ASP.NET中的HttpModule

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：[email protected]
     /// </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
    }
}

转载于：http://www.cnblogs.com/stwyhm/archive/2006/08/09/471729.html