ОС Задачи - Java I/O (June exam session)

package com.company;

import java.io.*;

public class ExamIO {
    public static void manage(String in, String out) throws IOException {
        File folderIn = new File(in);
        if(!(folderIn.exists() && folderIn.isDirectory())){
            System.out.println("ne postoi");
            return;
        }
        File folderOut = new File(out);
        if(folderOut.exists()) {
            cleanFolder(folderOut, true);
        }else {
            folderOut.mkdirs();
        }
        File writable = new File("resources/writable.txt");
        if(!writable.exists()) {
            writable.getParentFile().mkdirs();
            writable.createNewFile();
        }
        BufferedWriter bw = new BufferedWriter(new FileWriter(writable));
        FilenameFilter filter = (dir, name) -> name.endsWith(".dat");
        for (File file:
             folderIn.listFiles(filter)) {
            if(file.isHidden()) {
                System.out.println("zbunet sum " + file.getAbsolutePath());
            }else if(file.canWrite()) {
                System.out.println("pomestuvam  " + file.getAbsolutePath());
                file.renameTo(new File(out + "/" + file.getName()));
            } else {
                System.out.println("dopisuvam " + file.getAbsolutePath());
                try (BufferedReader b = new BufferedReader(new FileReader(file))) {
                    String readLine = "";
                    while ((readLine = b.readLine()) != null) {
                        bw.write(readLine);
                    }
                    bw.flush();
                }
            }
        }
    }

    private static void cleanFolder(File folder, boolean isRoot) {
        for (File f
             : folder.listFiles()) {
            if(f.isDirectory())
                cleanFolder(f, false);
            else
                f.delete();
        }
        if(!isRoot) {
            folder.delete();
        }
    }

    public static void main(String[] args) throws IOException {
        manage("test2", "test1");
    }
}