[大数据]java8 List＜Map＞根据某属性去除重复保留顺序

private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
    Map<Object, Boolean> seen = new ConcurrentHashMap<>();
    return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
}

public static void main(String[] args) {
    List<Map<String, Object>> wordItems = new ArrayList<>();
    Map<String, Object> map1 = new HashMap();
    map1.put("a",2);
    map1.put("b",1);
    map1.put("c",2);
    wordItems.add(map1);
    Map<String, Object> map2 = new HashMap();
    map2.put("a",21);
    map2.put("b",2);
    wordItems.add(map2);
    Map<String, Object> map3= new HashMap();
    map3.put("a",2);
    map3.put("b",3);
    map3.put("c",3);
    wordItems.add(map3);
    Map<String, Object> map4= new HashMap();
    map4.put("b",4);
    map4.put("c",3);
    wordItems.add(map4);
    Map<String, Object> map5= new HashMap();
    map4.put("b",5);
    map4.put("a",5);
    map4.put("c",5);
    wordItems.add(map5);
    wordItems = wordItems.stream().filter(keyMap -> keyMap.containsKey("a")).filter(distinctByKey(map -> map.get("a"))).collect(Collectors.toList());
    System.out.println(JSONUtil.toJsonStr(wordItems));
}

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