ArrayList tempArrayz = new ArrayList();
        tempArrayz = (ArrayList) newArray.get(0);
        File f = new File("WorkSpace");
        f.mkdir();
        File f1 = new File(f.getAbsolutePath(), user.getUserName());
        f1.mkdir();
        File fileo = new File(f1.getAbsolutePath(), user.getUserName() +  ".dat");

        try {
        ObjectOutputStream ou = new ObjectOutputStream(new
        FileOutputStream(fileo));
        ou.writeObject(tempArrayz);
        catch{
                   (Exception e) {
            System.out.println(e.toString());
}
}


Below is the code to read from that and print out the array size

    public void readTheFile()
    {
        
        boolean stopReading = false;
        int numberOfRead = 0;
        while (!stopReading) {
            try {
    
                numberOfRead++;
                File f = new File("WorkSpace");
                f.mkdir();
                File f1 = new File(f.getAbsolutePath(), user.getUserName());
                f1.mkdir(); //make the username folder
                File fileo = new File(f1.getAbsolutePath(),
                                      user.getUserName() + counter + ".dat");
System.out.println(oi.readObject());
                ObjectInputStream oi = new ObjectInputStream(new
                        FileInputStream(fileo));
                    array = (ArrayList) oi.readObject();
                   System.out.println(array.size());
                oi.close();
                stopReading = true;
            } catch (Exception e) {
               if (numberOfRead == 2) {
                    stopReading = true;
                }
    
            }
        }