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

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

⑨接下来，就是HttpModules发挥作用的时候

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

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

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[]));
            }
            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。

ASP.NET MVC请求处理管道生命周期的19个关键环节系列包括：

ASP.NET MVC请求处理管道生命周期的19个关键环节(1-6)

ASP.NET MVC请求处理管道生命周期的19个关键环节(7-12)

ASP.NET MVC请求处理管道生命周期的19个关键环节(13-19)