asp.net mvc路由篇 如何找到 IHttpHandler方法介绍

protected virtual void Init(HttpApplication application) 
{ 
if (application.Context.Items[_contextKey] == null) 
{ 
application.Context.Items[_contextKey] = _contextKey; 
application.PostResolveRequestCache += new EventHandler(this.OnApplicationPostResolveRequestCache); 
} 
} 
private void OnApplicationPostResolveRequestCache(object sender, EventArgs e) 
{ 
HttpContextBase context = new HttpContextWrapper(((HttpApplication) sender).Context); 
this.PostResolveRequestCache(context); 
} 
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.CurrentUICulture, SR.GetString("UrlRoutingModule_NoRouteHandler"), new object[0])); 
} 
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); 
} 
} 
} 
} 
 
在IHttpModule.Init中注册了一个PostResolveRequestCache事件，而该事件主要是调用PostResolveRequestCache这个方法，在这个方法里面有几句很重要的代码是 
 代码如下:

RouteData routeData = this.RouteCollection.GetRouteData(context); 
IRouteHandler routeHandler = routeData.RouteHandler; 
RequestContext requestContext = new RequestContext(context, routeData); 
context.Request.RequestContext = requestContext; 
IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext); 
context.RemapHandler(httpHandler); 
 
让我们来分析第一句RouteData routeData = this.RouteCollection.GetRouteData(context) ，这句我们猜测是获取路由信息。要想理解这句代码又得回到我们程序中来，我们在Global.asax.cs文件中的RegisterRoutes方法中，默认有这么一句 
 代码如下:

routes.MapRoute( 
"Default", // 路由名称 
"{controller}/{action}/{id}", // 带有参数的 URL 
new { controller = "Home", action = "Index", id = UrlParameter.Optional } // 参数默认值 
); 
 
这句代码主要是注册一个路由，这里的url要注意不能随便写，需要有controller和action。具体是怎么实现的了？ 
 代码如下:

public static Route MapRoute(this RouteCollection routes, string name, string url, object defaults, object constraints, string[] namespaces) { 
Route route = new Route(url, new MvcRouteHandler()) { 
Defaults = new RouteValueDictionary(defaults), 
Constraints = new RouteValueDictionary(constraints), 
DataTokens = new RouteValueDictionary() 
}; 
if ((namespaces != null) && (namespaces.Length > 0)) { 
route.DataTokens["Namespaces"] = namespaces; 
} 
routes.Add(name, route); 
return route; 
} 
 
各参数如下 
 代码如下:

routeName="Default", // 路由名称 
routeUrl= "{controller}/{action}/{id}", // 带有参数的 URL 
defaults=new { controller = "Home", action = "Index", id = UrlParameter.Optional } // 参数默认值 
constraints=null 
namespaces=null 
 
在这里创建了一个Route实例并且把它加入到RouteCollection中了。 
现在又让我们回到 RouteData routeData = this.RouteCollection.GetRouteData(context);这句代码中来，GetRouteData的主要代码如下： 
 代码如下:

public RouteData GetRouteData(HttpContextBase httpContext) 
{ 
using (this.GetReadLock()) 
{ 
foreach (RouteBase base2 in this) 
{ 
RouteData routeData = base2.GetRouteData(httpContext); 
if (routeData != null) 
{ 
return routeData; 
} 
} 
} 
return null; 
} 
 
在这里的base2就是我们先前调用MapRoute是添加的Route的。而Route的GetRouteData的方法如下： 
 代码如下:

public override RouteData GetRouteData(HttpContextBase httpContext) 
{ 
string virtualPath = httpContext.Request.AppRelativeCurrentExecutionFilePath.Substring(2) + httpContext.Request.PathInfo; 
RouteValueDictionary values = this._parsedRoute.Match(virtualPath, this.Defaults); 
if (values == null) 
{ 
return null; 
} 
RouteData data = new RouteData(this, this.RouteHandler); 
if (!this.ProcessConstraints(httpContext, values, RouteDirection.IncomingRequest)) 
{ 
return null; 
} 
foreach (KeyValuePair<string, object> pair in values) 
{ 
data.Values.Add(pair.Key, pair.Value); 
} 
if (this.DataTokens != null) 
{ 
foreach (KeyValuePair<string, object> pair2 in this.DataTokens) 
{ 
data.DataTokens[pair2.Key] = pair2.Value; 
} 
} 
return data; 
} 
 
这个方法很复杂，有许多验证和检查，我们主要关心一句 RouteData data = new RouteData(this, this.RouteHandler); 
当然剩下 RequestContext requestContext = new RequestContext(context, routeData); 
context.Request.RequestContext = requestContext;这2句没什么特别了。 
现在让我们来看看IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);这句究竟干了些什么，意思很明白获取Httphandler。 
那么MvcRouteHandler是如何获取一个Httphandler的了， 
 代码如下:

protected virtual IHttpHandler GetHttpHandler(RequestContext requestContext) { 
requestContext.HttpContext.SetSessionStateBehavior(GetSessionStateBehavior(requestContext)); 
return new MvcHandler(requestContext); 
} 
 
直接返回了一个MvcHandler实例。 
最有一句context.RemapHandler(httpHandler); 很简单很好明白吧，在HttpContext的RemapHandler方法中有这么一句 this._remapHandler = handler; 
在HttpContext中有这个属性 
 代码如下:

internal IHttpHandler RemapHandlerInstance 
{ 
get 
{ 
return this._remapHandler; 
} 
} 
 
那么这个东西又是什么时候调用的了，在HttpApplication的内部类MaterializeHandlerExecutionStep中的 void HttpApplication.IExecutionStep.Execute()方法调用 
 代码如下:

if (httpContext.RemapHandlerInstance != null) 
{ 
httpContext.Handler = httpContext.RemapHandlerInstance; 
} 
 
看到MaterializeHandlerExecutionStep这个了类名，我想大家都能猜到吧。在内部类PipelineStepManager中BuildSteps方法有 
 代码如下:

HttpApplication.IExecutionStep step = new HttpApplication.MaterializeHandlerExecutionStep(app); 
app.AddEventMapping("ManagedPipelineHandler", RequestNotification.MapRequestHandler, false, step); 
 
我想大家看到这里对mvc整个路由应该有个大致的理解了吧。