Path

public class PathUsage {
    public void usePath() {
        Path path1 = Paths.get("folder1", "sub1");
        Path path2 = Paths.get("folder2", "sub2");
        path1.resolve(path2); //folder1\sub1\folder2\sub2
        path1.resolveSibling(path2); //folder1\folder2\sub2
        path1.relativize(path2); //..\..\folder2\sub2
        path1.subpath(0, 1); //folder1
        path1.startsWith(path2); //false
        path1.endsWith(path2); //false
        Paths.get("folder1/./../folder2/my.text").normalize(); //folder2\my.text
    }
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        PathUsage usage = new PathUsage();
        usage.usePath();
    }
}

DirectoryStream

public class ListFile {
    public void listFiles() throws IOException {
        Path path = Paths.get("");
        try (DirectoryStream stream = Files.newDirectoryStream(path, "*.*")) {
            for (Path entry: stream) {
                //使用entry
                System.out.println(entry);
            }
        }
    }
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws IOException {
        ListFile listFile = new ListFile();
        listFile.listFiles();
    }
}

Files

public class FilesUtils {
    public void manipulateFiles() throws IOException {
        Path newFile = Files.createFile(Paths.get("new.txt").toAbsolutePath());
        List content = new ArrayList();
        content.add("Hello");
        content.add("World");
        Files.write(newFile, content, Charset.forName("UTF-8"));
        Files.size(newFile);
        byte[] bytes = Files.readAllBytes(newFile);
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        Files.copy(newFile, output);
        Files.delete(newFile);
    }
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws IOException {
        FilesUtils fu = new FilesUtils();
        fu.manipulateFiles();
    }
}

WatchService

public class WatchAndCalculate {
    public void calculate() throws IOException, InterruptedException {
        WatchService service = FileSystems.getDefault().newWatchService();
        Path path = Paths.get("").toAbsolutePath();
        path.register(service, StandardWatchEventKinds.ENTRY_CREATE);
        while (true) {
            WatchKey key = service.take();
            for (WatchEvent<?> event : key.pollEvents()) {
                Path createdPath = (Path) event.context();
                createdPath = path.resolve(createdPath);
                long size = Files.size(createdPath);
                System.out.println(createdPath + " ==> " + size);
            }
            key.reset();
        }
    }
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws Throwable {
        WatchAndCalculate wc = new WatchAndCalculate();
        wc.calculate();
    }
}

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JDK7