统一排序

多个字段按照同一逻辑排序

public enum SortEnum {
    ASC {
        @Override
        @SafeVarargs
        public final <T, V extends Comparable<V>> void sort(List<T> list, Function<T, V>... sortKeys) {
            Comparator<T> comparators = Stream.of(sortKeys)
                    .map(Comparator::comparing)
                    .reduce(Comparator::thenComparing)
                    .orElseThrow(IllegalArgumentException::new);
            list.sort(comparators);
        }
    },

    DESC {
        @Override
        @SafeVarargs
        public final <T, V extends Comparable<V>> void sort(List<T> list, Function<T, V>... sortKeys) {
            Comparator<T> comparators = Stream.of(sortKeys)
                    .map(key -> Comparator.comparing(key, Comparator.reverseOrder())) // 降序
                    .reduce(Comparator::thenComparing)
                    .orElseThrow(IllegalArgumentException::new);
            list.sort(comparators);
        }
    };

    public abstract <T, V extends Comparable<V>> void sort(List<T> list, Function<T, V>... sortKey);
}

运行结果如下：

  public static void main(String[] args) {
        @Data
        @AllArgsConstructor
        @NoArgsConstructor
        class M {
            private int a;
            private int b;
            private int c;
        }
        List<M> list = new ArrayList<>();
        list.add(new M(3, 2, 1));
        list.add(new M(3, 3, 2));
        list.add(new M(2, 1, 3));
        SortEnum.ASC.sort(list, M::getA, M::getB);
        System.out.println(list);
    }
[M(a=2, b=1, c=3), M(a=3, b=2, c=1), M(a=3, b=3, c=2)]

组合排序

自定义选择排序的字段，并选择升降排序。

public enum SortEnum {
    ASC {
        @Override
        public <T, V extends Comparable<V>> Comparator<T> getComparator(Function<T, V> sortKey) {
            return Comparator.comparing(sortKey);
        }
    },

    DESC {
        @Override
        public <T, V extends Comparable<V>> Comparator<T> getComparator(Function<T, V> sortKey) {
            return Comparator.comparing(sortKey, Comparator.reverseOrder());
        }
    };

    public abstract <T, V extends Comparable<V>> Comparator<T> getComparator(Function<T, V> sortKey);

    private static <T> SortBuilder<T> build(List<T> list) {
        return new SortBuilder<>(list);
    }

    private static class SortBuilder<T> {
        private final List<Comparator<T>> comparators = new ArrayList<>();
        private final List<T> list;

        public SortBuilder(List<T> list) {
            this.list = list;
        }

        public <V extends Comparable<V>> SortBuilder<T> add(Function<T, V> sortKey, SortEnum order) {
            comparators.add(order.getComparator(sortKey));
            return this;
        }

        public void sort() {
            Comparator<T> combinedComparator = comparators.stream()
                    .reduce(Comparator::thenComparing)
                    .orElseThrow(IllegalArgumentException::new);
            list.sort(combinedComparator);
        }
    }
}

运行结果如下：

    public static void main(String[] args) {
        @Data
        @AllArgsConstructor
        @NoArgsConstructor
        class M {
            private int a;
            private int b;
            private int c;
        }
        List<M> list = new ArrayList<>();
        list.add(new M(3, 2, 1));
        list.add(new M(3, 3, 2));
        list.add(new M(2, 1, 3));
        SortEnum.build(list)
                .add(M::getA, SortEnum.ASC)
                .add(M::getB, SortEnum.DESC)
                .sort();
        System.out.println(list);
    }
    //[M(a=2, b=1, c=3), M(a=3, b=3, c=2), M(a=3, b=2, c=1)]