（一）Stream 好用

　　

@Override
public List<CategoryEntity> listWithTree() {

    //1 查出所有分类
    List<CategoryEntity> categoryEntities = 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> level1Menus = categoryEntities.stream().filter((categoryEntitie) -> {
        return categoryEntitie.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());

    return level1Menus;
}


private List<CategoryEntity> getChildrens(CategoryEntity root,List<CategoryEntity> all){

    List<CategoryEntity> children = all.stream().filter(categoryEntity -> {
        return categoryEntity.getParentCid() == root.getCatId();
    }).map((categoryEntity) -> {
        //找子菜单 递归
        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;
}

 

 

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