Use abstract class for instance variable in Spring
My problem is I have a Spring model
@Entity
public class PetOwner {
@ManyToOne
@JoinColumn(name = "pet_id", nullable = true)
private Pet pet;
when Pet is an abstract class with two subclasses Dog and Cat.
@Entity
@Inheritance(strategy= InheritanceType.JOINED)
public abstract class Pet {
@OneToMany(fetch = FetchType.LAZY)
protected Set<PetOwner> owners;
}
@Entity
public class Cat extends Pet
@Entity
public class Dog extends Pet
When I create a new PetOwner in Struts form and try to bind its pet to a Dog or Cat object, I get an error:
Error creating bean with name 'de.model.Pet': Instantiation of bean failed;
nested exception is org.springframework.beans.BeanInstantiationException:
Could not instantiate bean class [de.model.Pet]: Is it an abstract class?;
nested exception is java.lang.InstantiationException
How can I tell Spring to initialize de.model.Dog or de.model.Cat based on the class of the pet object?
FYI: I have PetDAO and PetService, but I'm not sure if they affect this problem.
I appreciate any help!
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Personally, I would convert Pet
to Interface
and do Cat
and Dog
implement it to avoid problems like this. Sorry for the off-topic!
Anyway, if you want any member of your class to be dynamically initialized / populated then try the lookup method lookup. Read p. 3.3.4.1 here .
If a class containing a dynamic element was created in scope = singleletone (default for a spring bean container) every time you access a field that has a lookup method, you will get the corresponding object according to your business logic. implemented inside the search method.
Also, I found this example in the spring documentation - I think it is very clear. Take a look at "3.4.6.1 Finding Injection Method"
When setting up a class, PetOwner
assign a lookup method to its member Pet
- it will be called whenever you need a new Pet bean instance.
Good luck!
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