继上一篇博客 实战拉姆达表达式（雷神nb！！！）

@Override public List<CategoryEntity> listTree() { //查出所有分类 List<CategoryEntity> categoryEntities = baseMapper.selectList(null); //2.组装父子的树形结构 //2.1找到所有树形分类的一级分类 List<CategoryEntity> level1Menu = categoryEntities.stream().filter((CategoryEntity) -> { return CategoryEntity.getParentCid() == 0; }).map((menu)->{ menu.setChildren(getChildren(menu,categoryEntities)); return menu; }).sorted((menu1,menu2)->{ return (menu1.getSort()==null?0:menu1.getSort())-(menu2.getSort()==null?0:menu2.getSort()); }).collect(Collectors.toList()); return level1Menu; } //递归查找所有菜单的子菜单 private List<CategoryEntity>getChildren(CategoryEntity root, List<CategoryEntity>all) { List<CategoryEntity> children = all.stream().filter(categoryEntity -> { return categoryEntity.getParentCid() == root.getCatId(); }).map(categoryEntity -> { //1.找到子菜单 categoryEntity.setChildren(getChildren(categoryEntity,all)); return categoryEntity; }).sorted((menu1,menu2)->{ //2.菜单排序 return (menu1.getSort()==null?0:menu1.getSort())-(menu2.getSort()==null?0:menu2.getSort()); }).collect(Collectors.toList()); return children; }