последний пункт задания

FileInputStream inputStream = new FileInputStream(args[1]);
       FileOutputStream outputStream = new FileOutputStream(args[0]);

       Charset utf = Charset.forName("UTF-8");
       Charset windows1251 = Charset.forName("Windows-1251");

       byte[] buffer = new byte[1000];
       inputStream.read(buffer);
       String s = new String(buffer, windows1251);
       buffer = s.getBytes(utf);
       outputStream.write(buffer);