HttpModule是如何工作的

當一個HTTP請求到達HttpModule時，整個ASP.NET Framework系統還并沒有對這個HTTP請求做任何處理，也就是說此時對于HTTP請求來講，HttpModule是一個HTTP請求的“必經之路”，所以可以在這個HTTP請求傳遞到真正的請求處理中心（HttpHandler）之前附加一些需要的信息在這個HTTP請求信息之上，或者針對截獲的這個HTTP請求信息作一些額外的工作，或者在某些情況下干脆終止滿足一些條件的HTTP請求，從而可以起到一個Filter過濾器的作用。

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示例1：

using System;

using System.Collections.Generic;

using System.Text;

using System.Web;

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namespace MyHttpModule

{

???? /// <summary>

???? /// 說明：用來實現自己的HttpModule類。

???? /// 作者：文野

???? /// 聯系：stwyhm@cnblogs.com

???? /// </summary>

???? public class MyFirstHttpModule : IHttpModule

???? {

???????? private void Application_BeginRequest(object sender, EventArgs e)

???????? {

????????????? HttpApplication application = (HttpApplication)sender;

????????????? HttpContext context = application.Context;

????????????? HttpRequest request = application.Request;

????????????? HttpResponse response = application.Response;

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????????????? response.Write("我來自自定義HttpModule中的BeginRequest<br />");

???????? }

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???????? private void Application_EndRequest(object sender, EventArgs e)

???????? {

????????????? HttpApplication application = (HttpApplication)sender;

????????????? HttpContext context = application.Context;

????????????? HttpRequest request = application.Request;

????????????? HttpResponse response = application.Response;

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????????????? response.Write("我來自自定義HttpModule中的EndRequest<br />");

???????? }

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???????? #region IHttpModule 成員

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???????? public void Dispose()

???????? {}

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???????? public void Init(HttpApplication application)

???????? {

????????????? application.BeginRequest += new EventHandler(Application_BeginRequest);

????????????? application.EndRequest += new EventHandler(Application_EndRequest);

???????? }

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???????? #endregion

???? }

}

在Web.config進行如下配置

<add name="MyFirstHttpModule" type="MyHttpModule.MyFirstHttpModule,MyHttpModule"/>

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深入了解HttpModule

一個HTTP請求在HttpModule容器的傳遞過程中，會在某一時刻（ResolveRequestCache事件）將這個HTTP請求傳遞給HttpHandler容器。在這個事件之后，HttpModule容器會建立一個HttpHandler的入口實例，但是此時并沒有將HTTP請求控制權交出，而是繼續觸發AcquireRequestState事件以及PreRequestHandlerExcute事件。在PreRequestHandlerExcute事件之后，HttpModule窗口就會將控制權暫時交給HttpHandler容器，以便進行真正的HTTP請求處理工作。

而在HttpHandler容器內部會執行ProcessRequest方法來處理HTTP請求。在容器HttpHandler處理完畢整個HTTP請求之后，會將控制權交還給HttpModule，HttpModule則會繼續對處理完畢的HTTP請求信息流進行層層的轉交動作，直到返回到客戶端為止。

圖1：HttpModule生命周期示意圖

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示例2：驗證HttpModule生命周期

using System;

using System.Collections.Generic;

using System.Text;

using System.Web;

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namespace MyHttpModule

{

??? public class ValidaterHttpModule : IHttpModule

??? {

??????? #region IHttpModule 成員

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??????? public void Dispose()

??????? {}

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??????? public void Init(HttpApplication application)

??????? {

??????????? application.BeginRequest += new EventHandler(application_BeginRequest);

??????????? application.EndRequest += new EventHandler(application_EndRequest);

??????????? application.PreRequestHandlerExecute += new EventHandler(application_PreRequestHandlerExecute);

??????????? application.PostRequestHandlerExecute += new EventHandler(application_PostRequestHandlerExecute);

??????????? application.ReleaseRequestState += new EventHandler(application_ReleaseRequestState);

??????????? application.AcquireRequestState += new EventHandler(application_AcquireRequestState);

??????????? application.AuthenticateRequest += new EventHandler(application_AuthenticateRequest);

??????????? application.AuthorizeRequest += new EventHandler(application_AuthorizeRequest);

??????????? application.ResolveRequestCache += new EventHandler(application_ResolveRequestCache);

??????????? application.PreSendRequestHeaders += new EventHandler(application_PreSendRequestHeaders);

?????????? ?application.PreSendRequestContent += new EventHandler(application_PreSendRequestContent);

??????? }

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??????? void application_PreSendRequestContent(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

? ??????????application.Context.Response.Write("application_PreSendRequestContent<br/>");

??????? }

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??????? void application_PreSendRequestHeaders(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

???? ???????application.Context.Response.Write("application_PreSendRequestHeaders<br/>");

??????? }

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??????? void application_ResolveRequestCache(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

????????? ??application.Context.Response.Write("application_ResolveRequestCache<br/>");

??????? }

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??????? void application_AuthorizeRequest(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

??????????? application.Context.Response.Write("application_AuthorizeRequest<br/>");

??????? }

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??????? void application_AuthenticateRequest(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

??????????? application.Context.Response.Write("application_AuthenticateRequest<br/>");

??????? }

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??????? void application_AcquireRequestState(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

??????????? application.Context.Response.Write("application_AcquireRequestState<br/>");

??????? }

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??????? void application_ReleaseRequestState(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

??????????? application.Context.Response.Write("application_ReleaseRequestState<br/>");

??????? }

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??????? void application_PostRequestHandlerExecute(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

??????????? application.Context.Response.Write("application_PostRequestHandlerExecute<br/>");

??????? }

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??????? void application_PreRequestHandlerExecute(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

??????????? application.Context.Response.Write("application_PreRequestHandlerExecute<br/>");

??????? }

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??????? void application_EndRequest(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

?????? ?????application.Context.Response.Write("application_EndRequest<br/>");

??????? }

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??????? void application_BeginRequest(object sender, EventArgs e)

??????? {

??????????? HttpApplication application = (HttpApplication)sender;

??????????? application.Context.Response.Write("application_BeginRequest<br/>");

??????? }

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???????

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??????? #endregion

??? }

}

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多個自定義的Http Module的運作

從運行結果可以看到，在web.config文件中引入自定義HttpModule的順序就決定了多個自定義HttpModule在處理一個HTTP請求的接管順序。注：系統默認那幾個HttpModule是最先衩ASP.NET Framework所加載上去的。

示例3：（代碼類同示例2）

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在HttpModule中終止此次的HTTP請求

可以利用HttpModule通過調用HttpApplication.CompleteRequest()方法實現當滿足某一個條件時終止此次的HTTP請求。

需要注意的是，即使調用了HttpApplication.CompleteRequest()方法終止了一個HTTP請求，ASP.NET Framework仍然會觸發HttpApplication后面的這3個事件：EndRequest事件、PreSendRequestHeaders事件、PreSendRequestContent事件。

如果存在多個自定義的HttpModule的話，當Module1終止了一個HTTP請求，這個HTTP請求將不會再觸發Module2中相應的事件了，但Module2的最后三個事件仍會被觸發。

示例4：

using System;

using System.Collections.Generic;

using System.Text;

using System.Web;

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namespace MyHttpModule

{

??? public class CompleteRequestHttpModule : IHttpModule

??? {

??????? #region IHttpModule 成員

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??????? public void Dispose()

??????? {}

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??????? public void Init(HttpApplication application)

??????? {

??????????? application.BeginRequest += new EventHandler(Application_BeginRequest);

??????? }

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??????? void Application_BeginRequest(object sender, EventArgs e)

??????? {

????????? ??HttpApplication application = (HttpApplication)sender;

??????????? application.CompleteRequest();

??????????? application.Context.Response.Write("請求被終止。");

??????? }

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??????? #endregion

??? }

}

轉載于:https://www.cnblogs.com/systemxgl/archive/2009/09/08/1562416.html

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