java.nio.file.WatchEvent gives me only relative path. How can I get the absolute path of the modified file?

Question

I am using Java 7, java.nio.file.WatchEvent along with the WatchService. After registering, when I poll for ENTRY_MODIFY events, I cannot get to the absolute path of the file for the event. Is there any way to get to the absolute path of the file from WatchEvent object?

score 116 · Accepted Answer · edited Jul 17 '18 at 21:19

116

You need to get the parent directory from the WatchKey to resolve the full path

WatchKey key;
WatchEvent<Path> event;

Path dir = (Path)key.watchable();
Path fullPath = dir.resolve(event.context());

This piece of code reads like it needs accompanying documentation to be grasped, it makes little sense on its own. What were their intentions with this particular API design?

And this is only the beginning of possibly unintuitive usage. Java's file watcher API is subjectively inferior to alternative libraries.

edited Jul 17 '18 at 21:19

Felk

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answered Oct 18 '11 at 03:19

irreputable

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you should down-vote then. but people eventually will find it out on their own. you need hundreds of lines of extra code to reach what you wanted in the beginning: to know what files are changed. and still there's no way to achieve this with absolute correctness. there is something seriously seriously wrong with the nio team. – irreputable Oct 18 '11 at 03:35
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You misunderstand. Your answer is good and deserves an upvote, and I have no great opinion about the merits of java.nio.file, but the last two words of your answer don't do it justice. Facts weigh more than abuse. – user207421 Oct 18 '11 at 04:44
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How do you deal with multiple watched directories? I’m watching a directory and all its subdirectories, and can’t know in which subdirectory is the modified/created file. – bfontaine Jun 20 '14 at 09:28
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Apache Commons IO has a much simpler directory watcher. Like irreputable, I'm scratching my head over Java's implementation. – Todd Mar 06 '17 at 03:52

score 3 · Answer 2 · edited Jun 03 '16 at 15:33

Granted that you'll want to watch multiple directories (e.g. monitoring a file tree for change) storing the registered WatchKey and it's associated Path in a Map<WatchKey, Path> would also be a viable solution.

When an event is triggered the Map could be asked for the associated Path with the given WatchKey and then the Path of the changed file could be resolved with the help of the Path the WatchKey is associated with.

Dimas · Answer 3 · 2013-06-10T13:39:15.607

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String fullPath = path.toString() + "\\"+ event.context().toString();

:D

edited Jun 10 '13 at 13:39

answered Jun 10 '13 at 10:50

Dimas

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score -5 · Answer 4 · answered Oct 18 '11 at 02:26

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Dependig on what object you got have, you can get absolute path of it:

Path.toAbsolutePath()

File.getAbsoluteFile()

answered Oct 18 '11 at 02:26

Kerai

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java.nio.file.WatchEvent gives me only relative path. How can I get the absolute path of the modified file?

4 Answers4

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