code: public Observable<VpnConnectionInner> getAsync(String resourceGroupName, String gatewayName, String connectionName) {
          return getWithServiceResponseAsync(resourceGroupName, gatewayName, connectionName).map(new Func1<ServiceResponse<VpnConnectionInner>, VpnConnectionInner>() {
              @Override
              public VpnConnectionInner call(ServiceResponse<VpnConnectionInner> response) {
                  return response.body();
              }
          });
      }
docs: Retrieves the details of a vpn connection.
  
  @param resourceGroupName The resource group name of the VpnGateway.
  @param gatewayName The name of the gateway.
  @param connectionName The name of the vpn connection.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the VpnConnectionInner object