Simple file upload by using FileUpload control.

What I need:
1.User can upload only one file at a time.
2.No save file to disk; read it's content and then dispose it.
3.Only txt and csv file types are allowed.

Here is the aspx page

<asp:Panel ID="PanelUploadList" runat="server" ViewStateMode="Disabled">
    <hr />
    Please select a text file to upload:
    <asp:FileUpload ID="FileUpload1" runat="server" />
    <asp:RequiredFieldValidator ID="RequiredFieldValidatorFileUpload" runat="server"
        ControlToValidate="FileUpload1"
        ErrorMessage="Please select a file to upload!" Display="Dynamic">*asp:RequiredFieldValidator>
    <asp:RegularExpressionValidator ID="RegularExpressionValidatorFileUpload" runat="server"
        ControlToValidate="FileUpload1" ValidationExpression="^(([a-zA-Z]:)|(\\{2}\w+)\$?)(\\(\w[\w].*))+(.txt|.csv)$"
        ErrorMessage="Only txt and csv file types are allowed!">*asp:RegularExpressionValidator>
    <asp:Button ID="ButtonUpload" runat="server" OnClick="ButtonUpload_Click"
        Text="Upload" />
    <hr />
</asp:Panel>