asyncdf.java

DataFetcher userDataFetcher = new DataFetcher() {
    @Override
    public Object get(DataFetchingEnvironment environment) {
        CompletableFuture<User> userPromise = CompletableFuture.supplyAsync(
                () -> {
                    return fetchUserFromDatabase(environment.getArgument("userId"));
                });
        return userPromise;
    }
};