰。例如以下代码所示，3个路由被注册：

 public static void RegisterRoutes(RouteCollection routes) {
     routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

     routes.MapRoute(
         name: "Default",
         url: "{controller}/{action}/{id}",
         defaults: new { controller = "Self", action = "Index", id = UrlParameter.Optional }
     );

     routes.MapRoute(
         name: "CatchAll",
         url: "{*input}",
         defaults: new { controller = "Home", action = "index" }
     );
 }

上面的代码中使用的IgnoreRoute（）与MapRoute（）皆为扩展方法，用来简化路由注册过程，前者初始化一个Route对象，或者初始化一个IgnoreRouteInternal（继承于Route,私有封闭）对象，然后使用RouteTable.Routes.Add()方法添加如注册表。通过如下代码，可以清楚的看到注册的route:

 public void Routes() {
     foreach (var routeBase in RouteTable.Routes) {
         var route = routeBase as Route;
         if (route != null) {
             Response.Write(String.Format("{1,26}  {0}<br/>",
                 route.GetType().ToString(), route.Url
             ).Replace(" ","&nbsp;"));
         } else {
             Response.Write(String.Format("other:{0}<br/>", routeBase.GetType()));
         }
     }
 }

得到的结果如下：

从图中我们可以看到后3个路由正是我们已经注册的3个路由，至于第一个路由，实际上是托管于asp.net的web api应用路由，这个后面再说。同时图中的第二列的Type也佐证了上面所说的不同的Route类说法。

　　那么Route类的具体实现呢？首先我们看看Route的继承树：

　　

看着很熟悉，因为集成树中的类在上述的路由图中已经全部出现，整个树的基类是RouteBase,也就是图中高亮的那个，Routes中的集合类型也是RouteBase,下面是RouteBase的定义：

 [TypeForwardedFrom("System.Web.Routing, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=31bf3856ad364e35")]
 public abstract class RouteBase
 {
     // Fields
     private bool _routeExistingFiles;

     // Methods
     protected RouteBase();
     public abstract RouteData GetRouteData(HttpContextBase httpContext);
     public abstract VirtualPathData GetVirtualPath(RequestContext requestContext, RouteValueDictionary values);

     // Properties
     public bool RouteExistingFiles { [TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] get; [TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] set; }
 }

这个一个抽象类，核心方法就是URLRouting中出现过的GetRouteData()方法，还有一个很重要的属性—RouteExistingFiles，这个属性一般用来实现对.aspx兼容支持。RouteBase最常用也是最重要的子类便是Route,代码如下：

 [TypeForwardedFrom("System.Web.Routing, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=31bf3856ad364e35")]
 public class Route : RouteBase
 {
     // Fields
     private ParsedRoute _parsedRoute;
     private string _url;
     private const string HttpMethodParameterName = "httpMethod";

     // Methods
     public Route(string url, IRouteHandler routeHandler);
     public Route(string url, RouteValueDictionary defaults, IRouteHandler routeHandler);
     public Route(string url, RouteValueDictionary defaults, RouteValueDictionary constraints, IRouteHandler routeHandler);
     public Route(string url, RouteValueDictionary defaults, RouteValueDictionary constraints, RouteValueDictionary dataTokens, IRouteHandler routeHandler);
     public override RouteData GetRouteData(HttpContextBase httpContext);
     public override VirtualPathData GetVirtualPath(RequestContext requestContext, RouteValueDictionary values);
     protected virtual bool ProcessConstraint(HttpContextBase httpContext, object constraint, string parameterName, RouteValueDictionary values, RouteDirection routeDirection);
     private bool ProcessConstraints(HttpContextBase httpContext, RouteValueDictionary values, RouteDirection routeDirection);

     // Properties
     public RouteValueDictionary Constraints { get; [CompilerGenerated, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] set; }
     public RouteValueDictionary DataTokens { [CompilerGenerated, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] get; [CompilerGenerated, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] set; }
     public RouteValueDictionary Defaults { [CompilerGenerated, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] get; [CompilerGenerated, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] set; }
     public IRouteHandler RouteHandler { [CompilerGenerated, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] get; [CompilerGenerated, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] set; }
     public string Url { get; set; }
 }

相较于RouteBase,Route有5个属性，其中Url,Constraints用来过滤进入请求进行匹配，RouteHandler用来返回IHttpHandler,DataTokens与Defaults则应用于后面的控制器查找，激活与数据传递。这些就以后在细节补充中说这里就不散开了。

　　从上面的Route的定义结合最前面说的导航过程，RouteBase->IRouteHandler->IhttpHandler的过程清晰可见。在前面曾经搁置的类StopRoutingHandler就属于IRoutehandler，而这个RouteHandler并不是由Route类获得的，而是前面出现的IgnoreRoute获得的，相关代码：

 public IgnoreRouteInternal(string url) : base(url, new StopRoutingHandler())
 {
 }

到这里IgnoreRoute()的方法的作用就真正明了了，和MapRoute()方法想反，它定义的不是对某一类路径的拦截，而是放弃对某一类路径的拦截，以便留给后面的管线过程处理，这个管线过程就是后面要说的ExcuteHandler过程（内部，没有公开事件），具体到文中注册的路由可以看到它放弃的是对*.axd类地址的拦截。但是注册的好处是直接跳过，提高效率。

　　本来想一次说完的，写到这里发现还有很多没写到，比如全局类型RouteTable等，那就分上下篇吧。最后留个问题：两个路由，一个的Url定义为{input},一个定义为｛*input｝，二者有什么区别？