无法在 ModelMapper 中实例化目标 [AbstractClass] 错误的实例

Posted 2023-02-22

【中文标题】无法在 ModelMapper 中实例化目标 [AbstractClass] 错误的实例

【英文标题】：Failed to instantiate instance of destination [AbstractClass] error in ModelMapper

【发布时间】：2022-01-23 00:08:09

【问题描述】：

我有抽象类Room:

@Entity
@DiscriminatorColumn(name = "room_type")
@Data
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class Room 
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "room_id", nullable = false, unique = true)
private int roomId;

@Column(name = "name", nullable = false, length = 255)
private String name;

@JsonIgnore
@OneToMany(mappedBy = "room")
private List<Workstation> workstationsList;

我还有一些从Room 扩展的具体类。 在我的Workstation 类中，我与Room 有One to one 关系：

@Entity
@Data
public class Workstation 
@Id
@Column(name = "workstation_id", nullable = false, unique = true)
private int workstationId;

@ManyToOne
@JoinColumn(name = "room_id")
private Room room;

我正在使用ModelMaper 将WorkstationDTO 映射到Workstation 实体，但我得到Failed to instantiate instance of destination com.entity.Room. Ensure that com.entity.Room has a non-private no-argument constructor. 这可能是因为Room 是抽象类，有没有办法在不删除@ 中的抽象关键字的情况下解决这个问题987654333@实体？

【参考方案1】：

是的。这是因为不能实例化抽象类（也不能实例化接口）。您可以使用转换器，但要实例化一个具体类，您需要知道它的实际类型是什么：

var roomConverter = new Converter<RoomDto, Room>() 
    // inner mapper to avoid any side effects
    private final ModelMapper innerMapper = new ModelMapper();

    @Override
    public Room convert(MappingContext<RoomDto, Room> context) 
        // If your RoomDto had the type as field you could determine the actual type to
        // instantiate, so one of the possible many RoomImpl.
        return innerMapper.map(context.getSource(), RoomImpl.class);
    
;

// Create the type map and register converter
modelMapper.createTypeMap(RoomDto.class, Room.class).setConverter(roomConverter);

现在添加字段，例如：

@Getter
private Class<Room> classOfRoom;

它可以在方法convert(..)中使用来实例化正确的实现。