Validate URL Address in ASP.NET

In aspx page:

<table>
        <tr>
            <td colspan="2" align="center">
                <asp:Label ID="lblURL" runat="server" Font-Bold="true" ForeColor="Red"></asp:Label>
            </td>
        </tr>
        <tr>
            <td>
                <strong>Enter URL:</strong>
            </td>
            <td>
                <asp:TextBox ID="txtUrlAddress" runat="server"></asp:TextBox>
                <asp:RequiredFieldValidator ID="RFV_txtUrlAddress" runat="server" ControlToValidate="txtUrlAddress"
                    Display="None" SetFocusOnError="true" ErrorMessage="Please Enter URL" ValidationGroup="Submitgp"></asp:RequiredFieldValidator>
                <ajaxToolkit:ValidatorCalloutExtender ID="VCE1_txtUrlAddress" runat="server" TargetControlID="RFV_txtUrlAddress">
                </ajaxToolkit:ValidatorCalloutExtender>
                <asp:RegularExpressionValidator ID="REV_txtUrlAddress" runat="server" ControlToValidate="txtUrlAddress"
                    ValidationExpression="http(s)?://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?" ValidationGroup="Submitgp"
                    Display="None" ErrorMessage="Please Enter Valid URL" SetFocusOnError="true"></asp:RegularExpressionValidator>
                <ajaxToolkit:ValidatorCalloutExtender ID="VCE2_txtUrlAddress" runat="server" TargetControlID="REV_txtUrlAddress">
                </ajaxToolkit:ValidatorCalloutExtender>
            </td>
        </tr>
        <tr>
            <td colspan="2">
                <asp:Button ID="btnSubmit" runat="server" Text="Submit" ValidationGroup="Submitgp"
                    OnClick="btnSubmit_Click" />
            </td>
        </tr>
    </table>

In aspx.cs code:

 protected void btnSubmit_Click(object sender, EventArgs e)
    {
        lblURL.Text = "Your URL is:" + txtUrlAddress.Text;
    }