List<Map>聚合为单个Map<List>

@Test
void testReducing() {
    Set<Map<String, Integer>> nameScoreMapList = Stream.of(
            new HashMap<String, Integer>() {{
                put("苏格拉底", 1);
                put("特拉叙马霍斯", 3);
            }},
            Collections.singletonMap("苏格拉底", 2),
            Collections.singletonMap("特拉叙马霍斯", 1),
            Collections.singletonMap("特拉叙马霍斯", 2)
    ).collect(java.util.stream.Collectors.toSet());
    Collector<Map<String, Integer>, ?, Map<String, List<Integer>>> reducing = Collectors.reducing(new HashMap<>(),
            value -> {
                Map<String, List<Integer>> result = new HashMap<>();
                value.forEach((k, v) -> result.computeIfAbsent(k, i -> new ArrayList<>()).add(v));
                return result;
            }, (l, r) -> {
                r.forEach((k, v) -> l.computeIfAbsent(k, i -> new ArrayList<>()).addAll(v));
                return l;
            }
    );
    Assertions.assertEquals(new HashMap<String, List<Integer>>() {{
        put("苏格拉底", Arrays.asList(1, 2));
        put("特拉叙马霍斯", Arrays.asList(3, 1, 2));
    }}, nameScoreMapList.stream().collect(reducing));
}