【阅己书城】递归组装菜单

1、背景
商品三级分类
2、代码

    /**
     * 查询所有分类以及子分类，以树形结构组装起来
     */
    public List<CategoryEntity> listWithTree() {

        // 查出所有分类
        List<CategoryEntity> categoryEntities = baseMapper.selectList(null);
        List<CategoryEntity> level1Menus = categoryEntities.stream().filter(categoryEntity ->
                categoryEntity.getParentCid() == 0
        ).map(menu -> {
            menu.setChildren(getChildrens(menu, categoryEntities));
            return menu;
        }).sorted((menu1, menu2) -> {
            return (menu1.getSort() == null ? 0 : menu1.getSort()) - (menu2.getSort() == null ? 0 : menu2.getSort());
        }).collect(Collectors.toList());

        // 组装出父子的树形结构
        return level1Menus;
    }



    /**
     * 递归查找所有菜单的子菜单
     *
     * @param root
     * @param all
     * @return
     */
    private List<CategoryEntity> getChildrens(CategoryEntity root, List<CategoryEntity> all) {
        List<CategoryEntity> children = all.stream().filter(categoryEntity -> {
            return categoryEntity.getParentCid().equals(root.getCatId());
        }).map(categoryEntity -> {
            // 找到子菜单
            categoryEntity.setChildren(getChildrens(categoryEntity, all));
            return categoryEntity;
        }).sorted((menu1, menu2) -> {
            // 排序
            return (menu1.getSort() == null ? 0 : menu1.getSort()) - (menu2.getSort() == null ? 0 : menu2.getSort());
        }).collect(Collectors.toList());
        return children;
    }