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HttpResponse的Output与OutputStream、Filter关系与区别介绍

时间:2019-10-09 14:53     来源/作者:asp.net教程网

在网上经常看见有这样的代码 

HttpResponse response = HttpContext.Current.Response; 
response.Filter = new PageFilter(response.Filter); 

来拦截输出流,自己也做个类似的东东,如asp.net中 js 合并 压缩,现在我也来说说这几个东东是什么吧,需要大家对asp.net的生命周期比较熟悉,如不熟悉的朋友建议先看看ASP.NET 请求处理流程 ASP.NET管线与应用程序生命周期 

首先我们来看看这3个属性的源代码吧: 

复制代码代码如下:


public TextWriter Output 

get 

return this._writer; 

set 

this._writer = value; 




public Stream OutputStream 

get 

if (!this.UsingHttpWriter) 

throw new HttpException(SR.GetString("OutputStream_NotAvail")); 

return this._httpWriter.OutputStream; 

 

复制代码代码如下:


public Stream Filter 

get 

if (this.UsingHttpWriter) 

return this._httpWriter.GetCurrentFilter(); 

return null; 

set 

if (!this.UsingHttpWriter) 

throw new HttpException(SR.GetString("Filtering_not_allowed")); 

this._httpWriter.InstallFilter(value); 
IIS7WorkerRequest request = this._wr as IIS7WorkerRequest; 
if (request != null) 

request.ResponseFilterInstalled(); 


}


我们看到Filter和OutputStream都用到了一个属性UsingHttpWriter,那这个属性是怎么定义的了

复制代码代码如下:


private bool UsingHttpWriter 

get 

return ((this._httpWriter != null) && (this._writer == this._httpWriter)); 

}


从这个属性我们可以知道_writer 、_httpWriter实际上是同一个东东,它们的类型是HttpWriter ,而HttpWriter 又继承与TextWriter。现在我们可以解释Output就是_httpWriter,而OutputStream是_httpWriter的OutputStream属性。类HttpWriter 主要代码如下

复制代码代码如下:


public Stream OutputStream 

get 

return this._stream; 




internal HttpWriter(HttpResponse response) : base(null) 

this._response = response; 
this._stream = new HttpResponseStream(this); 
this._buffers = new ArrayList(); 
this._lastBuffer = null; 
this._charBuffer = (char[]) s_Allocator.GetBuffer(); 
this._charBufferLength = this._charBuffer.Length; 
this._charBufferFree = this._charBufferLength; 
this.UpdateResponseBuffering(); 



internal HttpResponseStream(HttpWriter writer) 

this._writer = writer; 
}


HttpResponse 在Filter属性设置调用了HttpWriter类的InstallFilter方法,而获取调用了该类的GetCurrentFilter 

复制代码代码如下:


internal void InstallFilter(Stream filter) 

if (this._filterSink == null) 

throw new HttpException(SR.GetString("Invalid_response_filter")); 

this._installedFilter = filter; 


internal Stream GetCurrentFilter() 

if (this._installedFilter != null) 

return this._installedFilter; 

if (this._filterSink == null) 

this._filterSink = new HttpResponseStreamFilterSink(this); 

return this._filterSink; 
}


由以上代码我们可以得知HttpResponse的输出流就是Filter属性设置的流,即HttpResponse的Output和OutputStream属性的输出流都是来自Filter中的流。我们来看看_writer 、_httpWriter它们是在什么时候初始化的了?在HttpResonse中有一个方法

复制代码代码如下:


internal void InitResponseWriter() 

if (this._httpWriter == null) 

this._httpWriter = new HttpWriter(this); 
this._writer = this._httpWriter; 


该方法是由HttpRuntime的ProcessRequestInternal来调用

复制代码代码如下:


private void ProcessRequestInternal(HttpWorkerRequest wr) 

HttpContext context; 
try 

context = new HttpContext(wr, false); 

catch 

wr.SendStatus(400, "Bad Request"); 
wr.SendKnownResponseHeader(12, "text/html; charset=utf-8"); 
byte[] bytes = Encoding.ASCII.GetBytes("<html><body>Bad Request</body></html>"); 
wr.SendResponseFromMemory(bytes, bytes.Length); 
wr.FlushResponse(true); 
wr.EndOfRequest(); 
return; 

wr.SetEndOfSendNotification(this._asyncEndOfSendCallback, context); 
Interlocked.Increment(ref this._activeRequestCount); 
HostingEnvironment.IncrementBusyCount(); 
try 

try 

this.EnsureFirstRequestInit(context); 

catch 

if (!context.Request.IsDebuggingRequest) 

throw; 


context.Response.InitResponseWriter(); 
IHttpHandler applicationInstance = HttpApplicationFactory.GetApplicationInstance(context); 
if (applicationInstance == null) 

throw new HttpException(SR.GetString("Unable_create_app_object")); 

if (EtwTrace.IsTraceEnabled(5, 1)) 

EtwTrace.Trace(EtwTraceType.ETW_TYPE_START_HANDLER, context.WorkerRequest, applicationInstance.GetType().FullName, "Start"); 

if (applicationInstance is IHttpAsyncHandler) 

IHttpAsyncHandler handler2 = (IHttpAsyncHandler) applicationInstance; 
context.AsyncAppHandler = handler2; 
handler2.BeginProcessRequest(context, this._handlerCompletionCallback, context); 

else 

applicationInstance.ProcessRequest(context); 
this.FinishRequest(context.WorkerRequest, context, null); 


catch (Exception exception) 

context.Response.InitResponseWriter(); 
this.FinishRequest(wr, context, exception); 

}

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