HttpWebRequest.KeepAlive 属性

定义

获取或设置一个值,该值指示是否与 Internet 资源建立持续型连接。Gets or sets a value that indicates whether to make a persistent connection to the Internet resource.

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

属性值

如果对 Internet 资源的请求所包含的 true HTTP 标头带有 Keep-alive 这一值,则为 Connection;否则为 falsetrue if the request to the Internet resource should contain a Connection HTTP header with the value Keep-alive; otherwise, false. 默认值为 trueThe default is true.

示例

下面的代码示例将 KeepAlive 属性设置为 false,以避免与 Internet 资源建立持续连接。The following code example sets the KeepAlive property to false to avoid establishing a persistent connection with the Internet resource.

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

注解

将此属性设置为 "true" 以发送 Connection HTTP 标头,并将值保持为活动状态。Set this property to true to send a Connection HTTP header with the value Keep-alive. 应用程序使用 KeepAlive 指示持久性连接的首选项。An application uses KeepAlive to indicate a preference for persistent connections. trueKeepAlive 属性时,应用程序会与支持它们的服务器建立持久连接。When the KeepAlive property is true, the application makes persistent connections to the servers that support them.

备注

使用 HTTP/1.1 时,默认情况下,keep-alive 处于开启状态。When using HTTP/1.1, Keep-Alive is on by default. KeepAlive 设置为 false 可能会导致向服务器发送 Connection: Close 标头。Setting KeepAlive to false may result in sending a Connection: Close header to the server.

适用于