public static void zipFile(Map<String, Employee> employees,String filename){
        try {
            FileOutputStream fos = new FileOutputStream(filename);
            ZipOutputStream zos= new ZipOutputStream(fos);

            zos.putNextEntry(new ZipEntry("file"));
            ObjectOutputStream oos=new ObjectOutputStream(zos);
            oos.writeObject(employees);
            zos.closeEntry();
            zos.close();
        } catch(FileNotFoundException ex) {
            System.err.format("Nie znaleziono pliku !");
        }catch(IOException ex){
            System.err.println("I/O error: " +ex);
        }
    }

    public static void gzipFile(Map<String, Employee> employees,String filename){
       try {
           FileOutputStream fos = new FileOutputStream(filename);
           GZIPOutputStream gz = new GZIPOutputStream(fos);
           ObjectOutputStream oos=new ObjectOutputStream(gz);
           oos.writeObject(employees);
           gz.close();
           fos.close();
       } catch(FileNotFoundException ex) {
           System.err.format("Nie znaleziono pliku !");
       }catch(IOException ex){
           System.err.println("I/O error: " +ex);
       }
    }

//czytanie z pliku

    public static Map<String,Employee>loadFiles(String filename){

        if(filename.endsWith(".zip")){
            try {
                FileInputStream fis = new FileInputStream(filename);
                ZipInputStream zis = new ZipInputStream(fis);
                ZipEntry ze = zis.getNextEntry();
                ObjectInputStream ois = new ObjectInputStream(zis);
                Map<String, Employee> temp =(Map<String, Employee>) ois.readObject();
                fis.close();
                return temp;
            }catch(FileNotFoundException ex){
                System.err.format("Nie znaleziono pliku !");
                return null;
            }catch(IOException ex){
                System.err.println("I/O error: " +ex);
                return null;
            }catch(ClassNotFoundException ex){
                System.err.println("Nie znaleziono klasy " +ex);
                return null;
            }
        }
        else if(filename.endsWith(".gzip")){
            try{
            FileInputStream fis = new FileInputStream(filename);
            GZIPInputStream gz = new GZIPInputStream(fis);
            ObjectInputStream ois=new ObjectInputStream(gz);
            Map<String,Employee>temp= (Map<String, Employee>) ois.readObject();
            fis.close();
            return temp;
            }catch(FileNotFoundException ex){
                System.err.format("Nie znaleziono pliku !");
                return null;
            }catch(IOException ex){
                System.err.println("I/O error: " +ex);
                return null;
            }catch(ClassNotFoundException ex){
                System.err.println("Nie znaleziono klasy " +ex);
                return null;
            }
        }
        return null;
    }