Problem related to appending the objects in the serialization process

Question

when I enter the inputs as objects, they can be easily saved and able to read in the serialization process but when I add them a second time, objects which are added second time saved in the file, but unable to read them .showing an error related to an invalid type code AC.

try (FileOutputStream file = new FileOutputStream(filename,true);
         ObjectOutputStream out = new ObjectOutputStream(file))
    {
        for (Product pro : productList) {
            out.writeObject(pro);
            System.out.println(pro);
        }


        System.out.println("Object has been saved successfully");
        productList.clear();
    } catch (IOException ex) {
        System.out.println("IOException is caught");
        ex.printStackTrace();
    }

}

Read file code:

try (FileInputStream file = new FileInputStream(filename);
             ObjectInputStream in = new ObjectInputStream(file))
    {
            while ( (p1 = (Product) in.readObject()) != null)
            {

                newProductList.add(p1);
                System.out.println(p1);
                System.out.println("done");
                System.out.println(newProductList.size());

            }
        in.close();
        file.close();
        System.out.println("Reached end of file.");


    } catch (IOException ex) {
            System.err.println("Error while reading product data: " + ex.getMessage());
        }
    catch (ClassNotFoundException e) {
            System.err.println("Class not found during deserialization: " + e.getMessage());
        }

          return newProductList;
}

Please help me fix this error.

I need a correct code to fix my problem