Java Stream 将 List 转换为 Map

Question

我有一堂课PlayerAndCountry：

class PlayerAndCountry {
    private Country country;
    private Player player;
}

还有一个List<PlayerAndCountry>

我想要这样的最终地图：Map<Country,List<Player>>

我知道如何获取Map<Country, List<PlayerAndCountry>>，但不知道Map<Country,List<Player>>

Answer 1

你需要使用Collectors.mapping来实现它：

Map<Country, List<Player>> collect = list.stream()
        .collect(Collectors.groupingBy(PlayerAndCountry::getCountry,
                Collectors.mapping(PlayerAndCountry::getPlayer, Collectors.toList()))
        );