1、创建实体对象

public class TreeNode {
    private String id;
    private String pid;
    private String name;

    private List<TreeNode> children;


    public TreeNode(String id,String pid,String name){
        this.id = id;
        this.pid = pid;
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getPid() {
        return pid;
    }

    public void setPid(String pid) {
        this.pid = pid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }



    public List<TreeNode> getChildren() {
        return children;
    }

    public void setChildren(List<TreeNode> children) {
        this.children = children;
    }

}

2、创建集合转换树工具类

public class TreeVo {
    private List<TreeNode> listJXKHTreeNode=new ArrayList<TreeNode>();
    private List<TreeNode> lstRootJXKHTreeNode=new ArrayList<TreeNode>();
    private int iMaxLevel=1;

    public List<TreeNode> getListJXKHTreeNode() {
        return listJXKHTreeNode;
    }

    public void setListJXKHTreeNode(List<TreeNode> listJXKHTreeNode) {
        this.listJXKHTreeNode = listJXKHTreeNode;
    }

    public List<TreeNode> getLstRootJXKHTreeNode() {
        return lstRootJXKHTreeNode;
    }

    public void setLstRootJXKHTreeNode(List<TreeNode> lstRootJXKHTreeNode) {
        this.lstRootJXKHTreeNode = lstRootJXKHTreeNode;
    }

    public int getiMaxLevel() {
        return iMaxLevel;
    }

    public void setiMaxLevel(int iMaxLevel) {
        this.iMaxLevel = iMaxLevel;
    }



    public static List<TreeNode> listGetStree(List<TreeNode> list) {
        List<TreeNode> treeList = new ArrayList<TreeNode>();
        for (TreeNode tree : list) {
            //找到根
            if (tree.getPid() == null) {
                treeList.add(tree);
            }
            //找到子
            for (TreeNode treeNode : list) {
                if(treeNode.getPid()!=null){
                    if (treeNode.getPid().equals(tree.getId())) {
                        if (tree.getChildren() == null) {
                            tree.setChildren(new ArrayList<TreeNode>());
                        }
                        tree.getChildren().add(treeNode);
                    }
                }

            }
        }
        return treeList;
    }

    //将list转换为树
    public  List<TreeNode> MakeTreeByList(List<TreeNode> listData ){
        if(listData != null) {
            for(int i=0;i<listData.size();i++){

                TreeNode mapObject = listData.get(i);
                String strAPID = mapObject.getPid() == null ? "" : mapObject.getPid();
                Boolean IsHaveParent=false;
                //找根节点
                for(int j=0;j<listData.size();j++){
                    TreeNode mapObjectB=listData.get(j);
                    String strBID=mapObjectB.getId();
                    if(strAPID.equals(strBID)){
                        IsHaveParent=true;
                        break;
                    }
                }
                //如果没有父级节点则为根节点
                if(!IsHaveParent){
                    lstRootJXKHTreeNode.add(mapObject);
                }

            }
        }

        //找上下级关系
        for(int i=0;i<listData.size();i++){

            for(int j=0;j<listData.size();j++){

                if(listData.get(i).getId().equals(listData.get(j).getPid())){
                    if(listData.get(i).getChildren()==null){
                        listData.get(i).setChildren(new ArrayList<TreeNode>());
                    }
                    listData.get(i).getChildren().add(listData.get(j));

                }

            }

        }

        return lstRootJXKHTreeNode;

    }
}

3、测试实例

public class TestListToTree {
    public static void main(String[] args) {
        List<TreeNode> treeNodeList = new ArrayList<>();
        treeNodeList.add(new TreeNode("1","0","人力资源部"));
        treeNodeList.add(new TreeNode("12","1","人一"));
        treeNodeList.add(new TreeNode("12","1","人二"));
        treeNodeList.add(new TreeNode("14","1","人三"));
        treeNodeList.add(new TreeNode("11","1","人四"));
        treeNodeList.add(new TreeNode("2","0","财务资源部"));
        treeNodeList.add(new TreeNode("21","2","财一"));
        treeNodeList.add(new TreeNode("22","2","财二"));
        treeNodeList.add(new TreeNode("23","2","财三"));
        TreeVo treeVo = new TreeVo();
        List<TreeNode> treeNodes = treeVo.MakeTreeByList(treeNodeList);
        for (TreeNode treeNode : treeNodes) {
            System.out.println(treeNode.getName());
        }
    }
}

运行结果：