code: public ServiceFuture<List<ExpressRouteLinkInner>> listAsync(final String resourceGroupName, final String expressRoutePortName, final ListOperationCallback<ExpressRouteLinkInner> serviceCallback) {
          return AzureServiceFuture.fromPageResponse(
              listSinglePageAsync(resourceGroupName, expressRoutePortName),
              new Func1<String, Observable<ServiceResponse<Page<ExpressRouteLinkInner>>>>() {
                  @Override
                  public Observable<ServiceResponse<Page<ExpressRouteLinkInner>>> call(String nextPageLink) {
                      return listNextSinglePageAsync(nextPageLink);
                  }
              },
              serviceCallback);
      }
docs: Retrieve the ExpressRouteLink sub-resources of the specified ExpressRoutePort resource.
  
  @param resourceGroupName The name of the resource group.
  @param expressRoutePortName The name of the ExpressRoutePort resource.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object