递归查询

@Override
public List<CategoryEntity> listWithTree() {

    //1、查询出所有分类
    List<CategoryEntity> entities = super.baseMapper.selectList(null);

    //2、组装成父子的树形结构

    //2.1)、找到所有一级分类
    List<CategoryEntity> levelMenus = entities.stream()
            .filter(e -> e.getParentCid() == 0)
            .map((menu) -> {
                menu.setChildren(getChildrens(menu, entities));
                return menu;
            })
            .sorted(Comparator.comparingInt(menu -> (menu.getSort() == null ? 0 : menu.getSort())))
            .collect(Collectors.toList());

    return levelMenus;
}

//递归查找所有菜单的子菜单
private List<CategoryEntity> getChildrens(CategoryEntity root, List<CategoryEntity> all) {

    List<CategoryEntity> children = all.stream().filter(categoryEntity -> {
        return categoryEntity.getParentCid().equals(root.getCatId());
    }).map(categoryEntity -> {
        //1、找到子菜单(递归)
        categoryEntity.setChildren(getChildrens(categoryEntity, all));
        return categoryEntity;
    }).sorted(Comparator.comparingInt(menu -> (menu.getSort() == null ? 0 : menu.getSort()))).collect(Collectors.toList());

    return children;

}