//第一個參數(shù)，需要生成樹的數(shù)組，第二個參數(shù)為樹的根節(jié)點
public JSONObject getJsontree(JSONArray json,JSONObject job){
 JSONArray tempJson = JSONArray.fromObject("[]");
 //篩選出父id等于job里面id的科室
 for(int i = 0;i < json.size();i++) 
 { 
 //這里可以使用Iterator 
 if(json.getJSONObject(i).get("parent_id").equals(job.get("unit_sn"))) {  
  tempJson.add(json.getJSONObject(i));
 }; 
 }
 // 優(yōu)化，減少科室集合的數(shù)量，避免重復查詢，有再優(yōu)化的方法，希望告知。。
 json.removeAll(tempJson);
 for(int i = 0;i < tempJson.size(); i ++) {
 //對第二層進行遞歸，此處類推
 getJsontree(json, tempJson.getJSONObject(i));
 }
 //生成完的樹結構map集合加到根節(jié)點
 if(tempJson.size()!=0)
 job.put("children", tempJson);
 return job; 
}

[
 { text: '節(jié)點1', children: [
  { text: '節(jié)點1.1' },
  { text: '節(jié)點1.2' },
  { text: '節(jié)點1.3', children: [
  { text: '節(jié)點1.3.1' },
  { text: '節(jié)點1.3.2' }
  ]
  },
  { text: '節(jié)點1.4' }
 ]
 }
 ]

[
 {
 "name":"甘肅省",
 "pid":0,
 "id":1
 },
 {
 "name":"天水市",
 "pid":1,
 "id":2
 },
 {
 "name":"秦州區(qū)",
 "pid":2,
 "id":3
 },
 {
 "name":"北京市",
 "pid":0,
 "id":4
 },
 {
 "name":"昌平區(qū)",
 "pid":4,
 "id":5
 }
]

[
 {
 "children":[
  {
  "children":[
   {
   "name":"秦州區(qū)",
   "pid":2,
   "id":3
   }
  ],
  "name":"天水市",
  "pid":1,
  "id":2
  }
 ],
 "name":"甘肅省",
 "pid":0,
 "id":1
 },
 {
 "children":[
  {
  "name":"昌平區(qū)",
  "pid":4,
  "id":5
  }
 ],
 "name":"北京市",
 "pid":0,
 "id":4
 }
]

 import com.alibaba.fastjson.JSON;
 import com.alibaba.fastjson.JSONArray;
 import com.alibaba.fastjson.JSONObject;
 
 public static JSONArray listToTree(JSONArray arr, String id, String pid, String child) {
 JSONArray r = new JSONArray();
 JSONObject hash = new JSONObject();
 //將數(shù)組轉為Object的形式，key為數(shù)組中的id
 for (int i = 0; i < arr.size(); i++) {
  JSONObject json = (JSONObject) arr.get(i);
  hash.put(json.getString(id), json);
 }
 //遍歷結果集
 for (int j = 0; j < arr.size(); j++) {
  //單條記錄
  JSONObject aVal = (JSONObject) arr.get(j);
  //在hash中取出key為單條記錄中pid的值
  String pidStr = "";
  Object pidObj = aVal.get(pid);
  if (aVal.get(pid) != null) {
  pidStr = aVal.get(pid).toString();
  }
  JSONObject hashVP = (JSONObject) hash.get(pidStr);
  //如果記錄的pid存在，則說明它有父節(jié)點，將她添加到孩子節(jié)點的集合中
  if (hashVP != null) {
  //檢查是否有child屬性
  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;
 }

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","甘肅省");
 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","秦州區(qū)");
 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","昌平區(qū)");
 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));
}