code: public Observable<P2SVpnGatewayInner> getByResourceGroupAsync(String resourceGroupName, String gatewayName) {
          return getByResourceGroupWithServiceResponseAsync(resourceGroupName, gatewayName).map(new Func1<ServiceResponse<P2SVpnGatewayInner>, P2SVpnGatewayInner>() {
              @Override
              public P2SVpnGatewayInner call(ServiceResponse<P2SVpnGatewayInner> response) {
                  return response.body();
              }
          });
      }
docs: Retrieves the details of a virtual wan p2s vpn gateway.
  
  @param resourceGroupName The resource group name of the P2SVpnGateway.
  @param gatewayName The name of the gateway.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the P2SVpnGatewayInner object