code: public Observable<ActivityInner> getAsync(String resourceGroupName, String automationAccountName, String moduleName, String activityName) {
          return getWithServiceResponseAsync(resourceGroupName, automationAccountName, moduleName, activityName).map(new Func1<ServiceResponse<ActivityInner>, ActivityInner>() {
              @Override
              public ActivityInner call(ServiceResponse<ActivityInner> response) {
                  return response.body();
              }
          });
      }
docs: Retrieve the activity in the module identified by module name and activity name.
  
  @param resourceGroupName Name of an Azure Resource group.
  @param automationAccountName The name of the automation account.
  @param moduleName The name of module.
  @param activityName The name of activity.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the ActivityInner object