java8 stream list分组处理

public static void main(String[] args) throws IllegalAccessException {
        //   public Name(String nameCode, String cay, int sum, int count, int doub) {
        List<Name> excelDtoList = new ArrayList<>();
        Name testCar1 = new Name("431300000000","娄星区",1,2,3);
        Name testCar3 = new Name("431010000000","雨花区",1,2,3);
        Name testCar2 = new Name("431010000000","天心区",2,2,3);
        excelDtoList.add(testCar1);
        excelDtoList.add(testCar3);
        excelDtoList.add(testCar2);

        System.out.println("-------------list分组--------------");
        Map<String,List<Name>>map = excelDtoList.stream().collect(Collectors.groupingBy(Name::getNameCode));
        map.forEach((s, names) -> {
            System.out.println(s+" ：");
            names.stream().forEach(item->{
                System.out.println(item.toString());
            });
        });

        System.out.println("-------------list分组求和--------------");
        Map<String,Integer> mapSum = excelDtoList.stream()
                .collect(Collectors.groupingBy(Name::getNameCode,Collectors.summingInt(Name::getSum)));
        mapSum.forEach((s, integer) -> {
            System.out.print(s+":");
            System.out.println(integer);
        });
        System.out.println("-------------list去重--------------");
        //对象去重
        List<Name> distinctList = excelDtoList.stream().filter(distinctByKey(Name::getNameCode)).collect(Collectors.toList());
        distinctList.forEach(item->{
            System.out.println(item);
        });
    }
    public 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;
    }

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