我有一個User類定義為：User.javapackage 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;    }}我正在調用返回以下響應的 REST API：{     "username1":{        "456":[        ],      "123":[        ],      "789":[        ]   },   "username2":{        "123":[        ],      "456":[        ],      "789":[        ]   },   "username3":{        "789":[        ],      "123":[        ],      "456":[           "transaction10",         "transaction6",         "transaction9",         "transaction3"      ]   }}我希望能夠解析響應并將其存儲在User對象中。我嘗試了以下方法：Test.javapublic 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());            }        }    }}這會產生輸出：{username1=model.User@80ec1f8, username2=model.User@1445d7f, username3=model.User@6a396c1e}username: username1transactions: nullusername: username2transactions: nullusername: username3transactions: null