list 类型转换 Map

/**
 * list 类型转换
 *
 * @param list      source
 * @param keyMapper keyMapper
 * @param <T>       T
 * @param <K>       K
 * @return list
 */
public static <T, K> Map<K, List<T>> groupBy(List<T> list, Function<T, K> keyMapper) {
    if (CollectionUtils.isEmpty(list)) {
        return Collections.emptyMap();
    }
    return list.stream().collect(Collectors.groupingBy(keyMapper));
}