java后端操作树结构

一、树结构的三种组装方式(递归.双层for循环,map)

（1）递归
普通递归方法

 public Result getBmsMenuList(UserSessionVO userSessionInfo) {         // 查询顶级节点菜单         List<BmsMenuVO> bmsMenuVOList = bmsMenuDao.selectBmsMenuList(new BmsMenuQueryConditionVO());          for (BmsMenuVO bmsMenuVO : bmsMenuVOList) {             getBmsMenuListByRecursion(bmsMenuVO);         }          return Result.createWithModels(null, bmsMenuVOList);     }   private void getBmsMenuListByRecursion(BmsMenuVO bmsMenuVO) {         List<BmsMenuVO> bmsMenuVOS = bmsMenuDao.selectBmsMenuList(new BmsMenuQueryConditionVO().setParentId(bmsMenuVO.getId()));         if (CollectionUtils.isEmpty(bmsMenuVOS)) {             return;         }         bmsMenuVO.setChildBmsMenuList(bmsMenuVOS);         for (BmsMenuVO menuVO : bmsMenuVOS) {             getBmsMenuListByRecursion(menuVO);         } } 

stream流递归方法

//获取父节点 List<TreeSelect> collect = trees.stream().filter(m -> m.getParentId() == 0).map(     (m) -> {         m.setChildren(getChildrenList(m, trees));         return m;     } ).collect(Collectors.toList());       /**      * 获取子节点列表      * @param tree      * @param list      * @return      */     public static List<TreeSelect> getChildrenList(TreeSelect tree, List<TreeSelect> list){         List<TreeSelect> children = list.stream().filter(item -> Objects.equals(item.getParentId(), tree.getId())).map(                 (item) -> {                     item.setChildren(getChildrenList(item, list));                     return item;                 }         ).collect(Collectors.toList());         return children;     } 

（2）双层for循环

// 查询主节点 List<BmsMenuVO> bmsMenuVOList = bmsRoleMenuDao.getAllRoleMenuList(condition);  // 拼装结果  List<BmsMenuVO> bmsMenuTree = new ArrayList<>();  for (BmsMenuVO bmsMenuVO : bmsMenuVOList) {       // 根节点的父Id为null       if (bmsMenuVO.getParentId() == null) {                 bmsMenuTree.add(bmsMenuVO);       }       for (BmsMenuVO menuVO : bmsMenuVOList) {            if (menuVO.getParentId() != null && menuVO.getParentId().equals(bmsMenuVO.getId())) {                if (CollectionUtils.isEmpty(bmsMenuVO.getChildBmsMenuList())) {                         bmsMenuVO.setChildBmsMenuList(new ArrayList<>());                 }                 bmsMenuVO.getChildBmsMenuList().add(menuVO);            }        }   }    // 返回结果  return Result.createWithModels(null, bmsMenuTree); 

（3）map遍历

 // 查询所有节点  List<BmsMenuVO> bmsMenuVOList = bmsRoleMenuDao.getAllRoleMenuList(condition);          // 拼装结果       List<BmsMenuVO> bmsMenuTree = new ArrayList<>();  // 用来存储节点的子元素map  Map<Long, BmsMenuVO> childBmsMenuMap = new LinkedHashMap<>();         for (BmsMenuVO menuVO : bmsMenuVOList) {             childBmsMenuMap.put(menuVO.getId(), menuVO);         }         for (Long bmsMenuId : childBmsMenuMap.keySet()) {             BmsMenuVO menuVO = childBmsMenuMap.get(bmsMenuId);             Long parentId = menuVO.getParentId();             if (parentId == null) {                 bmsMenuTree.add(menuVO);             } else {                 BmsMenuVO parentMenuVO = childBmsMenuMap.get(parentId);                 if (parentMenuVO.getChildBmsMenuList() == null) {                     parentMenuVO.setChildBmsMenuList(new ArrayList<>());                 }                 parentMenuVO.getChildBmsMenuList().add(menuVO);           } }  

2、使用递归查询某个节点所在的树结构

使用场景：当我们得到一个树形结构数据时，可能需要在树形结构上对数据进行筛选，例如通过文件夹（文件）名称模糊查询相关的文件夹并展现其父级。

缺点：需要查询出完整的树形结构才能用作筛选，在数据量非常庞大的时候并不适用。

@Data public class TreeDto {     private String id;    private String name;    private List<TreeDto> subsetTreeDtoList;       public TreeDto(String id,String name,List<TreeDto> subsetTreeDtoList){        this.id = id;        this.name = name;        this.subsetTreeDtoList = subsetTreeDtoList;    } } 

筛选

  /**     * 树形筛选查找     * @param treeDtoList 树形集合     * @param idList 筛选条件(可以是其他条件)     * @return 包含的节点数据     */    public static List<TreeDto> screenTree(List<TreeDto> treeDtoList, List<String> idList){        //最后返回的筛选完成的集合        List<TreeDto> screeningOfCompleteList = new ArrayList<>();        if (listIsNotEmpty(treeDtoList) && listIsNotEmpty(idList)){            for (TreeDto treeDto : treeDtoList){                List<TreeDto> subsetList = treeDto.getSubsetTreeDtoList();                //递归筛选完成后的返回的需要添加的数据                TreeDto addTreeDto = getSubsetPmsPlanPo(treeDto,subsetList,idList);                if (isNotEmpty(addTreeDto)){                    screeningOfCompleteList.add(addTreeDto);                }            }            return screeningOfCompleteList;        }        return null;    }      /**     * 筛选符合的集合并返回     * @param treeDto 树形类     * @param subsetTreeDtoList 子集集合     * @param idList 筛选条件     * @return 筛选成功的类     */    public static TreeDto getSubsetPmsPlanPo(TreeDto treeDto,List<TreeDto> subsetTreeDtoList,List<String> idList){        //作为筛选条件的判断值        String id = treeDto.getId();        //有子集时继续向下寻找        if (listIsNotEmpty(subsetTreeDtoList)){            List<TreeDto> addTreeDtoList = new ArrayList<>();            for (TreeDto subsetTreeDto : subsetTreeDtoList){                List<TreeDto> subsetList = subsetTreeDto.getSubsetTreeDtoList();                TreeDto newTreeDto = getSubsetPmsPlanPo(subsetTreeDto,subsetList,idList);                //当子集筛选完不为空时添加                if (isNotEmpty(newTreeDto)){                    addTreeDtoList.add(newTreeDto);                }            }            //子集满足条件筛选时集合不为空时，替换对象集合内容并返回当前对象            if (listIsNotEmpty(addTreeDtoList)){                treeDto.setSubsetTreeDtoList(addTreeDtoList);                return treeDto;                //当前对象子集对象不满足条件时，判断当前对象自己是否满足筛选条件，满足设置子集集合为空，并返回当前对象            }else if (listIsEmpty(addTreeDtoList) && idList.contains(id)){                treeDto.setSubsetTreeDtoList(null);                return treeDto;            }else {                //未满足筛选条件直接返回null                return null;            }        }else {            //无子集时判断当前对象是否满足筛选条件            if (idList.contains(id)){                return treeDto;            }else {                return null;            }        }    }     /**     * 判断集合为空     * @param list 需要判断的集合     * @return 集合为空时返回 true     */    public static boolean listIsEmpty(Collection list){        return  (null == list || list.size() == 0);    }     /**     * 判断集合非空     * @param list 需要判断的集合     * @return 集合非空时返回 true     */    public static boolean listIsNotEmpty(Collection list){        return !listIsEmpty(list);    }     /**     * 判断对象为null或空时     * @param object 对象     * @return 对象为空或null时返回 true     */    public static boolean isEmpty(Object object) {        if (object == null) {            return (true);        }        if ("".equals(object)) {            return (true);        }        if ("null".equals(object)) {            return (true);        }        return (false);    }     /**     * 判断对象非空     * @param object 对象     * @return 对象为非空时返回 true     */    public static boolean isNotEmpty(Object object) {        if (object != null && !object.equals("") && !object.equals("null")) {            return (true);        }        return (false);    }     public static void main(String[] args) {        TreeDto treeDto1 = new TreeDto("1","A",new ArrayList<TreeDto>());        TreeDto treeDto1_1 = new TreeDto("1.1","A-A",new ArrayList<TreeDto>());        TreeDto treeDto1_2 = new TreeDto("1.2","A-B",new ArrayList<TreeDto>());        TreeDto treeDto1_3 = new TreeDto("1.3","A-C",new ArrayList<TreeDto>());        treeDto1.getSubsetTreeDtoList().add(treeDto1_1);        treeDto1.getSubsetTreeDtoList().add(treeDto1_2);        treeDto1.getSubsetTreeDtoList().add(treeDto1_3);         TreeDto treeDto2 = new TreeDto("2","B",new ArrayList<TreeDto>());        TreeDto treeDto2_1 = new TreeDto("2.1","B-A",new ArrayList<TreeDto>());        TreeDto treeDto2_2 = new TreeDto("2.2","B-B",new ArrayList<TreeDto>());        TreeDto treeDto2_3 = new TreeDto("2.3","B-C",new ArrayList<TreeDto>());        TreeDto treeDto2_3_1 = new TreeDto("2.3.1","B-C-A",null);        treeDto2.getSubsetTreeDtoList().add(treeDto2_1);        treeDto2.getSubsetTreeDtoList().add(treeDto2_2);        treeDto2.getSubsetTreeDtoList().add(treeDto2_3);        treeDto2.getSubsetTreeDtoList().get(2).getSubsetTreeDtoList().add(treeDto2_3_1);         String[] array = {"1.3","2.2","2.3.1"};        List<String> idList = Arrays.asList(array);        List<TreeDto> treeDtoList = new ArrayList<>();        treeDtoList.add(treeDto1);        treeDtoList.add(treeDto2);        System.out.println(JSON.toJSONString(screenTree(treeDtoList,idList)));    } } 

返回结果为