Gson RuntimeTypeAdapterFactory在反序列化之后将我的userType转换为空。

Question

我正在使用来自https://github.com/google/gson/blob/master/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java的https://github.com/google/gson/blob/master/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java，并试图从包含以下值的userData.json文件中将json反序列化为用户对象：

[
  {
    "id": "a66c4e96-3370-47e3-a757-d7d9417208db",
    "userType": "ADMIN",
    "firstName": "admin1",
    "lastName": "adminlast1",
    "username": "admin0101",
    "email": "abc1@abc.com",
    "password": "abc123",
    "address": null
  },
  {
    "id": "4948f8c4-7c89-4b7a-92a8-a0ed9daa5b39",
    "userType": "REGULAR",
    "firstName": "regular1",
    "lastName": "regularlast1",
    "username": "regular0101",
    "email": "abc2@abc.com",
    "password": "abc123",
    "address": null
  },
  {
    "id": "9dc587e1-b8e1-441a-a036-44cd091ce405",
    "userType": "OWNER",
    "firstName": "owner1",
    "lastName": "ownerlast1",
    "username": "owner0101",
    "email": "abc3@abc.com",
    "password": "abc123",
    "address": null
  }
]

但是，当我试图从.json文件中读取它们时，userType变成了null，如下所示：

在我的User课上：

public class User {
    private String id;
    protected UserType userType;
    private String firstName;
    private String lastName;
    private String username;
    private String email;
    private String password;
    private String address;

    public User(String id, UserType userType, String firstName, String lastName, String username, String email, String password, String address) {
        this.id = id;
        this.userType = userType;
        this.firstName = firstName;
        this.lastName = lastName;
        this.username = username;
        this.email = email;
        this.password = password;
        this.address = address;
    }
}

在我的Admin中，“所有者”和“常规”类：

public class Admin extends User{
    private String adminDetails;
    public Admin(String id, String firstName, String lastName, String username, String email, String password, String address, String adminDetails) {
        super(id, UserType.ADMIN, firstName, lastName, username, email, password, address);
        this.adminDetails = adminDetails;
    }
}

public class Owner extends User{
    private String ownerDetails;
    public Owner(String id, String firstName, String lastName, String username, String email, String password, String address, String ownerDetails) {
        super(id, UserType.OWNER, firstName, lastName, username, email, password, address);
        this.ownerDetails = ownerDetails;
    }
}

public class Regular extends User{
    private String regularDetails;
    public Regular(String id, String firstName, String lastName, String username, String email, String password, String address, String regularDetails) {
        super(id, UserType.REGULAR, firstName, lastName, username, email, password, address);
        this.regularDetails = regularDetails;
    }
}

我是如何编写从json加载的RuntimeTypeAdapaterFactory和方法的。

 private final Type USER_LIST_TYPE = new TypeToken<ArrayList<User>>(){}.getType();

    //used for deserialization of User
    RuntimeTypeAdapterFactory<User> adapter = RuntimeTypeAdapterFactory.of(User.class, "userType")
            .registerSubtype(Admin.class, UserType.ADMIN.name())
            .registerSubtype(Owner.class, UserType.OWNER.name())
            .registerSubtype(Agent.class, UserType.AGENT.name())
            .registerSubtype(Regular.class, UserType.REGULAR.name())
            .registerSubtype(Pending.class, UserType.PENDING.name());

    //load from json file based on provided UserType
    private ArrayList<User> loadData(UserType userType){
        try {
            fileReader = new FileReader(getPath(loadDataType));
            gson = new GsonBuilder().registerTypeAdapterFactory(adapter).create();
            reader = new JsonReader(fileReader);
            data = gson.fromJson(reader, USER_LIST_TYPE);
            fileReader.close();


        } catch (IOException e) {
            e.printStackTrace();
        }
        if (data == null){
            return new ArrayList<User>();
        }

        return data;
    }

Answer 1

您必须使用RuntimeTypeAdapterFactory.of(Class<T> baseType, String typeFieldName, boolean maintainType)重载并指定maintainType=true。否则，当分配字段值时，Gson将忽略其值。

但是，问题是您的User类是否真的需要一个userType字段。在使用RuntimeTypeAdapterFactory时，Gson不需要这样做。如果您需要应用程序逻辑中的用户类型值，那么让User声明一个抽象的getUserType()方法，然后重写子类(例如，Admin会将其实现为return UserType.ADMIN)也许会更好。使用当前的实现，(理论上) Regular具有用户类型的ADMIN是可能的。