IHttpModule的那些事

写在前面

关于IHttpModule的相关内容，在面试的时候也被问到过，当时也是隐隐约约的感觉这个接口有一个Init方法，可以在实现类中的Init方法注册一系列的事件，说句实话，具体哪些事件，忘了差不多了。今天周末在家，也确实没什么事，就算是对这块知识进行查漏补缺了。

IHttpModule工作方式

熟悉asp.net生命周期的朋友，应该知道HttpModule的执行是在HttpHandler之前被执行，执行HttpModule的一系列事件后然后执行HttpHandler，然后又执行HttpModule的一些事件。具体的可以参考下面的生命周期的图。

而HttpHandler才是处理http请求的地方，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。

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。

一个实例

项目结构

MyHttpModule代码

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;

 namespace MyHttpModule
 {
     /// <summary>
     /// 自定义HttpModule
     /// </summary>
     public class MyHttpModule : IHttpModule
     {
         public void Dispose()
         {
             throw new NotImplementedException();
         }

         public void Init(HttpApplication context)
         {
             context.BeginRequest += context_BeginRequest;
             context.EndRequest += context_EndRequest;
         }

         void context_EndRequest(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的EndRequest");

             }
         }

         void context_BeginRequest(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的BeginRequest");

             }
         }
     }
 }

在web.config注册自定义的HttpModule

 <?xml version="1.0" encoding="utf-8"?>
 <!--
   For more information on how to configure your ASP.NET application, please visit
   http://go.microsoft.com/fwlink/?LinkId=169433
   -->
 <configuration>
   <system.web>
     <compilation debug="true" targetFramework="4.5" />
     <httpRuntime targetFramework="4.5" />

   </system.web>
   <system.webServer>
     <modules>
       <add name="MyHttpModule" type="MyHttpModule.MyHttpModule,MyHttpModule"/>
     </modules>
   </system.webServer>
 </configuration>

浏览页面Default.aspx

那么在生命周期过程中的一系列的事件的执行顺序是怎样的呢？

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;

 namespace MyHttpModule
 {
     /// <summary>
     /// 自定义HttpModule
     /// </summary>
     public class MyHttpModule : IHttpModule
     {
         public void Dispose()
         {
             throw new NotImplementedException();
         }

         public void Init(HttpApplication context)
         {
             context.BeginRequest += context_BeginRequest;
             context.EndRequest += context_EndRequest;
             context.PostAcquireRequestState += context_PostAcquireRequestState;
             context.PostAuthenticateRequest += context_PostAuthenticateRequest;
             context.PostAuthorizeRequest += context_PostAuthorizeRequest;
             context.PostLogRequest += context_PostLogRequest;
             context.PostMapRequestHandler += context_PostMapRequestHandler;
             context.PostRequestHandlerExecute += context_PostRequestHandlerExecute;
             context.PostResolveRequestCache += context_PostResolveRequestCache;
             context.PostUpdateRequestCache += context_PostUpdateRequestCache;
             context.PreRequestHandlerExecute += context_PreRequestHandlerExecute;
             context.PreSendRequestContent += context_PreSendRequestContent;
             context.PreSendRequestHeaders += context_PreSendRequestHeaders;
             context.RequestCompleted += context_RequestCompleted;
             context.ResolveRequestCache += context_ResolveRequestCache;
             context.UpdateRequestCache += context_UpdateRequestCache;
             context.ReleaseRequestState += context_ReleaseRequestState;
         }

         void context_UpdateRequestCache(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的UpdateRequestCache<br/>");
             }
         }

         void context_ResolveRequestCache(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的ResolveRequestCache<br/>");
             }
         }

         void context_RequestCompleted(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的RequestCompleted<br/>");
             }
         }

         void context_PreSendRequestHeaders(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PreSendRequestHeaders<br/>");
             }
         }

         void context_PreSendRequestContent(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PreSendRequestContent<br/>");
             }
         }

         void context_PreRequestHandlerExecute(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PreRequestHandlerExecute<br/>");
             }
         }

         void context_PostUpdateRequestCache(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostUpdateRequestCache<br/>");
             }
         }

         void context_PostResolveRequestCache(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostResolveRequestCache<br/>");
             }
         }

         void context_PostRequestHandlerExecute(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostRequestHandlerExecut<br/>");
             }
         }

         void context_PostMapRequestHandler(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostMapRequestHandler<br/>");
             }
         }

         void context_PostLogRequest(object sender, EventArgs e)
         {
               HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostLogRequest<br/>");
             }
         }

         void context_PostAuthorizeRequest(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostAuthorizeRequest<br/>");
             }
         }

         void context_PostAuthenticateRequest(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostAuthenticateRequest<br/>");
             }
         }

         void context_PostAcquireRequestState(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的PostAcquireRequestState<br/>");
             }
         }

         void context_ReleaseRequestState(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的ReleaseRequestState<br/>");
             }
         }

         void context_EndRequest(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的EndRequest<br/>");
             }
         }

         void context_BeginRequest(object sender, EventArgs e)
         {
             HttpApplication app = sender as HttpApplication;
             if (app != null)
             {
                 HttpContext context = app.Context;
                 HttpResponse response = app.Response;
                 response.Write("自定义HttpModule中的BeginRequest<br/>");

             }
         }
     }
 }

浏览结果

使用HttpModule终止此次Http请求

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using System.Web;
 namespace MyHttpModule
 {
     public class EndModule : IHttpModule
     {
         public void Dispose()
         {
             throw new NotImplementedException();
         }

         public void Init(HttpApplication context)
         {
             context.BeginRequest += context_BeginRequest;
         }

         void context_BeginRequest(object sender, EventArgs e)
         {
             HttpApplication application = (HttpApplication)sender;

             application.CompleteRequest();

             application.Context.Response.Write("请求被终止。");

         }
     }
 }

结果

总结

这里介绍了在asp.net生命周期中一个最重要的接口IHttpModule，可以这样来形容该接口，事件接口，因为在实现类中的Init方法中，可以注册生命周期中的各种事件，并可以在事件中定义各种逻辑。

参考文章

一点一点学ASP.NET之基础概念——HttpModule 文野