使用LinkedList效率更高

 1、单个顶级节点

public static List<CmsStudentOutline> getTreeList(CmsStudentOutline root) {List<CmsStudentOutline> list = new ArrayList<>();Queue<CmsStudentOutline> queue = new LinkedList<>();if (root == null) {return null;}root.setPid("0");//使用UUID也可以 root.setId(UUID.randomUUID().toString());root.setId(IdUtils.simpleUUID());queue.offer(root);//添加一个元素并返回true如果队列已满，则返回falsewhile (!queue.isEmpty()) {CmsStudentOutline tree = queue.poll();//移除并返问队列头部的元素,如果队列为空，则返回nullString pid = tree.getId();List<CmsStudentOutline> children = tree.getChildren();if (children != null) {for (CmsStudentOutline child : children) {child.setPid(pid);//使用UUID也可以 child.setId(UUID.randomUUID().toString());child.setId(IdUtils.simpleUUID());queue.offer(child);//添加一个元素并返回true,如果队列已满，则返回false}}CmsStudentOutline cmsStudentOutline = new CmsStudentOutline();cmsStudentOutline.setId(tree.getId());cmsStudentOutline.setPid(tree.getPid());cmsStudentOutline.setName(tree.getName());list.add(cmsStudentOutline);}return list;}

2、如果有多个顶级节点（循环即可）

public List<CmsStudentOutline> getList(List<CmsStudentOutline> cmsStudentOutline){List<CmsStudentOutline> list = new ArrayList<>();for (CmsStudentOutline studentOutline : cmsStudentOutline) {list.addAll(breadthFirstTree2List(studentOutline));}return list;}