Is there a helper to know whether a property has been loaded by Hibernate?

According to the documentation for Hibernate 5.4

Hibernate API

boolean personInitialized = Hibernate.isInitialized(person);

boolean personBooksInitialized = Hibernate.isInitialized(person.getBooks());

boolean personNameInitialized = Hibernate.isPropertyInitialized(person, "name");

JPA

In JPA there is an alternative means to check laziness using the following javax.persistence.PersistenceUtil pattern (which is recommended wherever possible).

PersistenceUtil persistenceUnitUtil = Persistence.getPersistenceUtil();

boolean personInitialized = persistenceUnitUtil.isLoaded(person);

boolean personBooksInitialized = persistenceUnitUtil.isLoaded(person.getBooks());

boolean personNameInitialized = persistenceUnitUtil.isLoaded(person, "name");

There are two methods, actually.

To find out whether a lazy property has been initialized you can invoke Hibernate.isPropertyInitialized() method with your entity instance and property name as parameters.

To find out whether a lazy collection (or entity) has been initialized (like in your example) you can invoke Hibernate.isInitialized() with collection (entity) instance as parameter.