HttpModule对HttpApplication实例进行处理，而HttpApplication有很多事件（对应不同的生命期），这样就衍生出HttpModule内部事件机制和生命周期。
（1）、HttpModule的事件
BeginRequest 指示请求处理开始
AuthenticateRequest 封装请求身份验证过程
AuthorizeRequest 封装检查是否能利用以前缓存的输出页面处理请求的过程
ResolveRequestCache 从缓存中得到相应时候触发
AcquireRequestState 加载初始化Session时候触发
PreRequestHandlerExecute 在Http请求进入HttpHandler之前触发
PostRequestHandlerExecute 在Http请求进入HttpHandler之后触发
ReleaseRequestState 存储Session状态时候触发
UpdateRequestCache 更新缓存信息时触发
EndRequest 在Http请求处理完成的时候触发
PreSendRequestHenaders 在向客户端发送Header之前触发
PreSendRequestConternt 在向客户端发送内容之前触发
说明：
a、BenginRequest和EndRequest分别是HttpModule容器最开始的和最后的事件；
b、EndRequest之后还会触发PreSendRequestHeaders事件和PreSendRequestContent事件，这不是在HttpModule外的两个事件，表示HttpModule结束，即将开始向Client发送数据。
（2）、验证HttpModule生命周期
与HttpHandler的交互：
HttpModuleHandler
说明：
a、HttpModule容器会将HttpRequest传递到HttpHandler容器，这个时间点是ResolveRequestCache事件
b、HttpModule容器会建立HttpHandler实例作为入口——Session从此生效
c、触发AcquireRequestState事件以及PreRequestHandlerExecute事件
d、HttpModule容器便将对HttpRequest的控制权转让给HttpHandler容器
e、HttpHandler容器处理HttpRequest——使用自身的ProcessRequest方法，将对其控制权又还给HttpModule容器——之后Session失效。
验证生命周期代码：
using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
namespace MyHttpModule
{
public class ValidaterHttpModuleEvents : IHttpModule
{
public void Dispose()
{ }
/// <summary>
/// 验证HttpModule事件机制
/// </summary>
/// <param name="application"></param>
public void Init(HttpApplication application)
{
application.BeginRequest += new EventHandler(application_BeginRequest);
application.EndRequest += new EventHandler(application_EndRequest);
application.AcquireRequestState += new EventHandler(application_AcquireRequestState);
application.AuthenticateRequest += new EventHandler(application_AuthenticateRequest);
application.AuthorizeRequest += new EventHandler(application_AuthorizeRequest);
application.PreRequestHandlerExecute += new EventHandler(application_PreRequestHandlerExecute);
application.PostRequestHandlerExecute += new EventHandler(application_PostRequestHandlerExecute);
application.ReleaseRequestState += new EventHandler(application_ReleaseRequestState);
application.ResolveRequestCache += new EventHandler(application_ResolveRequestCache);
application.PreSendRequestHeaders += new EventHandler(application_PreSendRequestHeaders);
application.PreSendRequestContent += new EventHandler(application_PreSendRequestContent);
}
private void application_BeginRequest(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_BeginRequest<br/>");
}
private void application_EndRequest(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_EndRequest<br/>");
}
private void application_PreRequestHandlerExecute(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_PreRequestHandlerExecute<br/>");
}
private void application_PostRequestHandlerExecute(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_PostRequestHandlerExecute<br/>");
}
private void application_ReleaseRequestState(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_ReleaseRequestState<br/>");
}
private void application_AcquireRequestState(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_AcquireRequestState<br/>");
}
private void application_PreSendRequestContent(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_PreSendRequestContent<br/>");
}
private void application_PreSendRequestHeaders(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_PreSendRequestHeaders<br/>");
}
private void application_ResolveRequestCache(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_ResolveRequestCache<br/>");
}
private void application_AuthorizeRequest(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_AuthorizeRequest<br/>");
}
private void application_AuthenticateRequest(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
application.Context.Response.Write("application_AuthenticateRequest<br/>");
}
}
}
<add name="HttpModule1" type="MyHttpModule.HttpModule1,MyHttpModule"/> <add name="HttpModule2" type="MyHttpModule.HttpModule2,MyHttpModule"/>
HttpModule1和HttpModule2模仿ValidaterHttpModuleEvents编写（除了类名改变外，事件和方法不变），不贴代码了。运行结果如下：
HttpModuleCompare
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。
(3)、利用HttpModule实现终止此次HttpRequest请求
在BeginRequest事件中，使用HttpApplication.CompleteRequest()方法可以实现当满足一定条件时终止此次HttpRequest请求
using System;
using System.Web;
namespace ClassLibrary1
{
public class MyHttpModule : IHttpModule
{
public void Dispose() { }
public void Init(HttpApplication context)
{
context.BeginRequest += new EventHandler(Application_BeginRequest);
}
public void Application_BeginRequest(object sender, EventArgs e)
{
HttpApplication application = sender as HttpApplication;
application.CompleteRequest();
application.Context.Response.Write("请求被终止");
}
}
}
说明：
a、对于一个HttpModule，在BeginRquest中终止，但是仍然会调用EndRequest事件，以及 PreSendRequestHeaders事件和PreSendRequestContent事件。也可以说是直接跳转到EndRequest事件，而 不会调用这期间的事件
b、如果有两个HttpModule，在第一个HttpModule的BeginRequest中终止，仅仅不会调用第二 个HttpModule的BeginRequest，但仍然会调用两个EndRequest事件，以及PreSendRequestHeaders事件和 PreSendRequestContent事件。
