code: public ServiceFuture<List<P2SVpnServerConfigurationInner>> listByVirtualWanAsync(final String resourceGroupName, final String virtualWanName, final ListOperationCallback<P2SVpnServerConfigurationInner> serviceCallback) {
          return AzureServiceFuture.fromPageResponse(
              listByVirtualWanSinglePageAsync(resourceGroupName, virtualWanName),
              new Func1<String, Observable<ServiceResponse<Page<P2SVpnServerConfigurationInner>>>>() {
                  @Override
                  public Observable<ServiceResponse<Page<P2SVpnServerConfigurationInner>>> call(String nextPageLink) {
                      return listByVirtualWanNextSinglePageAsync(nextPageLink);
                  }
              },
              serviceCallback);
      }
docs: Retrieves all P2SVpnServerConfigurations for a particular VirtualWan.
  
  @param resourceGroupName The resource group name of the VirtualWan.
  @param virtualWanName The name of the VirtualWan.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object