HttpModule是如何工作的 当一个HTTP请求到达HttpModule时，整个ASP.NET Framework系统还并没有对这个HTTP请求做任何处理，也就是说此时对于HTTP请求来讲，HttpModule是一个HTTP请求的“必经之路”，所以可以在这个HTTP请求传递到真正的请求处理中心（HttpHandler）之前附加一些需要的信息在这个HTTP请求信息之上，或者针对截获的这个HTTP请求信息作一些额外的工作，或者在某些情况下干脆终止满足一些条件的HTTP请求，从而可以起到一个Filter过滤器的作用。 示例1： using System; using System.Collections.Generic; using System.Text; using System.Web; namespace MyHttpModule {      /// <summary>      /// 说明：用来实现自己的HttpModule类。      /// 作者：文野      /// 联系：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;               response.Write("我来自自定义HttpModule中的BeginRequest<br />");          }          private void Application_EndRequest(object sender, EventArgs e)          {               HttpApplication application = (HttpApplication)sender;               HttpContext context = application.Context;               HttpRequest request = application.Request;               HttpResponse response = application.Response;               response.Write("我来自自定义HttpModule中的EndRequest<br />");          }          #region IHttpModule 成员          public void Dispose()          {}          public void Init(HttpApplication application)          {               application.BeginRequest += new EventHandler(Application_BeginRequest);               application.EndRequest += new EventHandler(Application_EndRequest);          }          #endregion      } } 在Web.config进行如下配置 <add name="MyFirstHttpModule" type="MyHttpModule.MyFirstHttpModule,MyHttpModule"/> 深入了解HttpModule 一个HTTP请求在HttpModule容器的传递过程中，会在某一时刻（ResolveRequestCache事件）将这个HTTP请求传递给HttpHandler容器。在这个事件之后，HttpModule容器会建立一个HttpHandler的入口实例，但是此时并没有将HTTP请求控制权交出，而是继续触发AcquireRequestState事件以及PreRequestHandlerExcute事件。在PreRequestHandlerExcute事件之后，HttpModule窗口就会将控制权暂时交给HttpHandler容器，以便进行真正的HTTP请求处理工作。 而在HttpHandler容器内部会执行ProcessRequest方法来处理HTTP请求。在容器HttpHandler处理完毕整个HTTP请求之后，会将控制权交还给HttpModule，HttpModule则会继续对处理完毕的HTTP请求信息流进行层层的转交动作，直到返回到客户端为止。 图1：HttpModule生命周期示意图 示例2：验证HttpModule生命周期 using System; using System.Collections.Generic; using System.Text; using System.Web; namespace MyHttpModule {     public class ValidaterHttpModule : IHttpModule     {         #region IHttpModule 成员         public void Dispose()         {}         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);         }         void application_PreSendRequestContent(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_PreSendRequestContent<br/>");         }         void application_PreSendRequestHeaders(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_PreSendRequestHeaders<br/>");         }         void application_ResolveRequestCache(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_ResolveRequestCache<br/>");         }         void application_AuthorizeRequest(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_AuthorizeRequest<br/>");         }         void application_AuthenticateRequest(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_AuthenticateRequest<br/>");         }         void application_AcquireRequestState(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_AcquireRequestState<br/>");         }         void application_ReleaseRequestState(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_ReleaseRequestState<br/>");         }         void application_PostRequestHandlerExecute(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_PostRequestHandlerExecute<br/>");         }         void application_PreRequestHandlerExecute(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_PreRequestHandlerExecute<br/>");         }         void application_EndRequest(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_EndRequest<br/>");         }         void application_BeginRequest(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.Context.Response.Write("application_BeginRequest<br/>");         }                 #endregion     } } 多个自定义的Http Module的运作 从运行结果可以看到，在web.config文件中引入自定义HttpModule的顺序就决定了多个自定义HttpModule在处理一个HTTP请求的接管顺序。注：系统默认那几个HttpModule是最先衩ASP.NET Framework所加载上去的。 示例3：（代码类同示例2） 在HttpModule中终止此次的HTTP请求 可以利用HttpModule通过调用HttpApplication.CompleteRequest()方法实现当满足某一个条件时终止此次的HTTP请求。 需要注意的是，即使调用了HttpApplication.CompleteRequest()方法终止了一个HTTP请求，ASP.NET Framework仍然会触发HttpApplication后面的这3个事件：EndRequest事件、PreSendRequestHeaders事件、PreSendRequestContent事件。 如果存在多个自定义的HttpModule的话，当Module1终止了一个HTTP请求，这个HTTP请求将不会再触发Module2中相应的事件了，但Module2的最后三个事件仍会被触发。 示例4： using System; using System.Collections.Generic; using System.Text; using System.Web; namespace MyHttpModule {     public class CompleteRequestHttpModule : IHttpModule     {         #region IHttpModule 成员         public void Dispose()        {}         public void Init(HttpApplication application)         {             application.BeginRequest += new EventHandler(Application_BeginRequest);         }         void Application_BeginRequest(object sender, EventArgs e)         {             HttpApplication application = (HttpApplication)sender;             application.CompleteRequest();             application.Context.Response.Write("请求被终止。");         }         #endregion     } }

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