Java后台生成树状结构工具类

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TreeUtil {
//    private static String PID = "000000";

    /**
     * 将平行的树，转化为一颗有层级关系的树
     * @param list
     * @param pId
     * @return
     */
    public static List<TreeData> getTreeList(List<TreeData> list,String pId){
        if (list == null){
            return null;
        }
        //获取所有头节点
        List<TreeData> rootNode = new ArrayList<>();
        for (TreeData treeData: list ){
            if (treeData.getId().equals(pId)){
                rootNode.add(treeData);
            }
        }
        //头节点不存在的情况
        if (rootNode.size() == 0){
            return getChild(pId,list);
        }
        //头节点存在的情况
        for (TreeData treeData : rootNode){
            String id = treeData.getId();
            treeData.setChild(getChild(id,list));
        }
        return rootNode;
    }
    private static List<TreeData> getChild(String id,List<TreeData> list){
        //找到id节点子节点
        List<TreeData> childList = new ArrayList<>();
        for (TreeData treeData: list){
            if (treeData.getpId().equals(id)){
               childList.add(treeData);
            }
        }
        //给子节点设置子节点
        for (TreeData treeData : childList){
            id = treeData.getId();
            //递归
            treeData.setChild(getChild(id,list));
        }
        if (childList.size() == 0){
            return null;
        }
        return childList;
    }

    /**
     * 获取指定层级的树
     * @param treeList
     * @param level
     * @return
     */
    public static List<TreeData> getTreeNodeOnLevel(List<TreeData> treeList,int level){
        if (treeList == null && treeList.size() == 0){
            return  new ArrayList<>();
        }
        ArrayList<TreeData> treeListOnLevel = new ArrayList<>();
        //调用递归方法
        treeList = TreeUtil.recursionQueryTree(treeList, treeListOnLevel, 0,level);
        return treeList;
    }

    /**
     * 递归查所有指定层级的树节点
     * @param treeList
     * @param treeListOnLevel
     * @param currentLevel
     * @param level
     * @return
     */
    private static List<TreeData> recursionQueryTree(List<TreeData> treeList,List<TreeData> treeListOnLevel,int currentLevel,int level){
        currentLevel++;
        //递归循环查询指定层级树
        for (TreeData treeData : treeList){
            if (currentLevel == level){
                treeListOnLevel.add(treeData);
                continue;
            }
            //递归
            if (treeData.getChild() == null || treeData.getChild().size() == 0){
                continue;
            }
            recursionQueryTree(treeData.getChild(),treeListOnLevel,currentLevel,level);
        }
        return treeListOnLevel;
    }



    /**
     * 统计一颗树的深度
     * @param treeList
     * @return
     */
    public static int getTreeLevel(List<TreeData> treeList){
        if (treeList == null || treeList.size() == 0){
            return 0;
        }
        //调用递归统计方法
        return TreeUtil.recursionCount(treeList,0,0);
    }

    private static int  recursionCount(List<TreeData> treeList,int currentlevel,int maxlevel){
        currentlevel++;
        //当当前层级大于目前最大层级时覆盖
        if (currentlevel > maxlevel){
            maxlevel = currentlevel;
        }
        //递归遍历节点
        for (TreeData treeData : treeList){
            //如果子节点为空不进行递归
            if (treeData.getChild() == null || treeData.getChild().size() == 0){
                continue;
            }
            //递归
            maxlevel = recursionCount(treeData.getChild(), currentlevel, maxlevel);
        }
        return maxlevel;
    }

    /**
     * 获取指定id在此树中的层级位置
     *
     * @param list 要遍历的树
     * @param id 要寻找的节点Id
     * @param rankCount 层级统计器，传入0即可
     * @return
     */
    public static Map<String,Object> getNode(List<TreeData> list,String  id,Integer rankCount){
        TreeData node = null;
        //计数器加一
        rankCount++;
        Map<String,Object> map = new HashMap<>();
        map.put("node",node);
        map.put("rankCount",rankCount);
        //如果传入的树为0或返回层级0
        if (list == null || list.size() == 0){
            map.put("rankCount",0);
            return map;
        }
        //遍历树
        for (TreeData treeData : list){
            if (treeData.getId().equals(id)){
                map.put("node",treeData);
                return map;
            }
            if (treeData.getChild() == null || treeData.getChild().size() == 0){
                continue;
            }
            //递归
            Map<String,Object> map1 = getNode(treeData.getChild(),id,rankCount);
            if (map1.get("node") != null){
                return  map1;
            }
        }
        //如果传入的节点是不存在的，返回层级0
        map.put("rankCount",0);
       return map;
    }



}

import java.util.List;

public class TreeData {
    private String id;
    private String name;
    private String pId;
    private List<TreeData> child;

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getpId() {
        return pId;
    }

    public void setpId(String pId) {
        this.pId = pId;
    }

    public List<TreeData> getChild() {
        return child;
    }

    public void setChild(List<TreeData> child) {
        this.child = child;
    }

    @Override
    public String toString() {
        return "TreeData{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", pId='" + pId + '\'' +
                ", child=" + child +
                '}';
    }
}