@Override
  public <RequestT, ResponseT, MetadataT>
      OperationCallable<RequestT, ResponseT, MetadataT> createOperationCallable(
          HttpJsonCallSettings<RequestT, Operation> httpJsonCallSettings,
          OperationCallSettings<RequestT, ResponseT, MetadataT> callSettings,
          ClientContext clientContext,
          OperationsStub operationsStub) {
    UnaryCallable<RequestT, Operation> innerCallable =
        HttpJsonCallableFactory.createBaseUnaryCallable(
            httpJsonCallSettings, callSettings.getInitialCallSettings(), clientContext);
    HttpJsonOperationSnapshotCallable<RequestT, Operation> initialCallable =
        new HttpJsonOperationSnapshotCallable<RequestT, Operation>(
            innerCallable,
            httpJsonCallSettings.getMethodDescriptor().getOperationSnapshotFactory());
    return HttpJsonCallableFactory.createOperationCallable(
        callSettings, clientContext, operationsStub.longRunningClient(), initialCallable);
  }
REST callable factory implementation for the Completion service API.

<p>This class is for advanced usage.
java-talent/google-cloud-talent/src/main/java/com/google/cloud/talent/v4beta1/stub/HttpJsonCompletionCallableFactory.java