squid:S1860 - Synchronization should not be based on Strings or boxed primitives

[georgekankava]

This pull request is focused on resolving occurrences of Sonar rule
squid:S1860 - Synchronization should not be based on Strings or boxed primitives.
You can find more information about the issue here:
https://dev.eclipse.org/sonar/coding_rules#q=squid%3AS1860
Please let me know if you have any questions.
George Kankava

[tea-dragon]

the change to ValueFilterRandom seems safe enough, but it seems like you have replaced instance level locking with class (static) level locking (maybe that is fine anyway. It isn't a hugely important filter...). However, in FactoryInputStream, there are several calls to eg. key.wait() and key.notifyAll() which are not okay with the removal of the synchronization on them on the key object. see eg.: https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait().

Those are both pretty bizarre classes though. I think i'd end up just gutting most of them myself. As an aside, I generally prefer to go with explicit locks over synchronization blocks. This isn't widely accepted as the best practice or anything, but in my experience, synchronized keywords on methods, blocks, "this", and in static methods tend to lead to all kinds of shenanigans.

Sorry I haven't gotten back to your previous PR yet, but thanks for your continued efforts! :)