asp.net mvc路由篇如何找到 IHttpHandler方法介紹

更新時(shí)間：2012年11月08日 13:56:31 作者：

學(xué)習(xí)是使用asp.net已經(jīng)有很長(zhǎng)一段時(shí)間了，現(xiàn)在就來分析一下mvc的整過過程吧。個(gè)人計(jì)劃寫一個(gè)mvc系列的博文，僅從源代碼的角度來分析mvc。在接觸mvc時(shí)我們一定會(huì)經(jīng)歷路由，那么路由這東東是怎么搞出來的啊。在我們的web.config中有這么一句： <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /> 看來路由是它咋負(fù)責(zé)了。在這個(gè)dll中有一個(gè)很特殊的類UrlRoutingModule
我們來看看它里面主要的核心代碼吧：

復(fù)制代碼代碼如下:

 
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中注冊(cè)了一個(gè)PostResolveRequestCache事件，而該事件主要是調(diào)用PostResolveRequestCache這個(gè)方法，在這個(gè)方法里面有幾句很重要的代碼是

復(fù)制代碼代碼如下:

 
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); 

讓我們來分析第一句RouteData routeData = this.RouteCollection.GetRouteData(context) ，這句我們猜測(cè)是獲取路由信息。要想理解這句代碼又得回到我們程序中來，我們?cè)贕lobal.asax.cs文件中的RegisterRoutes方法中，默認(rèn)有這么一句

復(fù)制代碼代碼如下:

 
routes.MapRoute( 
"Default", // 路由名稱 
"{controller}/{action}/{id}", // 帶有參數(shù)的 URL 
new { controller = "Home", action = "Index", id = UrlParameter.Optional } // 參數(shù)默認(rèn)值 
); 

這句代碼主要是注冊(cè)一個(gè)路由，這里的url要注意不能隨便寫，需要有controller和action。具體是怎么實(shí)現(xiàn)的了？

復(fù)制代碼代碼如下:

 
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; 
} 

各參數(shù)如下

復(fù)制代碼代碼如下:

 
routeName="Default", // 路由名稱 
routeUrl= "{controller}/{action}/{id}", // 帶有參數(shù)的 URL 
defaults=new { controller = "Home", action = "Index", id = UrlParameter.Optional } // 參數(shù)默認(rèn)值 
constraints=null 
namespaces=null 

在這里創(chuàng)建了一個(gè)Route實(shí)例并且把它加入到RouteCollection中了。
現(xiàn)在又讓我們回到 RouteData routeData = this.RouteCollection.GetRouteData(context);這句代碼中來，GetRouteData的主要代碼如下：

復(fù)制代碼代碼如下:

 
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; 
} 

在這里的base2就是我們先前調(diào)用MapRoute是添加的Route的。而Route的GetRouteData的方法如下：

復(fù)制代碼代碼如下:

 
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; 
} 

這個(gè)方法很復(fù)雜，有許多驗(yàn)證和檢查，我們主要關(guān)心一句 RouteData data = new RouteData(this, this.RouteHandler);
當(dāng)然剩下 RequestContext requestContext = new RequestContext(context, routeData);
context.Request.RequestContext = requestContext;這2句沒什么特別了。
現(xiàn)在讓我們來看看IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);這句究竟干了些什么，意思很明白獲取Httphandler。
那么MvcRouteHandler是如何獲取一個(gè)Httphandler的了，

復(fù)制代碼代碼如下:

 
protected virtual IHttpHandler GetHttpHandler(RequestContext requestContext) { 
requestContext.HttpContext.SetSessionStateBehavior(GetSessionStateBehavior(requestContext)); 
return new MvcHandler(requestContext); 
} 

直接返回了一個(gè)MvcHandler實(shí)例。
最有一句context.RemapHandler(httpHandler); 很簡(jiǎn)單很好明白吧，在HttpContext的RemapHandler方法中有這么一句 this._remapHandler = handler;
在HttpContext中有這個(gè)屬性

復(fù)制代碼代碼如下:

 
internal IHttpHandler RemapHandlerInstance 
{ 
get 
{ 
return this._remapHandler; 
} 
} 

那么這個(gè)東西又是什么時(shí)候調(diào)用的了，在HttpApplication的內(nèi)部類MaterializeHandlerExecutionStep中的 void HttpApplication.IExecutionStep.Execute()方法調(diào)用

復(fù)制代碼代碼如下:

 
if (httpContext.RemapHandlerInstance != null) 
{ 
httpContext.Handler = httpContext.RemapHandlerInstance; 
} 

看到MaterializeHandlerExecutionStep這個(gè)了類名，我想大家都能猜到吧。在內(nèi)部類PipelineStepManager中BuildSteps方法有

復(fù)制代碼代碼如下:

 
HttpApplication.IExecutionStep step = new HttpApplication.MaterializeHandlerExecutionStep(app); 
app.AddEventMapping("ManagedPipelineHandler", RequestNotification.MapRequestHandler, false, step); 

我想大家看到這里對(duì)mvc整個(gè)路由應(yīng)該有個(gè)大致的理解了吧。

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