HttpWebRequest.KeepAlive Vlastnost
Definice
Důležité
Některé informace platí pro předběžně vydaný produkt, který se může zásadně změnit, než ho výrobce nebo autor vydá. Microsoft neposkytuje žádné záruky, výslovné ani předpokládané, týkající se zde uváděných informací.
Získá nebo nastaví hodnotu, která určuje, zda se má vytvořit trvalé připojení k internetovému prostředku.
public:
property bool KeepAlive { bool get(); void set(bool value); };
public bool KeepAlive { get; set; }
member this.KeepAlive : bool with get, set
Public Property KeepAlive As Boolean
Hodnota vlastnosti
true
, pokud by požadavek na internetový prostředek měl obsahovat hlavičku HTTP Connection
s hodnotou Keep-alive; jinak false
. Výchozí hodnota je true
.
Příklady
Následující příklad kódu nastaví KeepAlive vlastnost false
, aby se zabránilo navazování trvalého připojení k internetovému prostředku.
int main()
{
try
{
// Create a new HttpWebRequest object. Make sure that
// a default proxy is set if you are behind a firewall.
HttpWebRequest^ myHttpWebRequest1 = dynamic_cast<HttpWebRequest^>(WebRequest::Create( "http://www.contoso.com" ));
myHttpWebRequest1->KeepAlive = false;
// Assign the response object of HttpWebRequest to a HttpWebResponse variable.
HttpWebResponse^ myHttpWebResponse1 = dynamic_cast<HttpWebResponse^>(myHttpWebRequest1->GetResponse());
Console::WriteLine( "\nThe HTTP request Headers for the first request are: \n {0}", myHttpWebRequest1->Headers );
Console::WriteLine( "Press Enter Key to Continue.........." );
Console::Read();
Stream^ streamResponse = myHttpWebResponse1->GetResponseStream();
StreamReader^ streamRead = gcnew StreamReader( streamResponse );
array<Char>^readBuff = gcnew array<Char>(256);
int count = streamRead->Read( readBuff, 0, 256 );
Console::WriteLine( "The contents of the Html page are.......\n" );
while ( count > 0 )
{
String^ outputData = gcnew String( readBuff,0,count );
Console::Write( outputData );
count = streamRead->Read( readBuff, 0, 256 );
}
Console::WriteLine();
// Close the Stream object.
streamResponse->Close();
streamRead->Close();
// Release the resources held by response object.
myHttpWebResponse1->Close();
// Create a new HttpWebRequest object for the specified Uri.
HttpWebRequest^ myHttpWebRequest2 = dynamic_cast<HttpWebRequest^>(WebRequest::Create( "http://www.contoso.com" ));
myHttpWebRequest2->Connection = "Close";
// Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
HttpWebResponse^ myHttpWebResponse2 = dynamic_cast<HttpWebResponse^>(myHttpWebRequest2->GetResponse());
// Release the resources held by response object.
myHttpWebResponse2->Close();
Console::WriteLine( "\nThe Http RequestHeaders are \n {0}", myHttpWebRequest2->Headers );
Console::WriteLine( "\nPress 'Enter' Key to Continue........." );
Console::Read();
}
catch ( ArgumentException^ e )
{
Console::WriteLine( "\nThe second HttpWebRequest Object* has raised an Argument Exception as 'Connection' Property is set to 'Close'" );
Console::WriteLine( "\n {0}", e->Message );
}
catch ( WebException^ e )
{
Console::WriteLine( "WebException raised!" );
Console::WriteLine( "\n {0}", e->Message );
Console::WriteLine( "\n {0}", e->Status );
}
catch ( Exception^ e )
{
Console::WriteLine( "Exception raised!" );
Console::WriteLine( "Source : {0} ", e->Source );
Console::WriteLine( "Message : {0} ", e->Message );
}
}
class HttpWebRequest_Connection
{
static void Main()
{
try
{
// Create a new HttpWebRequest object.Make sure that
// a default proxy is set if you are behind a firewall.
HttpWebRequest myHttpWebRequest1 =
(HttpWebRequest)WebRequest.Create("http://www.contoso.com");
myHttpWebRequest1.KeepAlive=false;
// Assign the response object of HttpWebRequest to a HttpWebResponse variable.
HttpWebResponse myHttpWebResponse1 =
(HttpWebResponse)myHttpWebRequest1.GetResponse();
Console.WriteLine("\nThe HTTP request Headers for the first request are: \n{0}",myHttpWebRequest1.Headers);
Console.WriteLine("Press Enter Key to Continue..........");
Console.Read();
Stream streamResponse=myHttpWebResponse1.GetResponseStream();
StreamReader streamRead = new StreamReader( streamResponse );
Char[] readBuff = new Char[256];
int count = streamRead.Read( readBuff, 0, 256 );
Console.WriteLine("The contents of the Html page are.......\n");
while (count > 0)
{
String outputData = new String(readBuff, 0, count);
Console.Write(outputData);
count = streamRead.Read(readBuff, 0, 256);
}
Console.WriteLine();
// Close the Stream object.
streamResponse.Close();
streamRead.Close();
// Release the resources held by response object.
myHttpWebResponse1.Close();
// Create a new HttpWebRequest object for the specified Uri.
HttpWebRequest myHttpWebRequest2 =
(HttpWebRequest)WebRequest.Create("http://www.contoso.com");
myHttpWebRequest2.Connection="Close";
// Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
HttpWebResponse myHttpWebResponse2 =
(HttpWebResponse)myHttpWebRequest2.GetResponse();
// Release the resources held by response object.
myHttpWebResponse2.Close();
Console.WriteLine("\nThe Http RequestHeaders are \n{0}",myHttpWebRequest2.Headers);
Console.WriteLine("\nPress 'Enter' Key to Continue.........");
Console.Read();
}
catch(ArgumentException e)
{
Console.WriteLine("\nThe second HttpWebRequest object has raised an Argument Exception as 'Connection' Property is set to 'Close'");
Console.WriteLine("\n{0}",e.Message);
}
catch(WebException e)
{
Console.WriteLine("WebException raised!");
Console.WriteLine("\n{0}",e.Message);
Console.WriteLine("\n{0}",e.Status);
}
catch(Exception e)
{
Console.WriteLine("Exception raised!");
Console.WriteLine("Source :{0} " , e.Source);
Console.WriteLine("Message :{0} " , e.Message);
}
}
}
Class HttpWebRequest_Connection
Shared Sub Main()
Try
' Create a new 'HttpWebRequest' object for the specified Uri. Make sure that
' a default proxy is set if you are behind a firewall.
Dim myHttpWebRequest1 As HttpWebRequest = CType(WebRequest.Create("http://www.contoso.com"), HttpWebRequest)
myHttpWebRequest1.KeepAlive = False
' Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
Dim myHttpWebResponse1 As HttpWebResponse = CType(myHttpWebRequest1.GetResponse(), HttpWebResponse)
Console.WriteLine(ControlChars.Cr + "The HTTP request Headers for the first request are {0}", myHttpWebRequest1.Headers)
Console.WriteLine("Press Enter Key to Continue..........")
Console.Read()
Dim streamResponse As Stream = myHttpWebResponse1.GetResponseStream()
Dim streamRead As New StreamReader(streamResponse)
Dim readBuff(256) As [Char]
Dim count As Integer = streamRead.Read(readBuff, 0, 256)
Console.WriteLine("The contents of the Html page are......." + ControlChars.Cr)
While count > 0
Dim outputData As New [String](readBuff, 0, count)
Console.Write(outputData)
count = streamRead.Read(readBuff, 0, 256)
End While
' Close the Stream object.
streamResponse.Close()
streamRead.Close()
' Release the resources held by response object.
myHttpWebResponse1.Close()
Console.WriteLine()
' Create a new 'HttpWebRequest' object to the specified Uri.
Dim myHttpWebRequest2 As HttpWebRequest = CType(WebRequest.Create("http://www.contoso.com"), HttpWebRequest)
myHttpWebRequest2.Connection = "Close"
' Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
Dim myHttpWebResponse2 As HttpWebResponse = CType(myHttpWebRequest2.GetResponse(), HttpWebResponse)
' Release the resources held by response object.
myHttpWebResponse2.Close()
Console.WriteLine(ControlChars.Cr + "The Http RequestHeaders are " + ControlChars.Cr + "{0}", myHttpWebRequest2.Headers)
Console.WriteLine(ControlChars.Cr + "Press 'Enter' Key to Continue.........")
Console.Read()
Catch e As ArgumentException
Console.WriteLine(ControlChars.Cr + "The second HttpWebRequest object has raised an Argument Exception as 'Connection' Property is set to 'Close'")
Console.WriteLine(ControlChars.Cr + "{0}", e.Message)
Catch e As WebException
Console.WriteLine("WebException raised!")
Console.WriteLine(ControlChars.Cr + "{0}", e.Message)
Console.WriteLine(ControlChars.Cr + "{0}", e.Status)
Catch e As Exception
Console.WriteLine("Exception raised!")
Console.WriteLine("Source :{0} ", e.Source)
Console.WriteLine("Message : {0}", e.Message)
End Try
End Sub
End Class
Poznámky
Opatrnost
WebRequest
, HttpWebRequest
, ServicePoint
a WebClient
jsou zastaralé a neměli byste je používat pro nový vývoj. Místo toho použijte HttpClient.
Nastavte tuto vlastnost na true
odeslat hlavičku http Connection
s hodnotou Keep-alive. Aplikace používá KeepAlive k označení předvolby trvalých připojení. Pokud je vlastnost KeepAlivetrue
, aplikace vytvoří trvalá připojení k serverům, které je podporují.
Poznámka
Při použití protokolu HTTP/1.1 je Keep-Alive ve výchozím nastavení zapnutý. Nastavení KeepAlive na false
může vést k odeslání hlavičky Connection: Close
na server.