How can I receive Windows filesystem events in Java?

Question

I need to know when a new file appears in a directory. Obviously, I could poll the file system periodically, but that has all the normal downsides of polling mechanisms.

I know that windows supports file system events, and this project is already constrained to the Windows platform by other requirements.

Does anyone have experience receiving Windows filesystem events inside a JVM? If so what are the best practices, patterns, and/or libraries you have used?

A quick google turns up this library. Does anyone have experience with it (or any other) that they'd be willing to share?

possible dup of http://stackoverflow.com/questions/730186/suggestions-sample-code-for-filesystemwatcher-in-java/732418 — notnoop, Jul 21 '09 at 18:59
another possible dup: http://stackoverflow.com/questions/1096404 — dfa, Jul 21 '09 at 19:00
Thanks for the dupe links - I didn't find those with an (apparently too brief) search. I've voted to close, especially for 1096404. — Jared, Jul 22 '09 at 15:42
possible duplicate of [Is there a sophisticated file system monitor for Java which is freeware or open source?](http://stackoverflow.com/questions/1096404/is-there-a-sophisticated-file-system-monitor-for-java-which-is-freeware-or-open-s) — Jared, Jul 09 '11 at 19:30

score 7 · Accepted Answer · edited Jul 29 '12 at 01:24

7

I think this is one of the key features of Java 7 when it is more available. Example code from Sun's blog on Java 7:

import static java.nio.file.StandardWatchEventKind.*;

Path dir = ...;
try {
    WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
} catch (IOException x) {
    System.err.println(x);
}

edited Jul 29 '12 at 01:24

Bill the Lizard

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answered Jul 21 '09 at 18:55

Brian

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If this is for production code Java 7 should not be used. It isn't released. – Alain O'Dea Oct 01 '10 at 12:39

score 2 · Answer 2 · answered Oct 01 '10 at 12:17

2

For Java 6 or older use JNA's com.sun.jna.platform.win32.FileMonitor.

answered Oct 01 '10 at 12:17

dB.

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score 1 · Answer 3 · answered Jul 21 '09 at 18:53

Something quite low level and OS-specific like that is going to need native code (as per the link you mention). That library looks relatively small, so in the worst case you could probably fix any problems if your C++ is good enough.

If you can at all avoid it though, I'd suggest not using native code - library or not. What is so demanding about your scenario that you can't have a background thread poll?

score 1 · Answer 4 · edited May 23 '17 at 12:25

1

Brian Agnew's recommendation of JNotify is a good one: Is there a sophisticated file system monitor for Java which is freeware or open source?

Description from http://jnotify.sourceforge.net/:

JNotify is a java library that allow java application to listen to file system events, such as:

File created

File modified

File renamed

File deleted

edited May 23 '17 at 12:25

Community

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answered Oct 01 '10 at 12:42

Alain O'Dea

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score 1 · Answer 5 · answered Dec 14 '11 at 10:34

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You can use opensource JPollar framework to poll the directory in time intervals. It also allows time based polling.

answered Dec 14 '11 at 10:34

Ritesh

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It would be great if you provide a link to complete the answer – voromax Nov 04 '12 at 11:14

score 0 · Answer 6 · answered Jul 21 '09 at 19:23

0

If not using Jdk7 you'll have to use JNI.

answered Jul 21 '09 at 19:23

John Doe

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How can I receive Windows filesystem events in Java?

6 Answers6