Pid和id在同一张数据库表中，遍历获取树节点

执行结果

定义keyvalue对象

// keyvalue对象
@Data
public class keyvalue {
    
    

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

    public String pid;
    public String id;
}

定义tree结构对象

@Data
public class ProjectTree {
    
    
    private String id;

    private String name;

    private String childrenId;

    private List<ProjectTree> children;
}

模拟数据

      public List<keyvalue> keyvalueList()
    {
    
    
        List<keyvalue> keyvalues = new ArrayList<>();
        keyvalues.add(new keyvalue("", "1001596232348864541"));//top 顶级菜单
        keyvalues.add(new keyvalue("", "1001596232348864542"));//top 顶级菜单
        keyvalues.add(new keyvalue("", "1001596232348864543"));//top 顶级菜单

        keyvalues.add(new keyvalue("1001596232348864513", "1001596232348864521"));//1
        keyvalues.add(new keyvalue("1001596232348864514", "1001596232348864522"));//2
        keyvalues.add(new keyvalue("1001596232348864515", "1001596232348864533"));//3
        keyvalues.add(new keyvalue("1001596232348864516", "1001596232348864534"));//4
        keyvalues.add(new keyvalue("1001596232348864517", "1001596232348864535"));//5

        keyvalues.add(new keyvalue("1001596232348864518", "1001596232348864513"));//6
        keyvalues.add(new keyvalue("1001596232348864519", "1001596232348864514"));//7
        keyvalues.add(new keyvalue("1001596232348864520", "1001596232348864515"));//8

        keyvalues.add(new keyvalue("1001596232348864521", "1001596232348864536"));//9
        keyvalues.add(new keyvalue("1001596232348864522", "1001596232348864537"));//10
        keyvalues.add(new keyvalue("1001596232348864533", "1001596232348864538"));//11
        keyvalues.add(new keyvalue("1001596232348864534", "1001596232348864539"));//12
        keyvalues.add(new keyvalue("1001596232348864535", "1001596232348864540"));//13

        keyvalues.add(new keyvalue("1001596232348864536", "1001596232348864546"));//14
        keyvalues.add(new keyvalue("1001596232348864537", "1001596232348864547"));//15
        keyvalues.add(new keyvalue("1001596232348864538", "1001596232348864548"));//16
        keyvalues.add(new keyvalue("1001596232348864539", "1001596232348864549"));//17
        keyvalues.add(new keyvalue("1001596232348864540", "1001596232348864550"));//18

        keyvalues.add(new keyvalue("1001596232348864541", "1001596232348864518"));//19
        keyvalues.add(new keyvalue("1001596232348864542", "1001596232348864519"));//20
        keyvalues.add(new keyvalue("1001596232348864543", "1001596232348864520"));//21

        return keyvalues;
    }

遍历首级菜单

   
   private static List<ProjectTree> getTree(List<ProjectTree> rootList, List<ProjectTree> bodyList) {
    
    
        if (bodyList != null && !bodyList.isEmpty()) {
    
    
            //声明一个map，用来过滤已操作过的数据
            Map<String, String> map = new Hashtable<>(bodyList.size());
            rootList.forEach(rootTree -> getChild(rootTree, map, bodyList));
            return rootList;
        } else if (rootList != null) {
    
    
            //当数据只有父节点
            return rootList;
        }
        return null;
    }

遍历子对象

    private static void getChild(ProjectTree treeDto, Map<String, String> map, List<ProjectTree> bodyList) {
    
    
        List<ProjectTree> childList = new ArrayList();
        bodyList.stream()
                .filter(c -> !map.containsKey(c.getId()))
                .filter(c -> c.getChildrenId().equals(treeDto.getId()))
                .forEach(c -> {
    
    
                    map.put(c.getId(), c.getChildrenId());
                    getChild(c, map, bodyList);
                    childList.add(c);
                });
        treeDto.setChildren(childList);//子数据集
    }

启动

   
    public static List<ProjectTree> startTest() {
    
    
        List<ProjectTree> rootList = new ArrayList<>(); //根节点对象存放到这里
        List<ProjectTree> bodyList = new ArrayList<>(); //其他节点存放到这里，可以包含根节点
        for (keyvalue keyvalue : keyvalueList()) {
    
    
            if (keyvalue.getPid().isEmpty()) {
    
    
                ProjectTree pj = new ProjectTree();
                pj.setId(keyvalue.id);
                pj.setName("一级目录");
                pj.setChildrenId("");
                rootList.add(pj);
            } else {
    
    
                ProjectTree pj = new ProjectTree();
                pj.setId(keyvalue.id);
                pj.setName("子集目录");
                pj.setChildrenId(keyvalue.pid);
                bodyList.add(pj);
            }
        }
        List<ProjectTree> stc = getTree(rootList, bodyList);//组装的树返给前端
        return stc;
    }