asp.net mvc路由篇 如何找到 IHttpHandler方法介紹

學習是使用asp.net已經有很長一段時間了，現在就來分析一下mvc的整過過程吧。個人排程寫一個mvc系列的博文，僅從原始碼的角度來分析mvc。在接觸mvc時我們一定會經曆路由，那麼路由這東東是怎麼搞出來的啊。在我們的web.config中有這麼一句： <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /> 看來路由是它咋負責了。在這個dll中有一個很特殊的類UrlRoutingModule
我們來看看它裡面主要的核心代碼吧： 複製代碼 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中註冊了一個PostResolveRequestCache事件，而該事件主要是調用PostResolveRequestCache這個方法，在這個方法裡面有幾句很重要的代碼是 複製代碼 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) ，這句我們猜測是擷取路由資訊。要想理解這句代碼又得回到我們程式中來，我們在Global.asax.cs檔案中的RegisterRoutes方法中，預設有這麼一句 複製代碼 代碼如下:routes.MapRoute(
"Default", // 路由名稱
"{controller}/{action}/{id}", // 帶有參數的 URL
new { controller = "Home", action = "Index", id = UrlParameter.Optional } // 參數預設值
);

這句代碼主要是註冊一個路由，這裡的url要注意不能隨便寫，需要有controller和action。具體是怎麼實現的了？ 複製代碼 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;
}

各參數如下 複製代碼 代碼如下:routeName="Default", // 路由名稱
routeUrl= "{controller}/{action}/{id}", // 帶有參數的 URL
defaults=new { controller = "Home", action = "Index", id = UrlParameter.Optional } // 參數預設值
constraints=null
namespaces=null

在這裡建立了一個Route執行個體並且把它加入到RouteCollection中了。
現在又讓我們回到 RouteData routeData = this.RouteCollection.GetRouteData(context);這句代碼中來，GetRouteData的主要代碼如下： 複製代碼 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;
}

在這裡的base2就是我們先前調用MapRoute是添加的Route的。而Route的GetRouteData的方法如下： 複製代碼 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;
}

這個方法很複雜，有許多驗證和檢查，我們主要關心一句 RouteData data = new RouteData(this, this.RouteHandler);
當然剩下 RequestContext requestContext = new RequestContext(context, routeData);
context.Request.RequestContext = requestContext;這2句沒什麼特別了。
現在讓我們來看看IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);這句究竟幹了些什麼，意思很明白擷取Httphandler。
那麼MvcRouteHandler是如何擷取一個Httphandler的了， 複製代碼 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MvcHandler執行個體。
最有一句context.RemapHandler(httpHandler); 很簡單很好明白吧，在HttpContext的RemapHandler方法中有這麼一句 this._remapHandler = handler;
在HttpContext中有這個屬性 複製代碼 代碼如下:internal IHttpHandler RemapHandlerInstance
{
get
{
return this._remapHandler;
}
}

那麼這個東西又是什麼時候調用的了，在HttpApplication的內部類MaterializeHandlerExecutionStep中的 void HttpApplication.IExecutionStep.Execute()方法調用 複製代碼 代碼如下:if (httpContext.RemapHandlerInstance != null)
{
httpContext.Handler = httpContext.RemapHandlerInstance;
}

看到MaterializeHandlerExecutionStep這個了類名，我想大家都能猜到吧。在內部類PipelineStepManager中BuildSteps方法有 複製代碼 代碼如下:HttpApplication.IExecutionStep step = new HttpApplication.MaterializeHandlerExecutionStep(app);
app.AddEventMapping("ManagedPipelineHandler", RequestNotification.MapRequestHandler, false, step);

我想大家看到這裡對mvc整個路由應該有個大致的理解了吧。