@Entity
@Getter
@Setter
public class Entity1 {
    @Id
    String id;

    @OneToOne(fetch = FetchType.LAZY, mappedBy = "entity1")
    protected SubClass1 subClass1;

    @OneToOne(fetch = FetchType.LAZY, mappedBy = "entity1")
    protected SubClass2 subClass2;
}

@Entity
@Getter
@Setter
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public abstract class SuperClass implements Serializable {
    @Id
    public String id;

    @ManyToOne
    protected Entity1 entity1;
}

@Entity
@DiscriminatorValue("1")
public class SubClass1 extends SuperClass {
}

@Entity
@DiscriminatorValue("2")
public class SubClass2 extends SuperClass {
}