使用继承读取 Json [重复]

Question

我正在尝试用 Java 读取 Json 文件。但我不知道如何将包含 Java 文件的数据分发给子类。 我有一个超类，然后我有三个子类，这取决于提供的数据我必须填写与否，我不知道如何根据提供的数据填充这三个子类（扩展超类）文件。

Answer 1

这是一个示例，说明如何实现这一点。但请记住，要这样做，您需要在 json 中提供类型信息，以便它将使用类型信息将 json 转换为 Java 对象。

@JsonTypeInfo(
  use = JsonTypeInfo.Id.NAME, 
  include = JsonTypeInfo.As.PROPERTY, 
  property = "type")
@JsonSubTypes({ 
  @Type(value = Car.class, name = "car"), 
  @Type(value = Truck.class, name = "truck") 
}) // magic happens here, when we give type information using per-class annotations, this will be used by jackson to convert the json to appropriate java objects.
public abstract class Vehicle {
    private String make;
    private String model;

    protected Vehicle(String make, String model) {
        this.make = make;
        this.model = model;
    }

    // no-arg constructor, getters and setters
}

汽车子类

@JsonIgnoreProperties({ // any properties from parent that can be ignored })
public class Car extends Vehicle {
    // any properties from this class to be ignored place it above the property
    @JsonIgnore
    private int seatingCapacity;
    private double topSpeed;

    public Car(String make, String model, int seatingCapacity, double topSpeed) {
        super(make, model);
        this.seatingCapacity = seatingCapacity;
        this.topSpeed = topSpeed;
    }

    // no-arg constructor, getters and setters
}

卡车子类：

public class Truck extends Vehicle {

    private double payloadCapacity;

    public Truck(String make, String model, double payloadCapacity) {
        super(make, model);
        this.payloadCapacity = payloadCapacity;
    }

    // no-arg constructor, getters and setters
}

用于读取 json 的包装类，应与您的 json 数组键相同。

public class VehicleManager {
    private List<Vehicle> vehicles;

   // setters, getters, no arg constructor
}

主类

public class AppStart {
  public static void main(String[] args) throws FileNotFoundException, IOException {

    VehicleManager vehicleManager = new VehicleManager();
    ObjectMapper objectMapper = new ObjectMapper();
    try{
    objectMapper.readerFor(VehicleManager.class).readValue(new File("yourJsonFilePath"));
    }
    catch(IOException ie){
      // log an IOException or do some other operation like rethrow, etc.,
    }
    catch(Exception e){
      // log exception
    }

}
}

你的示例 json 应该像

"vehicleManager":[{
"type": "car", // type information should be provided here
"make": "Toyota",
"model": "Camry",
"seatingCapacity": 5,
"topSpeed": 168.8

},
{
"type": "car", // type information should be provided here
"make": "Hyundai",
"model": "Elantra",
"seatingCapacity": 5,
"topSpeed": 178.8

}]