现在记录其中一种实现方式:
Map<String, String> item_id2title_map = item_conf_df.select("movieId", "title").collectAsList().stream()
.collect(Collectors.toMap(row -> row.get(0).toString(), row -> row.get(1).toString()));
Map<String, String> item_id2genres_map = item_conf_df.select("movieId", "genres").collectAsList().stream()
.collect(Collectors.toMap(row -> row.get(0).toString(), row -> row.get(1).toString()));