Java 7 - NIO - Watcher implementation

One of the new features of Java7 was NIO package. 
Java NIO also known as new input output library as is a set of classes defined under package java.nio.* to access files, file attributes and file systems.

The main classes from this package are:

• Path - to manage file location and directory hierarchy
• Files - to manage file operations

Some functionalities that can be implemented are:

• Walking the file tree
• Watchers - monitoring the creation/modification/deletion of files
• Copy/Create/Delete files from a directory(atomic operations with synchronization)
• Find files using matcher expressions

In the following example we are going to see how to implement a watcher. This is useful when we need a process to monitor when a file is created/modified or deleted in a directory.

Steps in this example:

1- watch for new files in a directory

2- evaluate the mime type of the file

3- if it is a text file it will be copied to other directory.

	import java.io.IOException;
	import java.nio.file.FileSystem;
	import java.nio.file.Files;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.nio.file.StandardCopyOption;
	import java.nio.file.StandardWatchEventKinds;
	import java.nio.file.WatchEvent;
	import java.nio.file.WatchEvent.Kind;
	import java.nio.file.WatchKey;
	import java.nio.file.WatchService;
	public class Watcher{
	public static void main(String[] args) {
	Path folder = Paths.get("C:/Users/user/workspace/TEST1");
	Path destination = Paths.get("C:/Users/user/workspace/TEST2");
	Watcher watcher = new Watcher();
	watcher.watchDirectoryPath(folder, destination);
	}
	public void watchDirectoryPath(Path path, Path destination) {
	FileSystem fs = path.getFileSystem ();
	try(WatchService service = fs.newWatchService()) {
	path.register(service, StandardWatchEventKinds.ENTRY_CREATE,
	StandardWatchEventKinds.ENTRY_MODIFY);
	WatchKey key = null;
	while(true) {
	key = service.take();
	Kind<?> kind = null;
	for(WatchEvent<?> watchEvent : key.pollEvents()) {
	kind = watchEvent.kind();
	if (StandardWatchEventKinds.OVERFLOW == kind) {
	continue;
	} else if ( StandardWatchEventKinds.ENTRY_CREATE == kind) {
	Path newPath = ((WatchEvent<Path>) watchEvent).context();
	if (Files.probeContentType(newPath.getFileName()).equals("text/plain"))
	{
	Files.copy(path.resolve(newPath), destination.resolve(newPath), StandardCopyOption.REPLACE_EXISTING);
	}
	}
	}
	if(!key.reset()) {
	break;
	}
	}
	} catch(IOException ioe) {
	ioe.printStackTrace();
	}
	}
	}

view raw Watcher.java hosted with ❤ by GitHub