java树结构实现方法

1.双层for循环

  List<Map<String, Object>> result = newsflDao.fltree(userid);
        List<Map<String, Object>> listvalue = new ArrayList<>();
        List<Map<String, Object>> nodes;
        for (Map<String, Object> stringObjectMap : result) {
            nodes = new ArrayList<>();
            for (Map<String, Object> objectMap : result) {
                //给每个分类后面添加是否关注，默认为未关注
                if(!stringObjectMap.containsKey("is_gz")){
                    stringObjectMap.put("is_gz",0);
                }
                //把子类放进nodes中
                if (stringObjectMap.get("code").equals(objectMap.get("parent_code"))) {
                    nodes.add(objectMap);
                }
            }
            if (nodes.size() > 0) {
                stringObjectMap.put("nodes", nodes);
                listvalue.add(stringObjectMap);
            }
        }

2.递归