Event driven APIs such as POIFS's and HSSF's need error handling capability.  
Currently if an exception occurs in a listener it has no way of notifying the
caller of an error condition.  

I suggest the listener interface should contain a second method called
"getError" or so that returns a true or false.   This should be called once
after each listener call.  This is needed to support heterogeneous environments
where POI may be used to handle data that may not be valid.