Mapstruct双向映射抛出内存不足错误

Question

//Entities and DTOs

public class JourneyType implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "journey_type_id")
    private Long journeyTypeId;

    private String type;

    // bi-directional many-to-one association to JourneyRent
    @OneToMany(mappedBy = "journeyType")
    private Set<JourneyRent> journeyRents;
}

public class JourneyTypeTO implements Serializable {

    private Long journeyTypeId;
    private String type;
    private Set<JourneyRentTO> journeyRents;
}

public class JourneyRent implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "journey_rent_id")
    private Long journeyRentId;

    @Column(name = "min_max_travel_km")
    private Double minMaxTravelKm;

    @Column(name = "rent_charges")
    private BigDecimal rentCharges;

    // bi-directional many-to-one association to JourneyType
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "journey_type_id")
    private JourneyType journeyType;
    
    // bi-directional many-to-one association to VehicleType
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "vehicle_type_id")
    private VehicleType vehicleType;
}

public class JourneyRentTO implements Serializable {

    private Long journeyRentId;
    private Double minMaxTravelKm;
    private BigDecimal rentCharges;
    private JourneyTypeTO journeyType;  
    private VehicleTypeTO vehicleType;
}

public class VehicleType implements Serializable {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="vehicle_type_id")
    private Long vehicleTypeId;

    private String type;

    //bi-directional many-to-one association to JourneyRent
    @OneToMany(mappedBy="vehicleType")
    private Set<JourneyRent> journeyRents;
}

public class VehicleTypeTO implements Serializable {
    private Long vehicleTypeId;
    private String type;
    private Set<JourneyRentTO> journeyRents;
}

// Mapper interfaces
@Mapper(uses = {JourneyRentMapper.class}, unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface JourneyTypeMapper {
    JourneyTypeMapper INSTANCE = Mappers.getMapper(JourneyTypeMapper.class);
    
    @Mapping(target = "journeyBookings", ignore = true)
    JourneyTypeTO toDTO(JourneyType journeyType, @Context CycleAvoidingMappingContext cycleAvoidingMappingContext);

    @Mapping(target = "journeyBookings", ignore = true)
    JourneyType toEntity(JourneyTypeTO journeyType);
}

@Mapper(uses = {JourneyTypeMapper.class, VehicleTypeMapper.class}, unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface JourneyRentMapper { 
    JourneyRentMapper INSTANCE = Mappers.getMapper(JourneyRentMapper.class);

    @Mapping(target = "journeyType", ignore = true)
    JourneyRentTO toDTO(JourneyRent journeyRent, @Context CycleAvoidingMappingContext cycleAvoidingMappingContext);
    
    @Mapping(target = "journeyBookingVehicles", ignore = true)
    JourneyRent toEntity(JourneyRentTO journeyRentTo);
}

@Mapper(unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface VehicleTypeMapper {
    VehicleTypeMapper INSTANCE = Mappers.getMapper(VehicleTypeMapper.class);

    VehicleTypeTO toDTO(VehicleType vehiType);

    VehicleType toEntity(VehicleTypeTO vehiTypeTo);
}

public class CycleAvoidingMappingContext {
    private final Map<Object, Object> knownInstances = new IdentityHashMap<>();

    @BeforeMapping
    public <T> T getMappedInstance(Object source, @TargetType Class<T> targetType) {
        return targetType.cast(knownInstances.get(source));
    }

    @BeforeMapping
    public void storeMappedInstance(Object source, @MappingTarget Object target) {
        knownInstances.put(source, target);
    }
}

There is a bi-directional relationship between JourneyType and JourneyRent. Now JPQL query returns JourneyType Object which has a reference of JourneyRent object and in turn JourneyRent object has a reference of JourneyType Object.

Usage :

List<JourneyTypeTO> journeyTypeTos = new ArrayList<>();
    for (JourneyType journeyType : journeyTypes) {
        journeyTypeTos.add(JourneyTypeMapper.INSTANCE.toDTO(journeyType, new CycleAvoidingMappingContext()));
}

When I try to map Entity to TO, I'm getting out of memory error. How can I map the objects for this scenario ?

Answer 1

I see that you are using the example of the CycleAvoidingMappingContext . The reason why it isn't working to you is because you are not passing it in your VehicleMapper . MapStruct will use the VehicleMapper to map your vehicles and there is no context that would store the cycles.