code: public Observable<RouteFilterRuleInner> getAsync(String resourceGroupName, String routeFilterName, String ruleName) {
          return getWithServiceResponseAsync(resourceGroupName, routeFilterName, ruleName).map(new Func1<ServiceResponse<RouteFilterRuleInner>, RouteFilterRuleInner>() {
              @Override
              public RouteFilterRuleInner call(ServiceResponse<RouteFilterRuleInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets the specified rule from a route filter.
  
  @param resourceGroupName The name of the resource group.
  @param routeFilterName The name of the route filter.
  @param ruleName The name of the rule.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the RouteFilterRuleInner object