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)); }