I have used a asp.net file upload control. This control exposes some properties which can be used to our advantage.

1. Content type – This returns the content type of the uploaded file. You can use this to make sure the content being uploaded is really an excel type file.

2. InputStream – This returns the stream object into which the contents of the file are loaded. This stream can be loded into a stream reader and you have the contents line by line.
 

        'Code to upload csv file intp stream reader
        Dim streamReader As System.IO.StreamReader
        Dim fileUpload As System.Web.UI.WebControls.FileUpload = Me.FileUpload 'This control has to be added to the web form
        Dim filePath As String = System.IO.Path.GetFileName(fileUpload.PostedFile.FileName)
        If Not filePath.Trim().Equals(String.Empty) Then
            If fileUpload.PostedFile.ContentType.Equals("application/vnd.ms-excel") Then
                If (fileUpload.PostedFile.InputStream.Length > 0) Then
                    If (fileUpload.PostedFile.FileName.ToLower().EndsWith(".csv")) Then
                        ' Read and display the lines from the file until the end of the file is reached.
                        streamReader = New System.IO.StreamReader(fileUpload.PostedFile.InputStream)
                        streamReader.Close()
                    End If
                End If
            End If
        End If
        '----Code to read the stream reader line by line
        While Not streamReader.EndOfStream
            Dim strEmployeeIncreases As String = streamReader.ReadLine()
        End While
        'Make sure you close the stream reader after reading all the data using the following line of code to free up system
        streamReader.Close()
        'Also one more tip: If you want to skip to the top of the stream reader at any point of time, you can use
        streamReader.BaseStream.Seek(0, System.IO.SeekOrigin.Begin)