I think you've basically got it but the collection is returning a list of Cat objects that simply implement the base class Object's toString() method. If you override this method on the Cat class and print something more to your liking then you should be good to go.
BTW - this is a Java problem, not necessarily a Spring problem.
Also, if you want your 3 cat instances to have any kind of name when they are printed out, you might want to modify your bean definitions as follows
Or... even better if you add
to the <beans> definition then you can do the following