Java 8: Lambda-Streams, Filter by Method with Exception

I have a problem trying out the Lambda expressions of Java 8. Usually it works fine, but now I have methods that throw IOException's. It's best if you look at the following code: class Bank{ .... public Set<String> getActiveAccountNumbers() throws IOException { Stream<Account> s = accounts.values().stream(); s = s.filter(a -> a.isActive()); Stream<String> ss = s.map(a -> a.getNumber()); return ss.