HttpApplication,HttpModule,HttpContext及Asp.Net页生命周期
摘要：强烈推荐ASP.NET入门者看这些知识点，因为不管学什么技术，了解它的原理是非常重要的。虽然你平时code的时候看不见它的踪影，但它是一直存在的。
[1] HttpApplication,HttpModule,HttpContext及Asp.Net页生命周期[2] HttpApplication,HttpModule,HttpContext及Asp.Net页生命周期
Modules:每一个实现了IHttpModule接口的类，就可以被认为是Http模块组件，可以理解为http请求拦截器，拦截到http请求后，它能修改正在被处理的Context上下文，完事儿之后，再把控制权交还给管道，如果还有其它模块，则依次继续处理，直到所有Modules集合中的HttpModule都“爽”完为止(注：可怜的http请求就这样给各个httpModule轮X了)
asp.net2.0默认内置了很多HttpModule，从Machine.Config文件中可以发现以下默认的内置模块：
AnonymouseIdentification --为匿名用户分配一个临时身份
FileAuthorization --验证用户是否有请求文件的Windows NT许可
FormsAuthentication --窗体身份验证模块(如果没有这个模块,asp.net就无法以用户名/密码[即FOrms]方式验证)
OutputCache --输出缓存模块
PassportAuthentication --PassPort验证模块
Profile --用户配置模块(如果没有它，asp.net中就无法使用Profile)
RoleManager --角色管理
SessionSate --会话状态模块
UrlAuthorization --基于URL的身份验证模块
WindowsAuthentication --Windows和IIS身份验证模块
User：如果您使用过asp.net2.0内置的Membership/Role机制来进行访问认证，就会对User对象感到很熟悉，比如：
if (HttpContext.Current.User.Identity.IsAuthenticated)
{
//用户登录过了...
}
我们常用它来判断当前浏览用户的登录状态，关于User类的更详细定义，可参见MSDN。
生命周期：最后再来回顾一下Asp.Net中Page页的生命周期，Page中定义了几个事件：
总体上讲：一个ASPX页面被请求时，最终的生命周期就是由Page中定义的上述事件(还有一些可重载的回调方法)以及以前提到的HttpApplication类中定义的事件(以相应的回调方法)共同触发或调用，最终叠加形成的一连串处理过程。
如果先不考虑HttpApplication中的事件处理方法(即不考虑我们在Global.ascx.cs中定义的Application_XXX处理方法)，Page中的事件(方法)常规触发(调用)顺序为：
01.Page_PreInit
02.Page_Init
03.Page_InitComplete
04.Page_PreLoad
05.Page_Load
06.Page_LoadComplete
07.Page_PreRender
08.Page_SaveStateComplete
09.Page_Unload
这是在Page页面未回发，且不考虑页面子控件的前提下正常的顺序，如果加入页面回发(比如在页面中放一个asp:Button，然后在Button的Click回发事件中加入处理函数)后，顺序稍微有些变化：
01.Page_PreInit
02.Page_Init
03.Page_InitComplete
04.Page_PreLoad
05.Page_Load
06.Button1_Click
07.Page_LoadComplete
08.Page_PreRender
09.Page_SaveStateComplete
10.Page_Unload
不同的地方在于：回发事件Button1_Click在Page_Load后被触发。
最后再把HttpApplication的事件考虑进来，看下叠加后的顺序，不过先别着急，我们先来看一种特殊情况，如果一个asp.net应用根目录下未设置默认页，这时直接浏览根目录，比如http://localhost:2345/ 时，Globl.ascx.cs中定义的Application_XXX方法的调用顺序如下：
2010-03-28 15:01:39 413 Application_Start
2010-03-28 15:01:39 491 Init
2010-03-28 15:01:39 491 Application_BeginRequest
2010-03-28 15:01:39 506 Application_AuthenticateRequest
2010-03-28 15:01:39 506 Application_PostAuthenticateRequest
2010-03-28 15:01:39 506 Application_AuthorizeRequest
2010-03-28 15:01:39 522 Application_PostAuthorizeRequest
2010-03-28 15:01:39 522 Application_ResolveRequestCache
2010-03-28 15:01:39 522 Application_PostResolveRequestCache
2010-03-28 15:01:39 522 Application_PostMapRequestHandler
2010-03-28 15:01:39 522 Application_AcquireRequestState
2010-03-28 15:01:39 537 Application_PostAcquireRequestState
2010-03-28 15:01:39 537 Application_PreRequestHandlerExecute
2010-03-28 15:01:39 553 Application_Error
2010-03-28 15:01:39 553 Application_EndRequest
2010-03-28 15:01:39 569 Application_PreSendRequestHeaders
2010-03-28 15:01:39 569 Application_PreSendRequestContent
可以看到会触发Application_Error事件，即HttpRuntime认为这是一个错误，紧接着再浏览一个实际存在的页面，如果这时应用程序有严重错误，导致Application关闭(比如web.config配置错误)，调用的顺序如下：
2010-03-28 15:03:47 704 Application_BeginRequest
2010-03-28 15:03:47 704 Application_AuthenticateRequest
2010-03-28 15:03:47 766 Application_PostAuthenticateRequest
2010-03-28 15:03:47 766 Application_AuthorizeRequest
2010-03-28 15:03:47 766 Application_PostAuthorizeRequest
2010-03-28 15:03:47 766 Application_ResolveRequestCache
2010-03-28 15:03:47 783 Application_PostResolveRequestCache
2010-03-28 15:03:48 667 Application_PostMapRequestHandler
2010-03-28 15:03:48 667 Application_AcquireRequestState
2010-03-28 15:03:48 683 Application_PostAcquireRequestState
2010-03-28 15:03:48 698 Application_PreRequestHandlerExecute
2010-03-28 15:03:48 745 Page_PreInit
2010-03-28 15:04:02 903 Page_Unload
2010-03-28 15:04:02 903 Application_Error
2010-03-28 15:04:02 918 Application_EndRequest
2010-03-28 15:04:02 996 Application_PreSendRequestHeaders
2010-03-28 15:04:02 996 Application_PreSendRequestContent
2010-03-28 15:04:03 371 Application_Disposed
2010-03-28 15:04:03 371 Dispose
2010-03-28 15:04:03 386 Application_End
对比刚才的顺序，会发现Application_Start及Init没有再次被调用，也印证了文章前面提到的一些结论(Application_Start在整个asp.net应用生命周期内只触发一次)，而且从最后的三个输出能知道：应用程序关闭时Application_Disposed,Dispose,Application_End按顺序调用。
再"重新"浏览(指web Server重启)一下正常访问的页面，在不出错也不回发的情况下，顺序如下：
2010-03-28 15:08:11 513 Application_Start
2010-03-28 15:08:11 591 Init
2010-03-28 15:08:11 591 Application_BeginRequest
2010-03-28 15:08:11 591 Application_AuthenticateRequest
2010-03-28 15:08:11 591 Application_PostAuthenticateRequest
2010-03-28 15:08:11 606 Application_AuthorizeRequest
2010-03-28 15:08:11 606 Application_PostAuthorizeRequest
2010-03-28 15:08:11 606 Application_ResolveRequestCache
2010-03-28 15:08:11 606 Application_PostResolveRequestCache
2010-03-28 15:08:11 622 Application_PostMapRequestHandler
2010-03-28 15:08:11 637 Application_EndRequest
2010-03-28 15:08:11 637 Application_PreSendRequestHeaders
2010-03-28 15:08:11 637 Application_PreSendRequestContent
2010-03-28 15:08:11 637 Application_BeginRequest
2010-03-28 15:08:11 637 Application_AuthenticateRequest
2010-03-28 15:08:11 653 Application_PostAuthenticateRequest
2010-03-28 15:08:11 653 Application_AuthorizeRequest
2010-03-28 15:08:11 653 Application_PostAuthorizeRequest
2010-03-28 15:08:11 653 Application_ResolveRequestCache
2010-03-28 15:08:11 653 Application_PostResolveRequestCache
2010-03-28 15:08:11 653 Application_PostMapRequestHandler
2010-03-28 15:08:11 653 Session_Start
2010-03-28 15:08:11 653 Application_AcquireRequestState
2010-03-28 15:08:11 653 Application_PostAcquireRequestState
2010-03-28 15:08:11 653 Application_PreRequestHandlerExecute
2010-03-28 15:08:11 669 Page_PreInit
2010-03-28 15:08:11 684 Page_Init
2010-03-28 15:08:11 684 Page_InitComplete
2010-03-28 15:08:11 684 Page_PreLoad
2010-03-28 15:08:11 684 Page_Load
2010-03-28 15:08:11 684 Page_LoadComplete
2010-03-28 15:08:11 684 Page_PreRender
2010-03-28 15:08:11 684 Page_SaveStateComplete
2010-03-28 15:08:11 700 Page_Unload
2010-03-28 15:08:11 700 Application_PostRequestHandlerExecute
2010-03-28 15:08:11 700 Application_ReleaseRequestState
2010-03-28 15:08:11 700 Application_PostReleaseRequestState
2010-03-28 15:08:11 700 Application_UpdateRequestCache
2010-03-28 15:08:11 700 Application_PostUpdateRequestCache
2010-03-28 15:08:11 700 Application_EndRequest
2010-03-28 15:08:11 700 Application_PreSendRequestHeaders
2010-03-28 15:08:11 700 Application_PreSendRequestContent
2010-03-28 15:08:11 793 Application_BeginRequest
2010-03-28 15:08:11 793 Application_AuthenticateRequest
2010-03-28 15:08:11 793 Application_PostAuthenticateRequest
2010-03-28 15:08:11 793 Application_AuthorizeRequest
2010-03-28 15:08:11 793 Application_PostAuthorizeRequest
2010-03-28 15:08:11 793 Application_ResolveRequestCache
2010-03-28 15:08:11 793 Application_PostResolveRequestCache
2010-03-28 15:08:11 809 Application_PostMapRequestHandler
2010-03-28 15:08:11 809 Application_AcquireRequestState
2010-03-28 15:08:11 809 Application_PostAcquireRequestState
2010-03-28 15:08:11 809 Application_PreRequestHandlerExecute
2010-03-28 15:08:11 825 Application_PostRequestHandlerExecute
2010-03-28 15:08:11 825 Application_ReleaseRequestState
2010-03-28 15:08:11 840 Application_PostReleaseRequestState
2010-03-28 15:08:11 949 Application_UpdateRequestCache
2010-03-28 15:08:11 949 Application_PostUpdateRequestCache
2010-03-28 15:08:11 965 Application_EndRequest
2010-03-28 15:08:11 981 Application_PreSendRequestHeaders
2010-03-28 15:08:11 981 Application_PreSendRequestContent
哇！原来一个页面访问下来，会调用到这么多的方法，怪不得很多高并发的大型网站，通常都要自己写一个精减的HttpHandler用来取代Page做为基类，以期望获得更好的性能
最后：我们在做网站开发时，不可能只用到Page页，很多时候还会用到UserControl（用户自定义控件），先看下它的继承关系，比如我们创建了一个TestUserControl的用户控件
TestUserControl --> UserControl ---> TemplateControl --> Control，最终在Control类的定义下，可以看到：
这似乎表明用户控件中，应该有Page_Init,Page_Load,Page_Unload...等事件，通常我们只用到Init,Load事件，如果加入一个用户控件后，整个生命周期就更复杂了：
2010-06-12 15:35:28 042 Application_Start
2010-06-12 15:35:28 072 Init
2010-06-12 15:35:28 072 Application_BeginRequest
2010-06-12 15:35:28 082 Application_AuthenticateRequest
2010-06-12 15:35:28 082 Application_PostAuthenticateRequest
2010-06-12 15:35:28 092 Application_AuthorizeRequest
2010-06-12 15:35:28 102 Application_PostAuthorizeRequest
2010-06-12 15:35:28 102 Application_ResolveRequestCache
2010-06-12 15:35:28 112 Application_PostResolveRequestCache
2010-06-12 15:35:28 122 Application_PostMapRequestHandler
2010-06-12 15:35:28 142 Application_EndRequest
2010-06-12 15:35:28 142 Application_PreSendRequestHeaders
2010-06-12 15:35:28 142 Application_PreSendRequestContent
2010-06-12 15:35:28 152 Application_BeginRequest
2010-06-12 15:35:28 152 Application_AuthenticateRequest
2010-06-12 15:35:28 162 Application_PostAuthenticateRequest
2010-06-12 15:35:28 162 Application_AuthorizeRequest
2010-06-12 15:35:28 162 Application_PostAuthorizeRequest
2010-06-12 15:35:28 172 Application_ResolveRequestCache
2010-06-12 15:35:28 172 Application_PostResolveRequestCache
2010-06-12 15:35:28 172 Application_PostMapRequestHandler
2010-06-12 15:35:28 172 Session_Start
2010-06-12 15:35:28 172 Application_AcquireRequestState
2010-06-12 15:35:28 182 Application_PostAcquireRequestState
2010-06-12 15:35:28 182 Application_PreRequestHandlerExecute
2010-06-12 15:35:28 192 Page_PreInit
2010-06-12 15:35:28 192 TestUserControl.Page_Init
2010-06-12 15:35:28 202 Page_Init
2010-06-12 15:35:28 202 TestUserControl.TestProperty.Set
2010-06-12 15:35:28 202 Page_InitComplete
2010-06-12 15:35:28 202 Page_PreLoad
2010-06-12 15:35:28 202 Page_Load
2010-06-12 15:35:28 202 TestUserControl.Page_Load
2010-06-12 15:35:28 202 TestUserControl.ShowData()
2010-06-12 15:35:28 212 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 212 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 212 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 212 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 212 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 222 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 222 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 222 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 222 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 222 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 232 TestUserControl.Repeater1.ItemDataBound()
2010-06-12 15:35:28 232 Page_LoadComplete
2010-06-12 15:35:28 232 Page_PreRender
2010-06-12 15:35:28 232 TestUserControl.Page_PreRender
2010-06-12 15:35:28 242 Page_SaveStateComplete
2010-06-12 15:35:28 242 TestUserControl.Page_Unload
2010-06-12 15:35:28 252 Page_Unload
2010-06-12 15:35:28 252 Application_PostRequestHandlerExecute
2010-06-12 15:35:28 252 Application_ReleaseRequestState
2010-06-12 15:35:28 252 Application_PostReleaseRequestState
2010-06-12 15:35:28 262 Application_UpdateRequestCache
2010-06-12 15:35:28 262 Application_PostUpdateRequestCache
2010-06-12 15:35:28 262 Application_EndRequest
2010-06-12 15:35:28 272 Application_PreSendRequestHeaders
2010-06-12 15:35:28 272 Application_PreSendRequestContent
2010-06-12 15:35:28 282 Application_BeginRequest
2010-06-12 15:35:28 292 Application_AuthenticateRequest
2010-06-12 15:35:28 292 Application_PostAuthenticateRequest
2010-06-12 15:35:28 302 Application_AuthorizeRequest
2010-06-12 15:35:28 302 Application_PostAuthorizeRequest
2010-06-12 15:35:28 302 Application_ResolveRequestCache
2010-06-12 15:35:28 312 Application_PostResolveRequestCache
2010-06-12 15:35:28 312 Application_PostMapRequestHandler
2010-06-12 15:35:28 322 Application_AcquireRequestState
2010-06-12 15:35:28 322 Application_PostAcquireRequestState
2010-06-12 15:35:28 322 Application_PreRequestHandlerExecute
2010-06-12 15:35:28 332 Application_PostRequestHandlerExecute
2010-06-12 15:35:28 332 Application_ReleaseRequestState
2010-06-12 15:35:28 332 Application_PostReleaseRequestState
2010-06-12 15:35:28 342 Application_UpdateRequestCache
2010-06-12 15:35:28 342 Application_PostUpdateRequestCache
2010-06-12 15:35:28 342 Application_EndRequest
2010-06-12 15:35:28 342 Application_PreSendRequestHeaders
2010-06-12 15:35:28 342 Application_PreSendRequestContent
2010-06-12 15:36:40 034 Session_End
更准确的页面生命周期解释，请查阅下面的文档，这是msdn官方网站对于Asp.Net页面生命周期的权威解释，http://files.cnblogs.com/yjmyzz/Asp.Net-Page-Life.rar
文中测试所用的源代码: http://files.cnblogs.com/yjmyzz/aspx_life_test.rar (用vs2010 RC打开)。
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