How to: Send Data Using the WebRequest Class


The following procedure describes the steps used to send data to a server. This procedure is commonly used to post data to a Web page.

To send data to a host server

  1. Create a WebRequest instance by calling Create with the URI of the resource that accepts data, for example, a script or ASP.NET page.

    Dim request as WebRequest = WebRequest.Create("")  
    System_CAPS_ICON_note.jpg Note

    The .NET Framework provides protocol-specific classes derived from WebRequest and WebResponse for URIs that begin with "http:", "https:'', "ftp:", and "file:". To access resources using other protocols, you must implement protocol-specific classes that derive from WebRequest and WebResponse. For more information, see Programming Pluggable Protocols .

  2. Set any property values that you need in the WebRequest. For example, to enable authentication, set the Credentials property to an instance of the NetworkCredential class.

    request.Credentials = CredentialCache.DefaultCredentials  

    In most cases, the WebRequest instance itself is sufficient to send data. However, if you need to set protocol-specific properties, you must cast the WebRequest to the protocol-specific type. For example, to access the HTTP-specific properties of HttpWebRequest, cast the WebRequest to an HttpWebRequest reference. The following code example shows how to set the HTTP-specific UserAgent property.

    Ctype(request,HttpWebRequest).UserAgent = ".NET Framework Example Client"  
  3. Specify a protocol method that permits data to be sent with a request, such as the HTTP POST method.

    request.Method = "POST"  
  4. Set the ContentLength property.

    request.ContentLength = byteArray.Length  
  5. Set the ContentType property to an appropriate value.

    request.ContentType = "application/x-www-form-urlencoded"  
  6. Get the stream that holds request data by calling the GetRequestStream method.

    Stream dataStream = request.GetRequestStream ()  
  7. Write the data to the Stream object returned by this method.

    dataStream.Write (byteArray, 0, byteArray.Length)  
  8. Close the request stream by calling the Stream.Close method.

    dataStream.Close ()  
  9. Send the request to the server by calling GetResponse. This method returns an object containing the server's response. The returned WebResponse object's type is determined by the scheme of the request's URI.

    Dim response As WebResponse = request.GetResponse()  
    System_CAPS_ICON_note.jpg Note

    After you are finished with a WebResponse object, you must close it by calling the Close method. Alternatively, if you have gotten the response stream from the response object, you can close the stream by calling the Stream.Close method. If you do not close the response or the stream, your application can run out of connections to the server and become unable to process additional requests.

  10. You can access the properties of the WebResponse or cast the WebResponse to a protocol-specific instance to read protocol-specific properties. For example, to access the HTTP-specific properties of HttpWebResponse, cast the WebResponse to an HttpWebResponse reference.

    Console.WriteLine(CType(response, HttpWebResponse).StatusDescription)  
  11. To get the stream containing response data sent by the server, call the GetResponseStream method of the WebResponse.

    Dim data As Stream = response.GetResponseStream  
  12. After reading the data from the response, you must either close the response stream using the Stream.Close method or close the response using the WebResponse.Close method. It is not necessary to call the Close method on both the response stream and the WebResponse, but doing so is not harmful.

Imports System  
Imports System.IO  
Imports System.Net  
Imports System.Text  
Namespace Examples.System.Net  
    Public Class WebRequestPostExample  
        Public Shared Sub Main()  
            ' Create a request using a URL that can receive a post.   
            Dim request As WebRequest = WebRequest.Create(" ")  
            ' Set the Method property of the request to POST.  
            request.Method = "POST"  
            ' Create POST data and convert it to a byte array.  
            Dim postData As String = "This is a test that posts this string to a Web server."  
            Dim byteArray As Byte() = Encoding.UTF8.GetBytes(postData)  
            ' Set the ContentType property of the WebRequest.  
            request.ContentType = "application/x-www-form-urlencoded"  
            ' Set the ContentLength property of the WebRequest.  
            request.ContentLength = byteArray.Length  
            ' Get the request stream.  
            Dim dataStream As Stream = request.GetRequestStream()  
            ' Write the data to the request stream.  
            dataStream.Write(byteArray, 0, byteArray.Length)  
            ' Close the Stream object.  
            ' Get the response.  
            Dim response As WebResponse = request.GetResponse()  
            ' Display the status.  
            Console.WriteLine(CType(response, HttpWebResponse).StatusDescription)  
            ' Get the stream containing content returned by the server.  
            dataStream = response.GetResponseStream()  
            ' Open the stream using a StreamReader for easy access.  
            Dim reader As New StreamReader(dataStream)  
            ' Read the content.  
            Dim responseFromServer As String = reader.ReadToEnd()  
            ' Display the content.  
            ' Clean up the streams.  
        End Sub  
    End Class  
End Namespace  

Creating Internet Requests
Using Streams on the Network
Accessing the Internet Through a Proxy
Requesting Data
How to: Request Data Using the WebRequest Class