ClassCastExceptionbeing thrown, this was due to the fact that a lazily loaded List of objects retrieved by hibernate contained proxied objects. The entities that were proxied were using a single table inheritance strategy, so there is a base class that is subclassed several times. The entities once loaded were being sorted into separate lists that are typed according to the subclasses, they were being cast into the appropriate subclass but this cast was failing because instead of being an instance of say
Animalit was an instance of
Animal$$EnhancerByCGLIB$$10db1483i.e. A Hibernate Proxy. Let me show you an example.
Animalclass, lets say,
animal_type_id, which I have defined 2 to be
Dogand 1 to be
Cat. So now we should make sure we have some data in a database table called animals...
assertEqualsat the end of the test pass, even though the code looks like it should be adding items to these lists based on what is in the Adatabase. This is because animal is not an
Hibernate.initialize(animal);which will force the animal class to become the actual object, not the proxy. I felt this approach to be dirty and it is really polluting code that shouldn't really know anything about hibernate.
Animalclass to implement...
Animalclass I showed earlier implement the
instanceofor having to cast anything (which is what was happening in the live code I talked about) which can cause weird side effects and
AnimalEntityVisitor, so when
animal.accept(this);is called, it calls the appropriate visit method on "this". In our case the visit method is just adding the object to a list. So I've updated the
assertEqualscalls to be what I now expect and the test passes.
Labels: ClassCastException, EnhancerByCGLIB, hibernate, java, patterns, spring