code: public ServiceFuture<VpnConnectionInner> getAsync(String resourceGroupName, String gatewayName, String connectionName, final ServiceCallback<VpnConnectionInner> serviceCallback) {
          return ServiceFuture.fromResponse(getWithServiceResponseAsync(resourceGroupName, gatewayName, connectionName), serviceCallback);
      }
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.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object