树形结构List转tree（泛型版+普通版）非递归

  public static List listToTreeList(List treeList) {
        if(CollectionUtils.isEmpty(treeList)){
            return treeList;
        }
        Map> treeLevelMap = new HashMap<>();
        Map> treeParentCodeMap = new HashMap<>();
        treeList.stream().forEach(x -> {
            //按照树等级分组
            listGroupByGetFun(treeLevelMap,x,x.getLevel());
            //按照父编码分组
            listGroupByGetFun(treeParentCodeMap,x,x.getParentCode());

        });
        List rootTree = new ArrayList<>();
        //获取树的最大层级
        Integer maxLevel = treeLevelMap.entrySet().stream().map(x -> 
          x.getKey()).max(Integer::compareTo).get();
        int i = 1;
        //循环level
        while (i <= maxLevel) {
            List currentTreeList = treeLevelMap.get(i);
            currentTreeList.stream().forEach(x -> {
                //设置子集合相当于 x.setChild（list）；
                //把当前节点的子集合从treeParentCodeMap中取出通过setChild方法赋值。
                ArrayList childList = (ArrayList) 
                treeParentCodeMap.get(x.getCode());
                x.setChild(childList);
            });
            if (i == 1) {
                rootTree.addAll(currentTreeList);
            }
            i++;
        }
        return rootTree;
    }
    private static  void listGroupByGetFun(Map> map,TreeObj obj,K key) {
        //分组方法（存储分组map,被分组对象）
        //分组属性
        if (key == null) {
            return;
        }
        if (!map.containsKey(key)) {
            map.put(key, new ArrayList<>());
        }
        map.get(key).add(obj);
    }

普通版本

 private static final int LEVEL_INDEX =0;
    private static final int CODE_INDEX =1;
    private static final int PARENT_CODE_INDEX =2;
    private static final int CHILD_LIST_INDEX =3;
    private static Method[] methods;

    public static List listToTreeList(List treeList) {
        if(CollectionUtils.isEmpty(treeList)){
            return treeList;
        }
        Class cls = (Class) treeList.get(0).getClass();
        TreeAnnotations annotation = cls.getAnnotation(TreeAnnotations.class);
        if(null == annotation){
            return treeList;
        }
        TreeUtils.methods = getMethod(cls);
        Map> treeLevelMap = new HashMap<>();
        Map> treeParentCodeMap = new HashMap<>();
        treeList.stream().forEach(x -> {
            //按照树等级分组
            listGroupByGetFun(treeLevelMap, x, getLevel(x));
            //按照父编码分组
            listGroupByGetFun(treeParentCodeMap,x, getParentCode(x));

        });
        List rootTree = new ArrayList<>();
        //获取最大层级数
        Integer maxLevel = treeLevelMap.entrySet().stream().map(x -> x.getKey()).max(Integer::compareTo).get();
        int i = 1;
        //循环level
        while (i <= maxLevel) {
            List currentTreeList = treeLevelMap.get(i);
            currentTreeList.stream().forEach(x -> {
                //设置子集合相当于 x.setChild（list）；
                //把当前节点的子集合从treeParentCodeMap中取出通过setChild方法赋值。
                List childList = treeParentCodeMap.get(getCode(x));
                setChild(x,childList);
            });
            if (i == 1) {
                rootTree.addAll(currentTreeList);
            }
            i++;
        }
        return rootTree;
    }

    //这里为了可读性特意提取出来，后期可自行去留
    private static  Integer getLevel(T x){
        return (Integer) getMethod(methods,x,LEVEL_INDEX);
    }
    private static  String getParentCode(T x){
        return (String)getMethod(methods,x,PARENT_CODE_INDEX);
    }
    private static  String getCode(T x){
        return (String)getMethod(methods,x,CODE_INDEX);
    }
    private static  void setChild(T x,List childList){
        setMethod(methods,x,CHILD_LIST_INDEX,childList);
    }

    private static  void listGroupByGetFun(Map> map,T obj,K key) {
        //分组方法（存储分组map,被分组对象）
        //分组属性
        if (key == null) {
            return;
        }
        if (!map.containsKey(key)) {
            map.put(key, new ArrayList<>());
        }
        map.get(key).add(obj);
    }

    private static void setMethod(Method[] methods,T t,int index,Object setValue){
        try {
            methods[index].invoke(t,setValue);
        } catch (IllegalAccessException | InvocationTargetException e) {
            e.printStackTrace();
        }
    }
    private static Object getMethod(Method[] methods,T t,int index){
        try {
            return methods[index].invoke(t);
        } catch (IllegalAccessException | InvocationTargetException e) {
            e.printStackTrace();
        }
        return null;
    }
    private static Method[] getMethod(Class cls){
        Method[] methods = new Method[4];
        for(Field field:cls.getDeclaredFields()) {
            try {
                PropertyDescriptor pd = new PropertyDescriptor(field.getName(),cls);
                if(field.isAnnotationPresent(LevelAnnotation.class)){
                    methods[LEVEL_INDEX] = pd.getReadMethod();
                }
                if(field.isAnnotationPresent(CodeAnnotation.class)){
                    methods[CODE_INDEX]= pd.getReadMethod();
                }
                if(field.isAnnotationPresent(ParentCodeAnnotation.class)){
                    methods[PARENT_CODE_INDEX]= pd.getReadMethod();
                }
                if(field.isAnnotationPresent(ChildListAnnotation.class)){
                    methods[CHILD_LIST_INDEX] = pd.getWriteMethod();
                }
            } catch (IntrospectionException e) {
                e.printStackTrace();
            }
        }
        return methods;
    }

泛型通用版本，这个可读性差点，可以先看普通版本再看这个泛型版本。

@Data
@TreeAnnotations()
public class TreeObj {
    private String name;
    @LevelAnnotation
    private Integer level;
    @CodeAnnotation
    private String code;
    @ParentCodeAnnotation
    private String parentCode;
    @ChildListAnnotation
    private ArrayList child;

    @Override
    public String toString() {
        return "TreeTest{" +
                "name='" + name + '\'' +
                ", level=" + level +
                ", code='" + code + '\'' +
                ", parentCode='" + parentCode + '\'' +
                '}';
    }
}

测试树对象

 注解类就是名字不一样，其他都一样。注解的作用是标识出哪些字段是层级、哪些字段是code。

可以自己根据实际情况变更。