How to watch the file system for changes in Java 7 (JDK 7)
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Join For Free• An object implementing the Watchable interface - the Path class is perfect for this job.
• A set of events that we are interested in - we will use StandardWatchEventKind which implements the WatchEvent.Kind<T>.
• An event modifier that qualifies how a Watchable is registered with a WatchService.
• A watcher who watch some watchable – per example, a watcher that watches the File System for changes. The abstract class is java.nio.file.WatchService but we will be using the FileSystem object to create a watcher for the File System.
The below example follows the above scenario:
import java.nio.file.Path; import java.nio.file.Paths; import java.nio.file.StandardWatchEventKind; import java.nio.file.WatchEvent; import java.nio.file.WatchKey; import java.nio.file.WatchService; import java.util.List; public class Main { public static void main(String[] args) { //define a folder root Path myDir = Paths.get("D:/data"); try { WatchService watcher = myDir.getFileSystem().newWatchService(); myDir.register(watcher, StandardWatchEventKind.ENTRY_CREATE, StandardWatchEventKind.ENTRY_DELETE, StandardWatchEventKind.ENTRY_MODIFY); WatchKey watckKey = watcher.take(); List<WatchEvent<?>> events = watckKey.pollEvents(); for (WatchEvent event : events) { if (event.kind() == StandardWatchEventKind.ENTRY_CREATE) { System.out.println("Created: " + event.context().toString()); } if (event.kind() == StandardWatchEventKind.ENTRY_DELETE) { System.out.println("Delete: " + event.context().toString()); } if (event.kind() == StandardWatchEventKind.ENTRY_MODIFY) { System.out.println("Modify: " + event.context().toString()); } } } catch (Exception e) { System.out.println("Error: " + e.toString()); } } }The FileSystem object and the WatchService can also be created like this:
FileSystem fileSystem = FileSystems.getDefault(); WatchService watcher = fileSystem.newWatchService();And the Path (watchable), what we watch, and register it with the WatchService object like this:
Path myDir = fileSystem.getPath("D:/data"); myDir.register(watcher, StandardWatchEventKind.ENTRY_CREATE, StandardWatchEventKind.ENTRY_DELETE, StandardWatchEventKind.ENTRY_MODIFY);
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