学习是使用asp.net已经有很长一段时间了，现在就来分析一下mvc的整过过程吧。个人计划写一个mvc系列的博文，仅从源代码的角度来分析mvc。在接触mvc时我们一定会经历路由，那么路由这东东是怎么搞出来的啊。在我们的web.config中有这么一句： <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /> 看来路由是它咋负责了。在这个dll中有一个很特殊的类UrlRoutingModule
我们来看看它里面主要的核心代码吧：
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
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
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？
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
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：
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：
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，
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
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
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
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。