Answer 1: Force open the wifi

Check this link on stackoverflow for details

Answer 2: Get the mac address by network interface

The below code will help get all mack addresses of the device.

private static String getMacAddress(String interfaceName) {
    try {
        Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
        while (interfaces.hasMoreElements()) {
            NetworkInterface networkInterface = interfaces.nextElement();

            if (TextUtils.equals(networkInterface.getName(), interfaceName)) {
                byte[] bytes = networkInterface.getHardwareAddress();
                StringBuilder builder = new StringBuilder();
                for (byte b : bytes) {
                    builder.append(String.format("%02X:", b));
                }

                if (builder.length() > 0) {
                    builder.deleteCharAt(builder.length() - 1);
                }

                return builder.toString();
            }
        }

        return "<EMPTY>";
    } catch (SocketException e) {
        Log.e(Constants.TAG, "Get Mac Address Error", e);
        return "<ERROR>";
    }
}

Use wlan0 if you want to get the WIFI MAC address, and eth0 if you want to get the ethernet MAC address.

public static String getEthernetMacAddress() {
    return getMacAddress("eth0");
}

public static String getWifiMacAddress() {
    return getMacAddress("wlan0");
}