阅读继承的Json

Question

我正在尝试用Java读取Json文件。但是我不知道如何将包含Java文件的数据分配给子类。我有一个超类，然后有三个子类，这取决于我是否必须填充所提供的数据，并且我不知道如何根据所提供文件的数据来填充这三个子类（扩展了超类）。

Answer 1

这里是如何实现此示例的示例。但是请记住，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 
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
}

汽车子类别

@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的包装器类，应该与您的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
    }

}
}

并且您的示例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

}]