Find which Network a VirtualNetworkGateway is attached to

I'm trying to find either a list of attached VGWs given a VNet, or the attached VNet given a VGW. I'm using the java api library here: https://azure.github.io/azure-sdk-for-java/

I need to either start with a Network object in and end up with a VirtualNetworkGateway object, or vice versa. Either solution is find. Both classes are found in the com.microsoft.azure.management.network package.