https://www.cnblogs.com/JimmyZhang/archive/2007/09/04/880967.html
IHttpModule
HTTPRuntime（運行時）。在一個控制台程序中，程序的入口是Program中的Main方法。那么，一個網站的入口在哪里呢？在最開始的ashx中，有個ProcessRequest方法，后來在WebForm中，在后台是一個不分類，繼承自Page類，在Page_Load方法中去寫代碼。其實Page類型也有一個ProcessRequest的虛方法。
都是這個ProcessRequest方法來處理請求的。在MVC中也是如此。在MVC中，任何一個Http請求，一定有一個IHttpHandler來處理，在這個接口中，定義了一個ProcessRequest方法。HttpApplication繼承自IHttpHandler接口。任何一個Http請求就是一個HttpApplication對象來處理的，然后處理過程固定包含權限認證、緩存處理、Session處理、Cookie出庫、生成html、輸出客戶端，與此同時，千千萬萬的開發者，又有各種各樣的擴展訴求，任何一個環節都有可能擴展，如果是我們來設計，該怎么設計？
其實在MVC框架里面，用到的是觀察者模式：
在HttpApplication類型，有這些事件：
// // 摘要: // Occurs just before ASP.NET sends HTTP headers to the client. public event EventHandler PreSendRequestHeaders; // // 摘要: // Occurs when the handler is selected to respond to the request. public event EventHandler MapRequestHandler; // // 摘要: // Occurs when the application is disposed. public event EventHandler Disposed; // // 摘要: // Occurs as the first event in the HTTP pipeline chain of execution when ASP.NET // responds to a request. public event EventHandler BeginRequest; // // 摘要: // Occurs when a security module has established the identity of the user. public event EventHandler AuthenticateRequest; // // 摘要: // Occurs when a security module has established the identity of the user. public event EventHandler PostAuthenticateRequest; // // 摘要: // Occurs when a security module has verified user authorization. public event EventHandler AuthorizeRequest; // // 摘要: // Occurs when the user for the current request has been authorized. public event EventHandler PostAuthorizeRequest; // // 摘要: // Occurs when ASP.NET finishes an authorization event to let the caching modules // serve requests from the cache, bypassing execution of the event handler (for // example, a page or an XML Web service). public event EventHandler ResolveRequestCache; // // 摘要: // Occurs when ASP.NET bypasses execution of the current event handler and allows // a caching module to serve a request from the cache. public event EventHandler PostResolveRequestCache; // // 摘要: // Occurs just before ASP.NET sends content to the client. public event EventHandler PreSendRequestContent; // // 摘要: // Occurs when ASP.NET has mapped the current request to the appropriate event handler. public event EventHandler PostMapRequestHandler; // // 摘要: // Occurs when ASP.NET has completed processing all the event handlers for the System.Web.HttpApplication.LogRequest // event. public event EventHandler PostLogRequest; // // 摘要: // Occurs when the managed objects that are associated with the request have been // released. public event EventHandler RequestCompleted; // // 摘要: // Occurs when the request state (for example, session state) that is associated // with the current request has been obtained. public event EventHandler PostAcquireRequestState; // // 摘要: // Occurs just before ASP.NET starts executing an event handler (for example, a // page or an XML Web service). public event EventHandler PreRequestHandlerExecute; // // 摘要: // Occurs when the ASP.NET event handler (for example, a page or an XML Web service) // finishes execution. public event EventHandler PostRequestHandlerExecute; // // 摘要: // Occurs after ASP.NET finishes executing all request event handlers. This event // causes state modules to save the current state data. public event EventHandler ReleaseRequestState; // // 摘要: // Occurs when ASP.NET has completed executing all request event handlers and the // request state data has been stored. public event EventHandler PostReleaseRequestState; // // 摘要: // Occurs when ASP.NET finishes executing an event handler in order to let caching // modules store responses that will be used to serve subsequent requests from the // cache. public event EventHandler UpdateRequestCache; // // 摘要: // Occurs when ASP.NET finishes updating caching modules and storing responses that // are used to serve subsequent requests from the cache. public event EventHandler PostUpdateRequestCache; // // 摘要: // Occurs just before ASP.NET performs any logging for the current request. public event EventHandler LogRequest; // // 摘要: // Occurs when ASP.NET acquires the current state (for example, session state) that // is associated with the current request. public event EventHandler AcquireRequestState; // // 摘要: // Occurs as the last event in the HTTP pipeline chain of execution when ASP.NET // responds to a request. public event EventHandler EndRequest; // // 摘要: // Occurs when an unhandled exception is thrown. public event EventHandler Error;
這里用的是觀察者模式，把固定的步驟直接寫在handler里面，在步驟前后分別放一個事件，然后開發者可以對事件注冊動作，等着請求進來了，然后就可以按照順訊執行一下。這種設計是不是很完美？但是仍有不完美的地方，就是每個請求都要執行這些事件，太多管閑事了。在.NET Core中出現了中間件，比這種更加完美。后續再詳細介紹。
請見下列代碼
public class HttpProcessDemo { public class HttpApplicationDemo : IHttpHandler { public bool IsReusable => true; public event Action BeginRequest; public event Action EndRequest; public event Action PreSomething1Handler; public event Action PostSomething1Handler; public event Action PreSomething2Handler; public event Action PostSomething2Handler; public event Action PreSomething3Handler; public event Action PostSomething3Handler; public event Action PreSomething4Handler; public event Action PostSomething4Handler; public event Action PreSomething5Handler; public event Action PostSomething5Handler; public event Action PreSomething6Handler; public event Action PostSomething6Handler; public void ProcessRequest(HttpContext context) { this.BeginRequest?.Invoke(); this.PreSomething1Handler?.Invoke(); Console.WriteLine("Something 1"); this.PostSomething1Handler?.Invoke(); this.PreSomething2Handler?.Invoke(); Console.WriteLine("Something 2"); this.PostSomething2Handler?.Invoke(); this.PreSomething3Handler?.Invoke(); Console.WriteLine("Something 3"); this.PostSomething3Handler?.Invoke(); this.PreSomething4Handler?.Invoke(); Console.WriteLine("Something 4"); this.PostSomething4Handler?.Invoke(); this.PreSomething5Handler?.Invoke(); Console.WriteLine("Something 5"); this.PostSomething5Handler?.Invoke(); this.PreSomething6Handler?.Invoke(); Console.WriteLine("Something 6"); this.PostSomething6Handler?.Invoke(); this.EndRequest?.Invoke(); } //任何請求進來，只能是 123456 //事件升級后，可以在程序啟動時，實例化HttpApplicationDemo后，可以給事件注冊動作，請求再進來時，處理不僅是123456了，還有多個事件里面的動作 }
對HttpApplication里面的事件進行動作注冊，就叫IHttpModule。
自定義一個HttpModule+配置文件注冊，然后任何一個請求都會執行Init里面注冊給Application事件的動作。
public class CustomHttpModule : IHttpModule { public void Dispose() { Console.WriteLine(); } public event EventHandler CustomHttpModuleHandler; /// <summary> /// 注冊動作 /// </summary> /// <param name="context"></param> public void Init(HttpApplication application) { application.BeginRequest += (s, e) => { this.CustomHttpModuleHandler?.Invoke(application, null); }; //application.EndRequest += (s, e) => //{ // HttpContext.Current.Response.Write("CustomHttpModule.EndRequest"); //}; #region 為每一個事件，都注冊了一個動作，向客戶端輸出信息 application.AcquireRequestState += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "AcquireRequestState ")); application.AuthenticateRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "AuthenticateRequest ")); application.AuthorizeRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "AuthorizeRequest ")); application.BeginRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "BeginRequest ")); application.Disposed += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "Disposed ")); application.EndRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "EndRequest ")); application.Error += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "Error ")); application.LogRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "LogRequest ")); application.MapRequestHandler += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "MapRequestHandler ")); application.PostAcquireRequestState += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostAcquireRequestState ")); application.PostAuthenticateRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostAuthenticateRequest ")); application.PostAuthorizeRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostAuthorizeRequest ")); application.PostLogRequest += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostLogRequest ")); application.PostMapRequestHandler += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostMapRequestHandler ")); application.PostReleaseRequestState += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostReleaseRequestState ")); application.PostRequestHandlerExecute += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostRequestHandlerExecute ")); application.PostResolveRequestCache += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostResolveRequestCache ")); application.PostUpdateRequestCache += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PostUpdateRequestCache ")); application.PreRequestHandlerExecute += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PreRequestHandlerExecute ")); application.PreSendRequestContent += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PreSendRequestContent ")); application.PreSendRequestHeaders += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "PreSendRequestHeaders ")); application.ReleaseRequestState += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "ReleaseRequestState ")); application.RequestCompleted += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "RequestCompleted ")); application.ResolveRequestCache += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "ResolveRequestCache ")); application.UpdateRequestCache += (s, e) => application.Response.Write(string.Format("<h1 style='color:#00f'>來自MyCustomModule 的處理，{0}請求到達 {1}</h1><hr>", DateTime.Now.ToString(), "UpdateRequestCache ")); #endregion } }
訪問下頁面，就是這樣的結果：
正常流程下，會按照順序執行19個事件。
學完HttpModule，我們可以做點什么有用的擴展？
任何一個請求都會執行HttpModuleInit里面注冊給Application的事件
1、日志-性能監控
2、權限
3、緩存
4、頁面加點東西
5、請求過濾
6、MVC就是一個Module的擴展
不適合的：不是針對全部請求的，就不太適合用Module，因為有性能損耗
1、多語言，根據Cookie信息去查詢不同的數據做不同的展示，如果是全部一套處理，最后HttpModule攔截+處理，適合httpModule
2、跳轉到不同界面，也不合適
3、防盜鏈，針對一類的后綴來處理的，而不是全部請求---判斷----再防盜鏈
在HttpModule里面發布一個CustomHttpModuleHandler，在Global增加一個動作CustomHttpModuleBingle_CustomHttpModuleHandler（配置文件module名稱_module里面事件名稱），請求響應時，該事件會執行
protected void CustomHttpModuleBingle_CustomHttpModuleHandler(object sender, EventArgs e) { this.logger.Info("this is CustomHttpModuleBingle_CustomHttpModuleHandler");
}
HttpModule是對HttpApplication的事件動作注冊動作，Global是對HttpModule里面的事件注冊動作。