Java - File Change Notification (WatchService)

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Java - File Change Notification (WatchService)


• Improve performance of applications that are forced to poll the file system today
• WatchService
– Watch registered objects for events and changes
– Makes use of native event facility where available
– Supports concurrent processing of events
• Path implements Watchable
– Register directory to get events when entries are created, deleted, or modified


WatchService API


• WatchKey represents registration of a watchable object with a WatchService.
// register
WatchKey key = file.register(watcher, ENTRY_CREATE, ENTRY_MODIFY);
// cancel registration
key.cancel();

WatchKey represents registration of a watchable object with a WatchService.
• WatchKey signalled and queued when event detected
• WatchService poll or take methods used to retrieve signalled key.

class WatchService {
 WatchKey take();
 WatchKey poll();
 WatchKey poll(long timeout, TimeUnit unit);

WatchKey represents registration of a watchable object with a WatchService.
• WatchKey signalled and queued when event detected
• WatchService poll or take methods used to retrieve signalled keys
• Process events
• WatchKey reset method returns key to ready state

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