How do I download a webpage into a stream in .NET

问题:

I know this should be a basic question but I am hitting a brick wall. I am looking to go to a URL/URI download the resulting string as if I had opened a file and then get it out into a String variable.

I have been stuffing about with IO.Stream and Net.httpxxx but haven't managed to get the elements to line up in the right way.

I get "the given path's format is not supported" from opening the page in the standard stream, because it's not in the local file system ... that bit i understand, the bit I don't get is ... how do I achieve the equivelent of:

Public Function GetWebPageAsString(pURL As String) As String
        Dim lStream As IO.StreamReader = New System.IO.StreamReader(pURL)
        Return lStream.ReadToEnd

End Function

回答1:

The short answer, in C#, looks like

using(System.Net.WebClient client = new System.Net.WebClient())
{
  string html = client.DownloadString("http://www.google.com");
}

回答2:

WebClient.OpenRead() might be what you're looking for.

Sample from the MSDN page linked above:

 Dim uriString as String
 uriString = "http://www.google.com"

 Dim myWebClient As New WebClient()

 Console.WriteLine("Accessing {0} ...", uriString)

 Dim myStream As Stream = myWebClient.OpenRead(uriString)

 Console.WriteLine(ControlChars.Cr + "Displaying Data :" + ControlChars.Cr)
 Dim sr As New StreamReader(myStream)
 Console.WriteLine(sr.ReadToEnd())

 myStream.Close()

回答3:

This function downloads any URI to a file. You could easily adapt it to put it into a string var:

public static int DownloadFile(String remoteFilename, String localFilename, bool enforceXmlSafe)
{
// Function will return the number of bytes processed
// to the caller. Initialize to 0 here.
int bytesProcessed = 0;

// Assign values to these objects here so that they can
// be referenced in the finally block
Stream remoteStream = null;
Stream localStream = null;
WebResponse response = null;            

// Use a try/catch/finally block as both the WebRequest and Stream
// classes throw exceptions upon error
try
{
    // Create a request for the specified remote file name
    WebRequest request = WebRequest.Create(remoteFilename);
    if (request != null)
    {
        // Send the request to the server and retrieve the
        // WebResponse object 
        response = request.GetResponse();
        if (response != null)
        {
            // Once the WebResponse object has been retrieved,
            // get the stream object associated with the response's data
            remoteStream = response.GetResponseStream();

            // Create the local file
            if (localFilename != null)
                localStream = File.Create(localFilename);
            else
                localStream = new MemoryStream();

            // Allocate a 1k buffer
            byte[] buffer = new byte[1024];
            int bytesRead;

            // Simple do/while loop to read from stream until
            // no bytes are returned
            do
            {
                // Read data (up to 1k) from the stream
                bytesRead = remoteStream.Read(buffer, 0, buffer.Length);

                // Write the data to the local file
                localStream.Write(buffer, 0, bytesRead);

                // Increment total bytes processed
                bytesProcessed += bytesRead;
            } while (bytesRead > 0);
        }
    }
}
catch (Exception e)
{
    Console.WriteLine(e.Message);
}
finally
{
    // Close the response and streams objects here 
    // to make sure they're closed even if an exception
    // is thrown at some point
    if (response != null) response.Close();
    if (remoteStream != null) remoteStream.Close();
    if (localStream != null) localStream.Close();
}

// Return total bytes processed to caller.
return bytesProcessed;
}