Persistent Cookie Store
First is error handling. The problem is I cannot throw the errors further up in the app as the cookiestore interface doesn't not allow it. 


You can define a custom unchecked exception and throw that.  (Or throw an existing unchecked exception if you can find one that is suitable.)


  Secondly I have made a persistantcookie so I have a concrete class to serialise. I then convert that to the cookie interface. It seems an ugly way to do it.


I don't think you have any sensible alternatives.  (And besides, I disagree that it is "ugly".)



And please correct the spelling of (at least) the public class and method names.  It is like chalk screeching on a blackboard ...