Asp.net的应用程序对象和页面生存周期
IIS在接到一个新的http请求后，最终会调用asp.net_isapi.dll的ISAPI扩展(特指IIS6.0环境，iis7.0的应用程序池默认为集成方式，相对有所变化)，然后传递到httpRuntimePipe(http运行时管道)，Asp.Net这时才开始运行(即HttpRunTime是Asp.Net真正的入口)，HttpRunTime会为每个asp.net应用自动创建一个HttpApplication的实例，而该实例中又包含以下属性:
注1
Application-->相当于传统意义上asp时代的application对象，通常用于定义一个asp.net应用的全局变量
Context-->HttpContext(上下文)类的实例【Asp.Net新增的】
Modules-->影响当前应用程序的HttpModule模块集合
Request-->类似于asp中的Request对象，通常用于接收一些特定的值(比如Request.Form或Request.QueryString)
Response-->类似于asp中的Response对象，通常用于向做页面输出指定内容(比如Resonse.Write)
Server-->类似于asp中的Server对象，通过它能获得一些服务端的信息(比如Server.MapPath)
Session-->类似于asp中的Session对象
User-->用于获取用户认证相关的安全信息
从上面的属性可以发现：很多其实在asp年代已在使用，只有Context,Modules,User这三个是Asp.Net新增的
HttpApplication类除了具备"注1"的几个属性外，还有自己的方法，这里特别提一下Init方法和Dispose方法，这二个方法均可重载.
它们的调用时机为:
Init方法在Application_Start之后调用，而Dispose在Application_End之前调用，另外Application_Start在整个asp.net应用的生命周期内只激发一次(比如IIS启动或网站启动时)，类似的Application_End也只有当asp.net应用程序关闭时被调用(比如IIS停止或网站停止时)
除了Application_Start和Application_End方法，HttpApplication还提供了以下事件:
这些事件包括前面提到的可重载的Init及Dispose方法，再加上Session对应的Session_Start与Session_End方法，均可直接在Global.ascx.cs中以Application_XXX的形式使用(因为Global.ascx.cs中定义的类Global本身就是继承自HttpApplication的)
publicclassGlobal:System.Web.HttpApplication
再来看一下相对asp而言，新增的Context,Modules,User这三个属性
Context：
Context即HttpContext类的实例，在几乎整个aspx页面生命周期中，Context上下文一直伴随着各个环节向下传递
所以我们几乎可以在web应用中的任何环节，用HttpContext.Current来引用到当前的上下文实例，从HttpContext的定义上，还可以发现Context本身的属性中，又可以得到Application,ApplicationInstance,Profile,Response.Request...等对象的实例引用
回想一下：
publicclassHandler1:IHttpHandler
{
publicvoidProcessRequest(HttpContextcontext)
{
context.Response.ContentType="text/plain";
context.Response.Write("HelloWorld");
}
publicboolIsReusable
{
get
{
returnfalse;
}
}
}
我们在使用一个ashx文件时，ProcessRequest方法便是把当前上下文传递进来，进而通过context得到Response对象的引用，最终可以向页面输出任何想要的内容.
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:
注2
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WindowsNT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：
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： 2010-03-2815:01:39491Init 2010-03-2815:01:39491Application_BeginRequest 2010-03-2815:01:39506Application_AuthenticateRequest 2010-03-2815:01:39506Application_PostAuthenticateRequest 2010-03-2815:01:39506Application_AuthorizeRequest 2010-03-2815:01:39522Application_PostAuthorizeRequest 2010-03-2815:01:39522Application_ResolveRequestCache 2010-03-2815:01:39522Application_PostResolveRequestCache 2010-03-2815:01:39522Application_PostMapRequestHandler 2010-03-2815:01:39522Application_AcquireRequestState 2010-03-2815:01:39537Application_PostAcquireRequestState 2010-03-2815:01:39537Application_PreRequestHandlerExecute 2010-03-2815:01:39553Application_Error 2010-03-2815:01:39553Application_EndRequest 2010-03-2815:01:39569Application_PreSendRequestHeaders 2010-03-2815:01:39569Application_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: 2010-03-2815:03:47704Application_AuthenticateRequest 2010-03-2815:03:47766Application_PostAuthenticateRequest 2010-03-2815:03:47766Application_AuthorizeRequest 2010-03-2815:03:47766Application_PostAuthorizeRequest 2010-03-2815:03:47766Application_ResolveRequestCache 2010-03-2815:03:47783Application_PostResolveRequestCache 2010-03-2815:03:48667Application_PostMapRequestHandler 2010-03-2815:03:48667Application_AcquireRequestState 2010-03-2815:03:48683Application_PostAcquireRequestState 2010-03-2815:03:48698Application_PreRequestHandlerExecute 2010-03-2815:03:48745Page_PreInit 2010-03-2815:04:02903Page_Unload 2010-03-2815:04:02903Application_Error 2010-03-2815:04:02918Application_EndRequest 2010-03-2815:04:02996Application_PreSendRequestHeaders 2010-03-2815:04:02996Application_PreSendRequestContent 2010-03-2815:04:03371Application_Disposed 2010-03-2815:04:03371Dispose 2010-03-2815:04:03386Application_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webServer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: 2010-03-2815:08:11591Init 2010-03-2815:08:11591Application_BeginRequest 2010-03-2815:08:11591Application_AuthenticateRequest 2010-03-2815:08:11591Application_PostAuthenticateRequest 2010-03-2815:08:11606Application_AuthorizeRequest 2010-03-2815:08:11606Application_PostAuthorizeRequest 2010-03-2815:08:11606Application_ResolveRequestCache 2010-03-2815:08:11606Application_PostResolveRequestCache 2010-03-2815:08:11622Application_PostMapRequestHandler 2010-03-2815:08:11637Application_EndRequest 2010-03-2815:08:11637Application_PreSendRequestHeaders 2010-03-2815:08:11637Application_PreSendRequestContent 2010-03-2815:08:11637Application_BeginRequest 2010-03-2815:08:11637Application_AuthenticateRequest 2010-03-2815:08:11653Application_PostAuthenticateRequest 2010-03-2815:08:11653Application_AuthorizeRequest 2010-03-2815:08:11653Application_PostAuthorizeRequest 2010-03-2815:08:11653Application_ResolveRequestCache 2010-03-2815:08:11653Application_PostResolveRequestCache 2010-03-2815:08:11653Application_PostMapRequestHandler 2010-03-2815:08:11653Session_Start 2010-03-2815:08:11653Application_AcquireRequestState 2010-03-2815:08:11653Application_PostAcquireRequestState 2010-03-2815:08:11653Application_PreRequestHandlerExecute 2010-03-2815:08:11669Page_PreInit 2010-03-2815:08:11684Page_Init 2010-03-2815:08:11684Page_InitComplete 2010-03-2815:08:11684Page_PreLoad 2010-03-2815:08:11684Page_Load 2010-03-2815:08:11684Page_LoadComplete 2010-03-2815:08:11684Page_PreRender 2010-03-2815:08:11684Page_SaveStateComplete 2010-03-2815:08:11700Page_Unload 2010-03-2815:08:11700Application_PostRequestHandlerExecute 2010-03-2815:08:11700Application_ReleaseRequestState 2010-03-2815:08:11700Application_PostReleaseRequestState 2010-03-2815:08:11700Application_UpdateRequestCache 2010-03-2815:08:11700Application_PostUpdateRequestCache 2010-03-2815:08:11700Application_EndRequest 2010-03-2815:08:11700Application_PreSendRequestHeaders 2010-03-2815:08:11700Application_PreSendRequestContent 2010-03-2815:08:11793Application_BeginRequest 2010-03-2815:08:11793Application_AuthenticateRequest 2010-03-2815:08:11793Application_PostAuthenticateRequest 2010-03-2815:08:11793Application_AuthorizeRequest 2010-03-2815:08:11793Application_PostAuthorizeRequest 2010-03-2815:08:11793Application_ResolveRequestCache 2010-03-2815:08:11793Application_PostResolveRequestCache 2010-03-2815:08:11809Application_PostMapRequestHandler 2010-03-2815:08:11809Application_AcquireRequestState 2010-03-2815:08:11809Application_PostAcquireRequestState 2010-03-2815:08:11809Application_PreRequestHandlerExecute 2010-03-2815:08:11825Application_PostRequestHandlerExecute 2010-03-2815:08:11825Application_ReleaseRequestState 2010-03-2815:08:11840Application_PostReleaseRequestState 2010-03-2815:08:11949Application_UpdateRequestCache 2010-03-2815:08:11949Application_PostUpdateRequestCache 2010-03-2815:08:11965Application_EndRequest 2010-03-2815:08:11981Application_PreSendRequestHeaders 2010-03-2815:08:11981Application_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： 2010-06-1215:35:28042Application_Start 2010-06-1215:35:28072Init 2010-06-1215:35:28072Application_BeginRequest 2010-06-1215:35:28082Application_AuthenticateRequest 2010-06-1215:35:28082Application_PostAuthenticateRequest 2010-06-1215:35:28092Application_AuthorizeRequest 2010-06-1215:35:28102Application_PostAuthorizeRequest 2010-06-1215:35:28102Application_ResolveRequestCache 2010-06-1215:35:28112Application_PostResolveRequestCache 2010-06-1215:35:28122Application_PostMapRequestHandler 2010-06-1215:35:28142Application_EndRequest 2010-06-1215:35:28142Application_PreSendRequestHeaders 2010-06-1215:35:28142Application_PreSendRequestContent 2010-06-1215:35:28152Application_BeginRequest 2010-06-1215:35:28152Application_AuthenticateRequest 2010-06-1215:35:28162Application_PostAuthenticateRequest 2010-06-1215:35:28162Application_AuthorizeRequest 2010-06-1215:35:28162Application_PostAuthorizeRequest 2010-06-1215:35:28172Application_ResolveRequestCache 2010-06-1215:35:28172Application_PostResolveRequestCache 2010-06-1215:35:28172Application_PostMapRequestHandler 2010-06-1215:35:28172Session_Start 2010-06-1215:35:28172Application_AcquireRequestState 2010-06-1215:35:28182Application_PostAcquireRequestState 2010-06-1215:35:28182Application_PreRequestHandlerExecute 2010-06-1215:35:28192Page_PreInit 2010-06-1215:35:28192TestUserControl.Page_Init 2010-06-1215:35:28202Page_Init 2010-06-1215:35:28202TestUserControl.TestProperty.Set 2010-06-1215:35:28202Page_InitComplete 2010-06-1215:35:28202Page_PreLoad 2010-06-1215:35:28202Page_Load 2010-06-1215:35:28202TestUserControl.Page_Load 2010-06-1215:35:28202TestUserControl.ShowData() 2010-06-1215:35:28212TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28212TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28212TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28212TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28212TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28222TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28222TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28222TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28222TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28222TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28232TestUserControl.Repeater1.ItemDataBound() 2010-06-1215:35:28232Page_LoadComplete 2010-06-1215:35:28232Page_PreRender 2010-06-1215:35:28232TestUserControl.Page_PreRender 2010-06-1215:35:28242Page_SaveStateComplete 2010-06-1215:35:28242TestUserControl.Page_Unload 2010-06-1215:35:28252Page_Unload 2010-06-1215:35:28252Application_PostRequestHandlerExecute 2010-06-1215:35:28252Application_ReleaseRequestState 2010-06-1215:35:28252Application_PostReleaseRequestState 2010-06-1215:35:28262Application_UpdateRequestCache 2010-06-1215:35:28262Application_PostUpdateRequestCache 2010-06-1215:35:28262Application_EndRequest 2010-06-1215:35:28272Application_PreSendRequestHeaders 2010-06-1215:35:28272Application_PreSendRequestContent 2010-06-1215:35:28282Application_BeginRequest 2010-06-1215:35:28292Application_AuthenticateRequest 2010-06-1215:35:28292Application_PostAuthenticateRequest 2010-06-1215:35:28302Application_AuthorizeRequest 2010-06-1215:35:28302Application_PostAuthorizeRequest 2010-06-1215:35:28302Application_ResolveRequestCache 2010-06-1215:35:28312Application_PostResolveRequestCache 2010-06-1215:35:28312Application_PostMapRequestHandler 2010-06-1215:35:28322Application_AcquireRequestState 2010-06-1215:35:28322Application_PostAcquireRequestState 2010-06-1215:35:28322Application_PreRequestHandlerExecute 2010-06-1215:35:28332Application_PostRequestHandlerExecute 2010-06-1215:35:28332Application_ReleaseRequestState 2010-06-1215:35:28332Application_PostReleaseRequestState 2010-06-1215:35:28342Application_UpdateRequestCache 2010-06-1215:35:28342Application_PostUpdateRequestCache 2010-06-1215:35:28342Application_EndRequest 2010-06-1215:35:28342Application_PreSendRequestHeaders 2010-06-1215:35:28342Application_PreSendRequestContent 2010-06-1215:36:40034Session_End
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：
2010-03-2815:01:39413Application_Start
2010-03-2815:03:47704Application_BeginRequest
2010-03-2815:08:11513Application_Start
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