code: public Observable<SubnetInner> getAsync(String resourceGroupName, String virtualNetworkName, String subnetName) {
          return getWithServiceResponseAsync(resourceGroupName, virtualNetworkName, subnetName).map(new Func1<ServiceResponse<SubnetInner>, SubnetInner>() {
              @Override
              public SubnetInner call(ServiceResponse<SubnetInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets the specified subnet by virtual network and resource group.
  
  @param resourceGroupName The name of the resource group.
  @param virtualNetworkName The name of the virtual network.
  @param subnetName The name of the subnet.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the SubnetInner object