code: public ServiceFuture<VnetGatewayInner> updateVnetGatewayAsync(String resourceGroupName, String name, String vnetName, String gatewayName, VnetGatewayInner connectionEnvelope, final ServiceCallback<VnetGatewayInner> serviceCallback) {
          return ServiceFuture.fromResponse(updateVnetGatewayWithServiceResponseAsync(resourceGroupName, name, vnetName, gatewayName, connectionEnvelope), serviceCallback);
      }
docs: Update a Virtual Network gateway.
  Update a Virtual Network gateway.
  
  @param resourceGroupName Name of the resource group to which the resource belongs.
  @param name Name of the App Service plan.
  @param vnetName Name of the Virtual Network.
  @param gatewayName Name of the gateway. Only the 'primary' gateway is supported.
  @param connectionEnvelope Definition of the gateway.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object