java - When and why JPA entities should implement the Serializable interface?

Question

The question is in the title. Below I just described some of my thoughts and findings.

When I had a very simple domain model (3 tables without any relations), all my entities did NOT implement the Serializable interface.

But when the domain model became more complex, I got a RuntimeException, saying that one of my entities didn't implement Serializable.

I use Hibernate as a JPA implementation, and I wonder:

1. Is it a vendor-specific requirement/behavior?
2. What happens with my serializable entities? Should they be serializable for storing or for transferring?
3. At which moment it becomes necessary to make my entity serializable?

Answer 1

According to JPA Spec:

If an entity instance is to be passed by value as a detached object (e.g., through a remote interface), the entity class must implement the Serializable interface.

"JSR 220: Enterprise JavaBeansTM,Version 3.0 Java Persistence API Version 3.0, Final Release May 2, 2006"