HttpHandler

转自http://ugoer.cnblogs.com/archive/2005/09/07/231676.html

HttpHandler实现了ISAPI Extention的功能，他处理请求(Request)的信息和发送响应(Response)。HttpHandler功能的实现通过实现IHttpHandler接口来达到。

看图先：

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在ASP.NET 管道处理的末端是HTTP Hander，其实每个Asp.net的Page都实现了IHttpHander，在VS.net中的对象察看器中你可以证实这一点

具体的类是这样定义的：public class Page : TemplateControl, IhttpHandler。

接口IHttpHandler的定义如下：

interface IHttpHandler

{

voidProcessRequest(HttpContextctx);

boolIsReuseable{get;}

}

接口中

ProcessRequest 是添加自己的代码进行相应处理的地方。 IsReuseable 属性指明该 HttpHandler 的实现类是否需要缓存。

在CS中有很多继承IHttpHandler接口的类，我取出有代表性而又容易理解的一个做分析：找到CommunityServerComponents项目Components目录下的Redirect.cs文件，内容如下：

// ------------------------------------------------------------------------------
// <copyrightcompany="TelligentSystems">
// Copyright(c)TelligentSystemsCorporation.Allrightsreserved.
// </copyright>
// ------------------------------------------------------------------------------

using System;
using System.Web;

namespace CommunityServer.Components
{
/**////<summary>
///SummarydescriptionforRedirect.
///</summary>
publicclassRedirect:IHttpHandler
{
publicRedirect()
{
//
//TODO:Addconstructorlogichere
//
}

publicvoidProcessRequest(HttpContextcontext)
{
stringurl=context.Request.QueryString["u"];
if(!Globals.IsNullorEmpty(url))
{
context.Response.Redirect(url);

}
else
{
context.Response.Redirect(Globals.GetSiteUrls().Home);
}

context.Response.End();
}

publicboolIsReusable
{
get{returnfalse;}
}
}
}

这里的Redirect功能是在web请求满足HttpHandler配置文件中预设条件下自动拦截执行的，在web.config中<httpHandlers>节点下可以看到

< add verb ="GET" path ="Utility/redirect.aspx" type ="CommunityServer.Components.Redirect,CommunityServer.Components" />

对该类的配置

· verb可以是"GET"或"POST"，表示对GET或POST的请求进行处理。"*"表示对所有请求进行处理，这里是对GET请求进行处理。

· path指明对相应的文件进行处理，"*.aspx"表示对发给所有ASPX页面的请求进行处理，这里单独对redirect.aspx页面进行处理。可以指明路径，如"blogs"。表明只对blogs目录下的redirect.aspx文件请求进行处理。

· type属性中，逗号前的字符串指明HttpHandler的实现类的类名，后面的字符串指明Dll文件的名称。

实际处理是怎么样的呢？其实redirect.aspx页面在CS项目中并不存在，CS把对redirect.aspx的请求处理交给了CommunityServer.Components.dll程序集中Redirect类进行处理。处理的过程是执行

public void ProcessRequest(HttpContext context)

方法(Redirect类下的ProcessRequest方法是对当前请求的上下文Context中Url是否包含“u”参数，如果有并且参数值不为null就调用Response.Redirect方法跳转到“u”参数值所执行的页面，如果没有参数或者参数值为空就跳转到CS的首页)。

另外在CS中对RSS和Trackback的处理都使用了httpHandler的处理方式。

前面提到，所有页面的基类Page都实现了HttpHandler接口，因此每个asp.net的页面都可以看成是一个HttpHandler处理类，只是配置部分在machine.config中

< httpHandlers >
< add verb ="*" path ="*.vjsproj" type ="System.Web.HttpForbiddenHandler" />< add verb ="*" path ="*.java" type ="System.Web.HttpForbiddenHandler" />< add verb ="*" path ="*.jsl" type ="System.Web.HttpForbiddenHandler" />< add verb ="*" path ="trace.axd" type ="System.Web.Handlers.TraceHandler" />
< add verb ="*" path ="*.aspx" type ="System.Web.UI.PageHandlerFactory" />
< add verb ="*" path ="*.ashx" type ="System.Web.UI.SimpleHandlerFactory" />
< add verb ="*" path ="*.asmx" type ="System.Web.Services.Protocols.WebServiceHandlerFactory,System.Web.Services,Version=1.0.5000.0,Culture=neutral,PublicKeyToken=b03f5f7f11d50a3a" validate ="false" />
< add verb ="*" path ="*.rem" type ="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory,System.Runtime.Remoting,Version=1.0.5000.0,Culture=neutral,PublicKeyToken=b77a5c561934e089" validate ="false" />
< add verb ="*" path ="*.soap" type ="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory,System.Runtime.Remoting,Version=1.0.5000.0,Culture=neutral,PublicKeyToken=b77a5c561934e089" validate ="false" />
< add verb ="*" path ="*.asax" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.ascx" type ="System.Web.HttpForbiddenHandler" />
< add verb ="GET,HEAD" path ="*.dll.config" type ="System.Web.StaticFileHandler" />
< add verb ="GET,HEAD" path ="*.exe.config" type ="System.Web.StaticFileHandler" />
< add verb ="*" path ="*.config" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.cs" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.csproj" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.vb" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.vbproj" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.webinfo" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.asp" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.licx" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.resx" type ="System.Web.HttpForbiddenHandler" />
< add verb ="*" path ="*.resources" type ="System.Web.HttpForbiddenHandler" />
< add verb ="GET,HEAD" path ="*" type ="System.Web.StaticFileHandler" />
< add verb ="*" path ="*" type ="System.Web.HttpMethodNotAllowedHandler" />
</ httpHandlers >

借助一个工具：Reflector，看看Page类下的HttpHandler处理方法ProcessRequest都做了什么

[EditorBrowsable(EditorBrowsableState.Never)]
public void ProcessRequest(HttpContextcontext)
{
this.SetIntrinsics(context);
this.ProcessRequest();
}
private void SetIntrinsics(HttpContextcontext)
{
this._context=context;
this._request=context.Request;
this._response=context.Response;
this._application=context.Application;
this._cache=context.Cache;
if((this._clientTarget!=null)&&(this._clientTarget.Length>0))
{
this._request.ClientTarget=this._clientTarget;
}
base.HookUpAutomaticHandlers();
}
private void ProcessRequest()
{
Threadthread1=Thread.CurrentThread;
CultureInfoinfo1=thread1.CurrentCulture;
CultureInfoinfo2=thread1.CurrentUICulture;
this.FrameworkInitialize();
try
{
try
{
if(this.IsTransacted)
{
this.ProcessRequestTransacted();
}
else
{
this.ProcessRequestMain();
}
this.ProcessRequestEndTrace();
}
finally
{
this.ProcessRequestCleanup();
InternalSecurityPermissions.ControlThread.Assert();
thread1.CurrentCulture=info1;
thread1.CurrentUICulture=info2;
}
}
catch
{
throw;
}
}

在Page类的ProcessRequest方法先是把上下文Context内容赋值到当前Page中的一些属性里，然后调用System.Web.UI.TemplateControl中的HookUpAutomaticHandlers()

internal void HookUpAutomaticHandlers()
{
if(this.SupportAutoEvents)
{
SimpleBitVector32vector1=newSimpleBitVector32(this.AutoHandlers);
InternalSecurityPermissions.Reflection.Assert();
if(!vector1[1])
{
vector1[1]=true;
this.GetDelegateInformation("Page_Init",refvector1,2,4);
this.GetDelegateInformation("Page_Load",refvector1,8,0x10);
this.GetDelegateInformation("Page_DataBind",refvector1,0x20,0x40);
this.GetDelegateInformation("Page_PreRender",refvector1,0x80,0x100);
this.GetDelegateInformation("Page_Unload",refvector1,0x200,0x400);
this.GetDelegateInformation("Page_Error",refvector1,0x800,0x1000);
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