将 JSON 解析为对象

Question

我有一个User 类定义为：

User.java

package model;

import java.util.List;
import java.util.Map;

public class User {
    private final Map<String, List<String>> accountTransactionsMap;

    public User(final Map<String, List<String>> accountTransactionsMap) {
        this.accountTransactionsMap = accountTransactionsMap;
    }

    public Map<String, List<String>> getAccountTransactionsMap() {
        return accountTransactionsMap;
    }
}

我正在调用返回以下响应的 REST API：

{  
   "username1":{  
      "456":[  

      ],
      "123":[  

      ],
      "789":[  

      ]
   },
   "username2":{  
      "123":[  

      ],
      "456":[  

      ],
      "789":[  

      ]
   },
   "username3":{  
      "789":[  

      ],
      "123":[  

      ],
      "456":[  
         "transaction10",
         "transaction6",
         "transaction9",
         "transaction3"
      ]
   }
}

我希望能够解析响应并将其存储在 User 对象中。

我尝试了以下方法：

Test.java

public class Test {
    public static void main(final String[] args) {
        final String response = "{\"username1\":{\"456\":[],\"123\":[],\"789\":[]},\"username2\":{\"123\":[],\"456\":[],\"789\":[]},\"username3\":{\"789\":[],\"123\":[],\"456\":[\"transaction10\",\"transaction6\",\"transaction9\",\"transaction3\"]}}";
        final Gson gson = new Gson();
        final Type map = new TypeToken<Map<String, User>>(){}.getType();
        final Map<String, User> result = gson.fromJson(response, map);
        System.out.println(result);

        if (result != null) {
            for (final Map.Entry<String, User> entry : result.entrySet()) {
                System.out.println("username: " + entry.getKey());
                final User user = entry.getValue();
                System.out.println("transactions: " + user.getAccountTransactionsMap());
            }
        }
    }
}

这会产生输出：

{username1=model.User@80ec1f8, username2=model.User@1445d7f, username3=model.User@6a396c1e}
username: username1
transactions: null
username: username2
transactions: null
username: username3
transactions: null

我期望输出：

{username1=model.User@80ec1f8, username2=model.User@1445d7f, username3=model.User@6a396c1e}
username: username1
transactions: {123=[],456=[],789=[]}
username: username2
transactions: {123=[],456=[],789=[]}
username: username3
transactions: {123=[],456=["transaction10", "transaction6", "transaction9", "transaction3"],789=[]}

如何将accountId 和transactionIds 列表作为User 类中的变量解析到自己的映射中？

编辑：我想问题真的变成了，如何为我的User 类创建自定义TypeToken？

Answer 1

您需要使用Map<String, Map<String, List<String>>>，而不是User 类：

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

import java.io.File;
import java.io.FileReader;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;

public class GsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        final Gson gson = new Gson();
        final Type map = new TypeToken<Map<String, Map<String, List<String>>>>(){}.getType();
        final Map<String, Map<String, List<String>>> result = gson.fromJson(new FileReader(jsonFile), map);
        System.out.println(result);

        if (result != null) {
            for (final Map.Entry<String, Map<String, List<String>>> entry : result.entrySet()) {
                System.out.println("username: " + entry.getKey());
                final Map<String, List<String>> user = entry.getValue();
                System.out.println("transactions: " + user);
            }
        }
    }
}

上面的代码打印：

{username1={456=[], 123=[], 789=[]}, username2={123=[], 456=[], 789=[]}, username3={789=[], 123=[], 456=[transaction10, transaction6, transaction9, transaction3]}}
username: username1
transactions: {456=[], 123=[], 789=[]}
username: username2
transactions: {123=[], 456=[], 789=[]}
username: username3
transactions: {789=[], 123=[], 456=[transaction10, transaction6, transaction9, transaction3]}

如果确实需要，可以在解析后创建User对象。