通过Stream流的方式查询树结构

@Override
public List<CategoryEntity> listWithTree() {
    //1、查询所有的分类数据
    List<CategoryEntity> entities = categoryDao.selectList(null);

    //2、组装成父子的树形结构
    //2.1、找到所有的一级分类
    List<CategoryEntity> level1Menus = entities.stream().filter(s -> {
        boolean b = false;
        if (s.getParentCid() != null) {
            b = s.getParentCid() == 0;
        }
        return b;
    }).map((menu) -> {
        menu.setChildren(getChildrens(menu, entities));
        return menu;
    }).sorted((menu1, menu2) -> {
        return (menu1.getSort() == null ? 0 : menu1.getSort()) - (menu2.getSort() == null? 0 : menu2.getSort());
    }).collect(Collectors.toList());

    return level1Menus;
}

/**
 * 递归获取菜单类别的子节点
 * @param root 父节点
 * @param all 所有类别数据
 * @return
 */
private List<CategoryEntity> getChildrens(CategoryEntity root, List<CategoryEntity> all) {
    List<CategoryEntity> children = all.stream().filter(categoryEntity -> {
        return categoryEntity.getParentCid() == root.getCatId();
    }).map(categoryEntity -> {
        categoryEntity.setChildren(getChildrens(categoryEntity, all));
        return categoryEntity;
    }).sorted((menu1, menu2) -> {
        return (menu1.getSort() == null ? 0 : menu1.getSort()) - (menu2.getSort() == null? 0 : menu2.getSort());
    }).collect(Collectors.toList());
    return children;
}