Java: watching directory for changes

https://docs.oracle.com/javase/tutorial/essential/io/notification.html

see also

• Java: WatchService gets informed before content is copied
• Java 7 WatchService - Ignoring multiple occurrences of the same event
• Java NIO watch Service created both 'ENTRY_CREATE' and 'ENTRY_MODIFY' when a new File is added to the watch folder
• Can I watch for single file change with WatchService (not the whole directory)?