Java8组对象列表,其中包含列表

我宁愿这样做,

private static final String DELIMITER = "-";

Map<String, List<Favorite>> favsByGroup = favGroups.stream()
       .collect(Collectors.groupingBy(g -> g.getId() + DELIMITER + g.getUserId() + DELIMITER + g.getName(),
            Collectors.flatMapping(fg -> fg.getFavorites().stream(), Collectors.toList())));
List<FavoriteGroup> mergedFavoriteGroups = favsByGroup.entrySet().stream()
    .map(e -> new FavoriteGroup(Integer.parseInt(e.getKey().split(DELIMITER)[0]),
        e.getKey().split(DELIMITER)[1], e.getKey().split(DELIMITER)[2], e.getValue()))
    .collect(Collectors.toList());

首先创建一个映射,其中包含 FavoriteGroup 作为关键和关键 List Favorite 实例作为值。然后,对于地图中的每个条目,我将创建一个新的 通过解码键并按原样传递值。作为最后一步 collect

试试这个:-

favoriteGroups.stream()
        .collect(Collectors.toMap(FavoriteGroup::getId, Function.identity(), (fg1, fg2) -> {
            //This will modify the original object(s). If you don't want that, then you'll have to clone the object and set favorites.
            fg1.setFavorites(Stream.concat(fg1.getFavorites().stream(), fg2.getFavorites().stream())
                    .collect(Collectors.toList()));
            return fg1;
        }))
        .values();

这将返回类型为的对象 Collection<FavoriteGroup> ,您可以对其进行迭代。如果你想把它转换回 List List<FavoriteGroup> list = new ArrayList<>(favoriteGroupsCollection); .