Asp.net MVC Route初探

Asp.net MVC天生就有着漂亮的Url.但是却有别于Asp.net的UrlRewriter.那么其的实现原理是怎样的呢?这就要说到Route了.

Asp.Net MVC生命周期

Asp.net MVC的生命周期由8个步骤组成:

1.RouteTable(路由表)的创建

2.UrlRoutingMoudle请求拦截

3.Routing engine确定route

4.RouteHandler创建相关的IHttpHandler实例

5.IHttpHandler实例确定Controller(控制器)

6.Controller执行

7.视图引擎创建

8.视图呈现

这里主要讲解前4个.

RouteTable(路由表)的创建

打开Global.asax

public class MvcApplication : System.Web.HttpApplication
   {
       public static void RegisterRoutes(RouteCollection routes)
       {
           routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

           routes.MapRoute(
               "Default", // Route name
               "{controller}/{action}/{id}", // URL with parameters
               new { controller = "Home", action = "Index", id = UrlParameter.Optional }, // Parameter defaults
               new { controller = @"[^\.]*"}
           );

           routes.MapRoute(
               "Defalut",
               "{controller}/Blog/{date}",
               new {  action = "Blog" },
               new { date = @"^\d{4}\.\d{2}\.\d{2}" }
               );
       }

       protected void Application_Start()
       {
           AreaRegistration.RegisterAllAreas();

           RegisterRoutes(RouteTable.Routes);

           //RouteDebug.RouteDebugger.RewriteRoutesForTesting(RouteTable.Routes);
       }
   }

在此,我们声明了两个Route.

在MVC1中.我们必须

routes.Add(new Route("User/Login", new RouteValueDictionary(new { controller = "User", action = "Login" }), new MvcRouteHandler()));
           routes.Add(new Route("User/Logout", new RouteValueDictionary(new { controller = "User", action = "Logout" }), new MvcRouteHandler()));
           routes.Add(new Route("User/Signup", new RouteValueDictionary(new { controller = "User", action = "Signup" }), new MvcRouteHandler()));

 

这样添加.但在.Net3.5中.我们却可以直接利用匿名类直接New一个.这是因为.Net3.5中扩展了一个MapRoute方法.该方法利用反射.进行背后的添加

public static Route MapRoute(this RouteCollection routes, string name, string url, object defaults, object constraints, string[] namespaces) {
            if (routes == null) {
                throw new ArgumentNullException("routes");
            }
            if (url == null) {
                throw new ArgumentNullException("url");
            }

            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;
        }

 

UrlRoutingMoudle请求拦截

按照MS惯例,一般会在WebConfig留下些蛛丝马迹,打开WebConfig.不出其然.我们发现HttpMoudle中有

<add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, System.Web.Routing, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>

利用Reflector打开UrlRoutingModule类.

protected virtual void Init(HttpApplication application)
{
    application.PostResolveRequestCache += new EventHandler(this.OnApplicationPostResolveRequestCache);
    application.PostMapRequestHandler += new EventHandler(this.OnApplicationPostMapRequestHandler);
}

Routing engine确定route

可以看到.在application的events中注册了PostResolveRequestCache 和PostMapRequestHandler 事件.

PostResolveRequestCache

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, RoutingResources.UrlRoutingModule_NoRouteHandler, new object[0]));
        }
        if (!(routeHandler is StopRoutingHandler))
        {
            RequestContext requestContext = new RequestContext(context, routeData);
            IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);
            if (httpHandler == null)
            {
                throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, RoutingResources.UrlRoutingModule_NoHttpHandler, new object[] { routeHandler.GetType() }));
            }
            context.Items[_requestDataKey] = new RequestData { OriginalPath = context.Request.Path, HttpHandler = httpHandler };
            context.RewritePath("~/UrlRouting.axd");
        }
    }
}

这里.首先通过RouteCollection.GetRouteData得到当前的RouteData,

UrlRoutingModule.RouteCollection

public RouteCollection RouteCollection
{
    get
    {
        if (this._routeCollection == null)
        {
            this._routeCollection = RouteTable.Routes;
        }
        return this._routeCollection;
    }
    set
    {
        this._routeCollection = value;
    }
}

module中的RouteCollection只是很简单的引用了RouteTable中的静态实例Routes而已.

RouteTable

public class RouteTable
{
    // Fields
    private static RouteCollection _instance = new RouteCollection();

    // Properties
    public static RouteCollection Routes
    {
        get
        {
            return _instance;
        }
    }
}

RouteCollection.GetRouteData

这是获取RouteDate的核心实现.

public RouteData GetRouteData(HttpContextBase httpContext)
{
    if (httpContext == null)
    {
        throw new ArgumentNullException("httpContext");
    }
    if (httpContext.Request == null)
    {
        throw new ArgumentException(RoutingResources.RouteTable_ContextMissingRequest, "httpContext");
    }
    if (!this.RouteExistingFiles)
    {
        string appRelativeCurrentExecutionFilePath = httpContext.Request.AppRelativeCurrentExecutionFilePath;
        if (((appRelativeCurrentExecutionFilePath != "~/") && (this._vpp != null)) && (this._vpp.FileExists(appRelativeCurrentExecutionFilePath) || this._vpp.DirectoryExists(appRelativeCurrentExecutionFilePath)))
        {
            return null;
        }
    }
    using (this.GetReadLock())//线程锁
    {
        foreach (RouteBase base2 in this)//遍历当前集合中的所有RouteBase
        {
            RouteData routeData = base2.GetRouteData(httpContext); //调用RouteBase的RouteData.此处传入的Class是Route.
            if (routeData != null)
            {
                return routeData;
            }
        }
    }
    return null;
}

Route

Route继承至RouteBase.Route中提供了MVC的Route信息.

可以看到最后承载Route数据的容器是RouteVallueDictionary.Route中包含了该Dictionary

RouteData

RouteData的实现很简单.就提供了几个基本的字段而已.主要用于描述当前Route数据的信息.如此一来.我们可以得到当前Url所匹配的Route.

public class RouteData
{
    // Fields
    private RouteValueDictionary _dataTokens;
    private IRouteHandler _routeHandler;
    private RouteValueDictionary _values;

    // Methods
    public RouteData();
    public RouteData(RouteBase route, IRouteHandler routeHandler);
    public string GetRequiredString(string valueName);

    // Properties
    public RouteValueDictionary DataTokens { get; }
    public RouteBase Route { get; set; }
    public IRouteHandler RouteHandler { get; set; }
    public RouteValueDictionary Values { get; }
}

RouteHandler创建相关的IHttpHandler实例

RouteHandler

得到RouteData之后.获取RouteData之中的RouteHandler.根据RouteHandler获取相关的IHttpHandler.这样.MVC的Route隐射阶段就已经完成

RequestContext requestContext = new RequestContext(context, routeData);
IHttpHandler httpHandler = routeHandler.GetHttpHandler(requestContext);

 

后面就是Controller的确定和执行了.