/**
 * 查询所有分类,按顺序显示
 * 显示出树状
 * @return
 */
public List<DealCategory> getCategories() {
    List<DealCategory> dealCategories = getAllWithoutDeleted();//从缓存或数据库中查询全部
    //JDK8的stream处理,把根分类区分出来
    List<DealCategory> roots = dealCategories.stream().filter(dealCategory -> (dealCategory.getParentId() == 0)).collect(Collectors.toList());
    //对跟分类进行排序
    roots.sort(new Comparator<DealCategory>() {
        @Override
        public int compare(DealCategory o1, DealCategory o2) {
            return o1.getOrderNum() > o2.getOrderNum() ? 1 : -1;
        }
    });

    //把非根分类区分出来
    List<DealCategory> subs = dealCategories.stream().filter(dealCategory -> (dealCategory.getParentId() != 0)).collect(Collectors.toList());

    //递归构建结构化的分类信息
    roots.forEach(root -> buildSubs(root, subs));
    return roots;
}

/**
 * 递归构建
 * @param parent
 * @param subs
 */
private void buildSubs(DealCategory parent, List<DealCategory> subs) {
    List<DealCategory> children = subs.stream().filter(sub -> (sub.getParentId() == parent.getId())).collect(Collectors.toList());
    if (!CollectionUtils.isEmpty(children)) {//有子分类的情况
        parent.setChildren(children);
        children.forEach(child -> buildSubs(child, subs));//再次递归构建
    }
}