code: public Observable<ApplicationGatewayBackendHealthInner> beginBackendHealthAsync(String resourceGroupName, String applicationGatewayName, String expand) {
          return beginBackendHealthWithServiceResponseAsync(resourceGroupName, applicationGatewayName, expand).map(new Func1<ServiceResponse<ApplicationGatewayBackendHealthInner>, ApplicationGatewayBackendHealthInner>() {
              @Override
              public ApplicationGatewayBackendHealthInner call(ServiceResponse<ApplicationGatewayBackendHealthInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets the backend health of the specified application gateway in a resource group.
  
  @param resourceGroupName The name of the resource group.
  @param applicationGatewayName The name of the application gateway.
  @param expand Expands BackendAddressPool and BackendHttpSettings referenced in backend health.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the ApplicationGatewayBackendHealthInner object