CODEWITHSUNDEEP
javaniowatchservice
Suzan Cioc
Suzan Cioc

Reputation: 30097

How to watch multiple directories with WatchService?

I don't understand, how does 

watcher.take();

will know about which directory to report? Does it report about each directory it was registered against?

dir.register(watcher...

If I have multiple watchers, will they report only about those directories, which were registered against them?

What is the purpose of return value of register()? It looks like it never used in description here: http://docs.oracle.com/javase/tutorial/essential/io/notification.html

Upvotes: 1

Views: 1729

Answers (2)

Heisenbug
Heisenbug

Reputation: 454

We need to register the Folder F1 and all of it subFolders F11 and F12 recursively. And the solution is provided in the official doc itself.

Here's the code segment you need to recursivly folder F1 and all of its subfolder to watchService:

/**
 * Register the given directory and all its sub-directories with the WatchService.
 */
private void registerAll(final Path start) throws IOException {
    // register directory and sub-directories
    Files.walkFileTree(start, new SimpleFileVisitor<Path>() {

        @Override
        public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
                throws IOException {
            dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
            return FileVisitResult.CONTINUE;
        }

    });

}

Incase of more details or incase you dont understand the usage of this code segment. refer to official doc. links provided below.

Official Doc Ref:
https://docs.oracle.com/javase/tutorial/essential/io/notification.html https://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java

Upvotes: 0

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 279890

You use a Path to register a file located by that Path to a WatchService.

If an event occurs, it will be enqueued in the WatchService and you can retrieve it with take(). take() has no idea about the actual Path.

Yes, a WatchService will only report events for those Paths registered with it.

You can use the WatchKey returned by the register method to compare against the WatchKey returned by take(). You can also, obviously, do all the things described in the javadoc.

Upvotes: 3

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