java将list转为树形结构的方法

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原始数据如下

[
    {
        "name":"甘肃省",
        "pid":0,
        "id":1
    },
    {
        "name":"天水市",
        "pid":1,
        "id":2
    },
    {
        "name":"秦州区",
        "pid":2,
        "id":3
    },
    {
        "name":"北京市",
        "pid":0,
        "id":4
    },
    {
        "name":"昌平区",
        "pid":4,
        "id":5
    }
]

现需要是使用java将以上数据转为树形结构，转化后下的结构如下

[
    {
        "children":[
            {
                "children":[
                    {
                        "name":"秦州区",
                        "pid":2,
                        "id":3
                    }
                ],
                "name":"天水市",
                "pid":1,
                "id":2
            }
        ],
        "name":"甘肃省",
        "pid":0,
        "id":1
    },
    {
        "children":[
            {
                "name":"昌平区",
                "pid":4,
                "id":5
            }
        ],
        "name":"北京市",
        "pid":0,
        "id":4
    }
]

代码如下

/** * listToTree * <p>方法说明<p> * 将JSONArray数组转为树状结构 * @param arr 需要转化的数据 * @param id 数据唯一的标识键值 * @param pid 父id唯一标识键值 * @param child 子节点键值 * @return JSONArray */public static JSONArray listToTree(JSONArray arr,String id,String pid,String child){   JSONArray r = new JSONArray();   JSONObject hash = new JSONObject();   //将数组转为Object的形式，key为数组中的id   for(int i=0;i<arr.size();i++){      JSONObject json = (JSONObject) arr.get(i);      hash.put(json.getString(id), json);   }   //遍历结果集   for(int j=0;j<arr.size();j++){      //单条记录      JSONObject aVal = (JSONObject) arr.get(j);      //在hash中取出key为单条记录中pid的值      JSONObject hashVP = (JSONObject) hash.get(aVal.get(pid).toString());      //如果记录的pid存在，则说明它有父节点，将她添加到孩子节点的集合中      if(hashVP!=null){         //检查是否有child属性         if(hashVP.get(child)!=null){            JSONArray ch = (JSONArray) hashVP.get(child);            ch.add(aVal);            hashVP.put(child, ch);         }else{            JSONArray ch = new JSONArray();            ch.add(aVal);            hashVP.put(child, ch);         }      }else{         r.add(aVal);      }   }   return r;}
测试代码如下

public static void main(String[] args){   List<Map<String,Object>> data = new ArrayList<>();   Map<String,Object> map = new HashMap<>();   map.put("id",1);   map.put("pid",0);   map.put("name","甘肃省");   data.add(map);   Map<String,Object> map2 = new HashMap<>();   map2.put("id",2);   map2.put("pid",1);   map2.put("name","天水市");   data.add(map2);   Map<String,Object> map3 = new HashMap<>();   map3.put("id",3);   map3.put("pid",2);   map3.put("name","秦州区");   data.add(map3);   Map<String,Object> map4 = new HashMap<>();   map4.put("id",4);   map4.put("pid",0);   map4.put("name","北京市");   data.add(map4);   Map<String,Object> map5 = new HashMap<>();   map5.put("id",5);   map5.put("pid",4);   map5.put("name","昌平区");   data.add(map5);   System.out.println(JSON.toJSONString(data));   JSONArray result = listToTree(JSONArray.parseArray(JSON.toJSONString(data)),"id","pid","children");   System.out.println(JSON.toJSONString(result));}

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