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HttpResponse的Output與OutputStream、Filter關係與區別介紹

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在網上經常看見有這樣的代碼

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

來攔截輸出資料流，自己也做個類似的東東，如asp.net中 js 合并 壓縮，現在我也來說說這幾個東東是什麼吧，需要大家對asp.net的生命週期比較熟悉，如不熟悉的朋友建議先看看ASP.NET 請求處理流程 ASP.NET管線與應用程式生命週期

首先我們來看看這3個屬性的原始碼吧：

複製代碼 代碼如下: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;
}
}

複製代碼 代碼如下: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();
}
}
}

我們看到Filter和OutputStream都用到了一個屬性UsingHttpWriter，那這個屬性是怎麼定義的了複製代碼 代碼如下:private bool UsingHttpWriter
{
get
{
return ((this._httpWriter != null) && (this._writer == this._httpWriter));
}
}

從這個屬性我們可以知道_writer 、_httpWriter實際上是同一個東東，它們的類型是HttpWriter ，而HttpWriter 又繼承與TextWriter。現在我們可以解釋Output就是_httpWriter，而OutputStream是_httpWriter的OutputStream屬性。類HttpWriter 主要代碼如下複製代碼 代碼如下: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屬性設定調用了HttpWriter類的InstallFilter方法，而擷取調用了該類的GetCurrentFilter 複製代碼 代碼如下: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;
}

由以上代碼我們可以得知HttpResponse的輸出資料流就是Filter屬性設定的流,即HttpResponse的Output和OutputStream屬性的輸出資料流都是來自Filter中的流。我們來看看_writer 、_httpWriter它們是在什麼時候初始化的了？在HttpResonse中有一個方法複製代碼 代碼如下:internal void InitResponseWriter()
{
if (this._httpWriter == null)
{
this._httpWriter = new HttpWriter(this);
this._writer = this._httpWriter;
}
}

該方法是由HttpRuntime的ProcessRequestInternal來調用複製代碼 代碼如下: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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