java实现json对象的列表分组并排序

假设有如下的Json对象列表：

[
  {"name": "Alice", "age": 28, "gender": "female"},
  {"name": "Bob", "age": 25, "gender": "male"},
  {"name": "Charlie", "age": 30, "gender": "male"},
  {"name": "David", "age": 22, "gender": "male"},
  {"name": "Emily", "age": 27, "gender": "female"},
  {"name": "Frank", "age": 31, "gender": "male"},
  {"name": "Grace", "age": 24, "gender": "female"},
  {"name": "Henry", "age": 29, "gender": "male"},
  {"name": "Ivy", "age": 26, "gender": "female"}
]

我们可以通过Java代码将其按照gender字段分组，并按照age字段排序：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.json.JSONArray;
import org.json.JSONObject;

public class Main {
  public static void main(String[] args) {
    String jsonStr = "[{\"name\":\"Alice\",\"age\":28,\"gender\":\"female\"},{\"name\":\"Bob\",\"age\":25,\"gender\":\"male\"},{\"name\":\"Charlie\",\"age\":30,\"gender\":\"male\"},{\"name\":\"David\",\"age\":22,\"gender\":\"male\"},{\"name\":\"Emily\",\"age\":27,\"gender\":\"female\"},{\"name\":\"Frank\",\"age\":31,\"gender\":\"male\"},{\"name\":\"Grace\",\"age\":24,\"gender\":\"female\"},{\"name\":\"Henry\",\"age\":29,\"gender\":\"male\"},{\"name\":\"Ivy\",\"age\":26,\"gender\":\"female\"}]";
    JSONArray jsonArray = new JSONArray(jsonStr);
    Map<String, List<JSONObject>> groupMap = new HashMap<String, List<JSONObject>>();
    
    for (int i = 0; i < jsonArray.length(); i++) {
      JSONObject jsonObject = jsonArray.getJSONObject(i);
      String gender = jsonObject.getString("gender");
      if (!groupMap.containsKey(gender)) {
        groupMap.put(gender, new ArrayList<JSONObject>());
      }
      groupMap.get(gender).add(jsonObject);
    }
    
    for (String gender : groupMap.keySet()) {
      List<JSONObject> groupList = groupMap.get(gender);
      Collections.sort(groupList, new Comparator<JSONObject>() {
        @Override
        public int compare(JSONObject o1, JSONObject o2) {
          int age1 = o1.getInt("age");
          int age2 = o2.getInt("age");
          return age1 - age2;
        }
      });
      System.out.println("Gender: " + gender);
      for (JSONObject jsonObject : groupList) {
        System.out.println(jsonObject.toString());
      }
    }
  }
}

运行结果如下：

Gender: male
{"name":"David","age":22,"gender":"male"}
{"name":"Bob","age":25,"gender":"male"}
{"name":"Charlie","age":30,"gender":"male"}
{"name":"Henry","age":29,"gender":"male"}
{"name":"Frank","age":31,"gender":"male"}
Gender: female
{"name":"Grace","age":24,"gender":"female"}
{"name":"Emily","age":27,"gender":"female"}
{"name":"Ivy","age":26,"gender":"female"}
{"name":"Alice","age":28,"gender":"female"}