The watcher

The watcher can watch one or more directories. The directory has to be registered with the watcher, then when an event occirs a key is released. This key gives details of the event .

• Create a path object that refers to the directory that you want to watch

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Path dir = Paths.get("E:/Development/CodeSource/java7/test");
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• Create a new watch service

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WatchService watcher = FileSystems.getDefault().newWatchService();
WatchService watcher = dir.getFileSystem().newWatchService();
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• Register directory with the watcher(mutiple directories can be registered)

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WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
dir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE, StandardWatchEventKinds.ENTRY_MODIFY);
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• Get the watch key (the application waits here until an event occurs)

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WatchKey watckKey = watcher.take();
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• When an event occurs we poll it and then treat it

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for (WatchEvent<?> event: key.pollEvents()) {}
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• To get the type of event

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if (event.kind() == StandardWatchEventKinds.ENTRY_CREATE) {}
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The tree walker

The tree walker needs to be passed an object of a class that implements the simpleFileVisitor.

Create a Path object refereing to the statring directory.

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Path startingDir = Paths.get("E:/personal/");
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Create a set of visit options

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EnumSet opts = EnumSet.of(FileVisitOption.FOLLOW_LINKS);
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Call the static method of the Files class

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Files.walkFileTree(startingDir, opts, Integer.MAX_VALUE, new FileVisitorImpl());
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Implement the SimpleFileVisitor.

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public class FileVisitorImpl extends SimpleFileVisitor{

public FileVisitResult visitFile(Path file, BasicFileAttributes attr){
System.out.format("FileName: %s", file);
return CONTINUE;
}

public FileVisitResult postVisitDirectory(Path dir, IOException exc) {
System.out.format("Directory: %s%n", dir);
return CONTINUE;
}

public FileVisitResult visitFileFailed(Path file, IOException exc){
System.err.println(exc);
return CONTINUE;
}

}
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