深入了解asp.net裡的IHttpHandler
忍不住了,繼續貼。
1 、概述
說 明:HttpHandler是一個HTTP請求的真正進行中心。在HttpHandler容器中,ASP.NET Framework才調用HttpHandler的ProcessRequest成員方法來對這個HTTP請求進行真正的處理,真正地對用戶端請求的服務 器頁面做出編譯和執行,并将處理過後的資訊附加在HTTP請求資訊流中再次傳回到HttpModule中。
2、舉例
以一個aspx頁面為 例,正是在HttpHandler這裡,一個aspx頁面才被系統處了解析,并将處理完成的結果繼續經由HttpModule傳遞下去,直至到達用戶端。 當然,對于aspx頁面,ASP.NET Framework在預設情況下是交給System.Web.UI.PageHandlerFactory這個HttpHandlerFactory 來處理的。當一個HTTP請求到達這個HttpHandlerFactory時,HttpHandlerFactory會提供出一個HttpHandler容器,交由這個HttpHandler容器來處理這個HTTP請求。 一個HTTP請求都是最終交給一個HttpHandler容器中的ProcessRequest方法來處理的。
3、HttpHandler
(1)實作HttpHandler,必須繼承自IHttpHandler接口。下面是這個接口的定義:
Code
using System;
namespace System.Web
{
// Summary:
// Defines the contract that ASP.NET implements to synchronously process HTTP
// Web requests using custom HTTP handlers.
public interface IHttpHandler
{
// Summary:
// Gets a value indicating whether another request can use the System.Web.IHttpHandler
// instance.
//
// Returns:
// true if the System.Web.IHttpHandler instance is reusable; otherwise, false.
// 其他Request是否可以使用IHttpHandler
bool IsReusable { get ; }
// Summary:
// Enables processing of HTTP Web requests by a custom HttpHandler that implements
// the System.Web.IHttpHandler interface.
//
// Parameters:
// context:
// An System.Web.HttpContext object that provides references to the intrinsic
// server objects (for example, Request, Response, Session, and Server) used
// to service HTTP requests.
// 處理HttpRequest
void ProcessRequest(HttpContext context);
}
}
(2)自定義HttpHandler
a、代碼
建立一個網站,default.aspx頁面:
default.aspx.cs:
Code
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load( object sender, EventArgs e)
{
Response.Write( " <br/>來自Default.aspx頁面<br/> " );
}
}
新添一個類庫MyHandler,添加一個類如下:
Code
using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
using System.Web.SessionState;
namespace MyHandler
{
/// <summary>
/// 如果要在HttpHandler容器中使用Session,必須要實作IRequiresSessionState接口
/// </summary>
public class MyTestHandler : IHttpHandler, IRequiresSessionState
{
public bool IsReusable
{
get { return true ; }
}
public void ProcessRequest(HttpContext context)
{
context.Response.Write( " <h3><b>This is a HttpHandler Test</b></h3> " );
context.Session[ " Test " ] = " <h3><span style=/ " color:blue;/ " >在HttpHandler容器中調用Session</span></h3> " ;
context.Response.Write(context.Session[ " Test " ]);
}
}
}
要在HttpHandler使用Session,我在舊文aspx,ascx和ashx使用小結 裡已經提及。
b、配置檔案
在web.config檔案的system.web節點下,添加:
<httpHandlers>
<add verb="*" path="*" type="MyHandler.MyTestHandler, MyHandler"/>
</httpHandlers>
c、注意
<1>、.NET為asp.net提供了很多系統預設HttpHandler類,用來适應不同類型的HttpRequest。比如aspx,在machine.config中是這樣定義的:
<add verb="*" path="*.aspx" type="System.Web.UI.PageHandlerFactory"/>
這就說明遇到aspx的Request請求,asp.net會将其交給System.Web.UI.PageHandlerFactory的HttpHandler類來處理。
<2>、如果自己定義了新的HttpHandler,而且在web.config中指定,則系統隻會使用這個新的HttpHandler,而不再使用原先預設的或者指定的.
<3>、直接拷貝類庫的bin目錄下的檔案到網站bin下.
4、HttpHandlerFactory
ASP.NET Framework實際不直接将相關的頁面資源HTTP請求定位到一個其内部預設的IHttpHandler容器之上,而定位到了其内部預設的 IHttpHandler工廠上。IHttpHandler工廠的作用是對IHttpHandler容器進行排程和管理,這樣做的優點是大大增強了系統的 負荷性,提升了效率。
(1)IHttpHandlerFactory接口
IHttpHandlerFactory接口包含兩個方法:GetHandler方法傳回實作IHttpHandler接口的類的執行個體,ReleaseHandler方法使工廠可以重用現有的處理程式執行個體。
Code
using System;
using System.Web;
namespace System.Web.UI
{
// Summary:
// Creates instances of classes that inherit from the System.Web.UI.Page class
// and implement the System.Web.IHttpHandler interface. Instances are created
// dynamically to handle requests for ASP.NET files. The System.Web.UI.PageHandlerFactory
// class is the default handler factory implementation for ASP.NET pages.
public class PageHandlerFactory : System.Web.IHttpHandlerFactory2, IHttpHandlerFactory
{
// Summary:
// Initializes a new instance of the System.Web.UI.PageHandlerFactory class.
protected internal PageHandlerFactory();
// Summary:
// Returns an instance of the System.Web.IHttpHandler interface to process the
// requested resource.
//
// Parameters:
// context:
// An instance of the System.Web.HttpContext class that provides references
// to intrinsic server objects (for example, Request, Response, Session, and
// Server) used to service HTTP requests.
//
// requestType:
// The HTTP data transfer method (GET or POST) that the client uses.
//
// virtualPath:
// The virtual path to the requested resource.
//
// path:
// The System.Web.HttpRequest.PhysicalApplicationPath property to the requested
// resource.
//
// Returns:
// A new System.Web.IHttpHandler that processes the request; otherwise, null.
public virtual IHttpHandler GetHandler(HttpContext context, string requestType, string virtualPath, string path);
//
// Summary:
// Enables a factory to reuse an existing instance of a handler.
//
// Parameters:
// handler:
// The System.Web.IHttpHandler to reuse.
public virtual void ReleaseHandler(IHttpHandler handler);
}
}
(2) 實作一個簡單的HttpHandler工廠
類庫新添一個檔案MyHandlerFactor.cs:
Code
using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
namespace MyHandler
{
public class MyHandlerFactory : IHttpHandlerFactory
{
public IHttpHandler GetHandler(HttpContext context, string requestType, string url, string pathTranslated)
{
string fileName = url.Substring(url.LastIndexOf( ' / ' ) + 1 );
string objName = fileName.Substring( 0 , fileName.IndexOf( ' . ' ));
string className = " MyHandler. " + objName;
object objHandler = null ;
try
{
// 采用動态反射機制建立相應的IHttpHandler實作類。
objHandler = Activator.CreateInstance(Type.GetType(className));
context.Response.Write(className);
// context.Response.Redirect("default.aspx");
}
catch (Exception e)
{
throw new HttpException( " 工廠不能為類型 " + objName + " 建立執行個體。 " , e);
}
return (IHttpHandler)objHandler;
}
public void ReleaseHandler(IHttpHandler handler)
{
}
}
public class Handler1 : IHttpHandler
{
public bool IsReusable
{
get { return true ; }
}
public void ProcessRequest(HttpContext context)
{
context.Response.Write( " <br/>這是來自于MyHandlerFactory裡的處理.<br/> " );
context.Response.Write( " <h3>來自Handler1的資訊.</h3> " );
}
}
public class Handler2 : IHttpHandler
{
public bool IsReusable
{
get { return true ; }
}
public void ProcessRequest(HttpContext context)
{
context.Response.Write( " <br/>這是來自于MyHandlerFactory裡的處理.<br/> " );
context.Response.Write( " <h3>來自Handler2的資訊.</h3> " );
}
}
}
網站新添兩個檔案,Handler1.aspx和Handler2.aspx。它們的cs檔案:
Code
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class Handler1 : System.Web.UI.Page
{
protected void Page_Load( object sender, EventArgs e)
{
Response.Write( " 這是來自于MyHandler頁面直接輸出... " ); // 這一句不起作用了,MyHandlerFactory已經對該頁面的HttpContext進行了處理
}
}
接着重新修改配置檔案:
<httpHandlers>
<add verb="*" path="Handler1.aspx" type="MyHandler.MyHandlerFactory, MyHandler"/>
<add verb="*" path="Handler2.aspx" type="MyHandler.MyHandlerFactory, MyHandler"/>
</httpHandlers>
到這裡,針對Handler1.aspx和Handler2.aspx兩個頁面的http請求我們就通過HttpHandler工廠處理好了。
5、HttpHandler和HttpModule的差別
主要有兩點:
(1)先後次序.先IHttpModule,後IHttpHandler,IHttpHandler處理結束後再交給IHttpModule;
(2)對請求的處理上:
IHttpModule是屬于大小通吃類型,無論用戶端請求的是什麼檔案,都會調用到它;例如aspx,html,rar的請求;
IHttpHandler則屬于挑食類型,隻有asp.net注冊過的檔案類型(例如aspx,ascx,asmx等等)才會輪到調用它。