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ASP.NET MVC请求处理管道生命周期的19个关键环节(7-12)

在上一篇"ASP.NET MVC请求处理管道生命周期的19个关键环节(1-6) ",体验了1-6关键环节,本篇继续。

 

  ⑦根据IsapiWorkerRequest对象,HttpRuntime创建HttpContext对象


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  ⑧HttpApplicationFactory创建新的或者从HttpApplication池获取现有的、可用的HttpApplication对象

HttpApplication的工作包括:

● 初始化的时候加载全部的HttpModule
● 接收请求
● 在不同阶段引发不同的事件,使得HttpModule通过订阅事件的方式加入到请求的处理过程中
● 在一个特定阶段获取一个IHttpHandler实例,最终将请求交给具体的IHttpHandler来实现

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  ⑨接下来,就是HttpModules发挥作用的时候


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所有的HttpModules都实现了IHttpModule接口:

public interface IHttpModule{  void Init(HttpApplication app);  void Dispose();}

可见,HttoModules正是由Init方法,根据传入的HttpApplication类型参数,订阅了HttpApplication的所有事件。

我们自定义一个HttpModule:

public class TestModule : IHttpModule{  public void Dispose(){}  public void Init(HttpApplication app)  {    app.PostAcquireRequestState += new EventHandler(app_PostAcuiredRequestState);    app.PreRequestHandlerExecute += new EventHandler(app_PreRequestHandlerExecute);  }  void app_PreRequestHandlerExecute(object sender, EventArgs e)  {    //TODO:  }  void app_PostAcquiredRequestState(object sender, EventArgs e)  {    //TODO:  }}

 

  ⑩当某个请求与一个规则匹配后,ASP.NET会调用匹配的HttpHandlerFactory的GetHandler方法来获取一个HttpHandler实例, 最后由一个HttpHandler实例来处理当前请求,生成响应内容


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所有的HttpHandlers都实现了IHttpHandler接口:

public interface IHttpHandler{  bool IsReusable{get;}  void ProcessRequest(HttpContext context);}

比如我们可以自定义一个HttpHandler来响应一类特定的请求:

public class Login : IHttpHandler{  public void ProcessRequest(HttpContext context)  {    context.Response.ContentType = "text/plain";    string username = context.Request.Form["name"];    string password = context.Request.Form["password"];    if(password="sth")    {      System.Web.Security.FormsAuthentication.SetAuthCookie(username, false);      context.Response.Write("ok");    }    else    {      context.Response.Write("用户名和密码不正确");    }  }}

 

⑾ASP.NET MVC的入口在UrlRoutingModule,即订阅了HttpApplication的第7个管道事件PostResolveRequestCahce,换句话说,是在HtttpApplication的第7个管道事件处对请求进行了拦截


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UrlRouteModlue实现了IHttpModule:

public class UrlRoutingModule : IHttpModule{    // Fields    private static readonly object _contextKey = new object();    private static readonly object _requestDataKey = new object();    private RouteCollection _routeCollection;     // Methods    protected virtual void Dispose()    {    }     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);    }     [Obsolete("This method is obsolete. Override the Init method to use the PostMapRequestHandler event.")]    public virtual void PostMapRequestHandler(HttpContextBase 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);                }            }        }    }     void IHttpModule.Dispose()    {        this.Dispose();    }     void IHttpModule.Init(HttpApplication application)    {        this.Init(application);    }     // Properties    public RouteCollection RouteCollection    {        get        {            if (this._routeCollection == null)            {                this._routeCollection = RouteTable.Routes;            }            return this._routeCollection;        }        set        {            this._routeCollection = value;        }    }}

UrlRoutingModule是在Web.config或默认的web.config中配置:

<httpModules>            ......            <add name="UrlRoutingModule-4.0" type="System.Web.Routing.UrlRoutingModule" />        </httpModules>

 

  ⑿而在请求到达UrlRoutingModule之前,我们在全局文件中做了如下配置

public class MvcApplication : System.Web.HttpApplication    {        protected void Application_Start()        {            ......            BundleConfig.RegisterBundles(BundleTable.Bundles);        }    }    public class RouteConfig    {        public static void RegisterRoutes(RouteCollection routes)        {            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");            routes.MapRoute(                name: "Default",                url: "{controller}/{action}/{id}",                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }            );        }    }

这意味着:在HttpApplication的第一个管道事件BeginRequest处,通过MapRoute()方法把路由注册到了RouteCollection中。在实际使用中,UrlRoutingModule是通过RouteTable的静态属性RouteCollection获取路由。

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未完待续~~