directory copier

DirectoryCopier.java

import java.io.*;

/*
 * Your assignment: This class will copy all the files in one directory to another directories
 * in series (not in parallel). You are to modify this to copy multiple files in parallel using threads.
 */
public class DirectoryCopier {

    private static final int BUFFER_SIZE = 1024;

    /**
     * Copies one directory to another directory
     * Only works with existing directories, and only copies the first level of files
     * TODO: This does not currently recursively copy files. Change it to do so.
     *
     * @param sourceDir The source directory file. Must be an existing directory.
     * @param destinationDir The destination directory file. Must be an existing directory.
     * @throws IOException An IOException raised while copying the files.
     */
    public void copyDirectory(File sourceDir, File destinationDir) throws IOException {
        if (!sourceDir.isDirectory() && !destinationDir.isDirectory()) {
            throw new IllegalArgumentException("Must pass directories into copyDirectory function");
        }

        if (sourceDir.isDirectory() && !destinationDir.exists()) destinationDir.mkdirs();

        FileFilter fileFilter = new FileFilter() {
            public boolean accept(File file) {
                return file.isFile();
            }
        };

        File[] filesToCopy = sourceDir.listFiles(fileFilter);
        for (File sourceFile : filesToCopy) {
            File destinationFile = new File(destinationDir, sourceFile.getName());
            copyFile(sourceFile, destinationFile);
        }


        FileFilter directoryFilter = new FileFilter() {
            public boolean accept(File directory) {
                return directory.isDirectory();
            }
        };

        File[] directories = sourceDir.listFiles(directoryFilter);
//        if (directories.length == 0)
        for (File directory : directories) {
             File destinationDirectory = new File (destinationDir, directory.getName());
             copyDirectory(directory, destinationDirectory);
        }

    }

    /**
     * Copies a file from one place to another.
     * @param source Source file. Must be an actual file.
     * @param destination Destination file.
     * @throws IOException An exception raised while copying the file.
     */
    private void copyFile(File source, File destination) throws IOException {
        if (!source.isFile())
            throw new IllegalArgumentException("Input file must be an actual file!");

        if (!destination.exists())
            destination.createNewFile();
        InputStream in = null;
        OutputStream out = null;

        try {
            in = new FileInputStream(source);
            out = new FileOutputStream(destination);

            byte[] buf = new byte[BUFFER_SIZE];
            int len;
            while ((len = in.read(buf)) > 0) {
                out.write(buf, 0, len);
            }
        }
        finally {
            if (in != null)
                in.close();
            if (out != null)
                out.close();
        }
    }
}