code: public ServiceFuture<VpnSiteInner> getByResourceGroupAsync(String resourceGroupName, String vpnSiteName, final ServiceCallback<VpnSiteInner> serviceCallback) {
          return ServiceFuture.fromResponse(getByResourceGroupWithServiceResponseAsync(resourceGroupName, vpnSiteName), serviceCallback);
      }
docs: Retrieves the details of a VPNsite.
  
  @param resourceGroupName The resource group name of the VpnSite.
  @param vpnSiteName The name of the VpnSite being retrieved.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object