后台管理系统中的三级分类制作

service
List<CategoryEntity> listWithTree();
实现类
@Override
    public List<CategoryEntity> listWithTree() {
        List<CategoryEntity> categoryEntityList = baseMapper.selectList(null);
        List<CategoryEntity> level1Menus = categoryEntityList.stream().filter(categoryEntity ->
                categoryEntity.getParentCid() == 0
        ).map(menu -> {
            menu.setChildren(getChildrens(menu, categoryEntityList));
            return menu;
        }).sorted((menu1, menu2) -> {
            return menu1.getSort() - menu2.getSort();
        }).collect(Collectors.toList());
        return level1Menus;
    }
    private List<CategoryEntity> getChildrens(CategoryEntity root, List<CategoryEntity> allList) {
        List<CategoryEntity> collect = allList.stream().filter(categoryEntity -> {
            return categoryEntity.getParentCid() == root.getCatId();
        }).map(categoryEntity -> {
            categoryEntity.setChildren(getChildrens(categoryEntity, allList));
            return categoryEntity;
        }).sorted((menu1, menu2) -> {
            return (menu1.getSort() == null ? 0 : menu1.getSort()) - (menu2.getSort() == null ? 0 : menu2.getSort());
        }).collect(Collectors.toList());
        return collect;
    }

@RequestMapping("/list")
public R list(){
    List<CategoryEntity> categoryEntityList = categoryService.listWithTree();
    return R.ok().put("data", categoryEntityList);
}