Java：序列化和反序列化ArrayList

Question

I have a class Book() , Author() and a class CollectionOfBooks() (where I stock all the books in an ArrayList). Then I have my interface where I have a menu where I can add/list/remove/search books. Everything works fine. But, I also want to save my books in a file when I exit the program so when the program ends I call this method( BooksIO() is the class for serialize&deserialize):

public void exitProgram() throws IOException{
        System.out.println("Program shuts down, cya!");
        BooksIO.outputFile(); // to save my books to the file
    }

I am not sure if the books are saved because when I start the program the books don't show up:

public static void main(String[] args) throws IOException, ClassNotFoundException {
        UserInterface menu = new UserInterface();
        BooksIO.inputFile(); // get the books from the saved file to the library
        menu.run();
    }

I am not sure what I am doing wrong, can someone help me? The class for Serialize & DeSerialize :

    public class BooksIO {

            public static  void outputFile() throws IOException{
                CollectionOfBooks library = new CollectionOfBooks(); //where the books are saved in an ArrayList
                FileOutputStream fout=null;
                ObjectOutputStream oos=null;
                try{
                    fout = new FileOutputStream ("stefi.ser");
                    oos=new ObjectOutputStream(fout);
                    // I try to save my library to the file
                    oos.writeObject(library.Books); 

                    System.out.println("Serializing successfully completed");

                    for(Book c: library.Books){
                        System.out.println(c.toString());
                    }
                } catch (IOException ex){
                    System.out.println(ex);
                }finally{
                    try{
                        if(fout!=null) fout.close();
                        if(oos!=null) oos.close();
                    } catch (IOException e){

                    }
                }
            }

            public static void inputFile() throws IOException, ClassNotFoundException{

                CollectionOfBooks library = new//where my books are saved in an ArrayList of type Book CollectionOfBooks();//where my books are saved in an ArrayList of type Book
                ObjectInputStream ois = null;
                try{
                    FileInputStream fin = new FileInputStream("stefi.ser");
                    ois = new ObjectInputStream(fin);
                    // try to get my books from the file and save it in the library
                    library.Books  = (ArrayList<Book>)ois.readObject();
                    System.out.println("Deserializing successfully completed");

                    for(Book c: library.Books){
                        System.out.println(c.toString());
                    }

                }catch (ClassNotFoundException e){
                    System.out.println("The class for this type of objects"+
                            "does not exist in this application!");
                    throw e;
                }finally{
                    try{
                        if(ois!=null){
                            ois.close();
                        }
                    }catch (IOException e){

                    }
                }
            }
        }

Answer 1

Right at the top of your outputFile() method, you are initializing a "library" variable to a new (presumably empty) CollectionOfBooks, and then serializing that.

What you want to do instead is pass the application's instance of CollectionOfBooks into the outputFile() method, and serialize that.

Also, while others may disagree, I find Java serialization to be a bit clunky, and it has some odd edge cases that you need to be aware of. I personally wouldn't use it unless I had to for some reason - I'd use a JSON serialization library, like perhaps GSon, instead.

Answer 2

Just guessing because your question does not include a valid MCVE program yet, but it appears that you're reading in the books but not getting them to where they belong, to the main GUI, quite possibly the UserInterface class (we don't no, since you've not shown us). If so...

Give the UserInterface class a public void updateBooks(CollectionOfBooks books) method, and call this with the updated book collection:

public void updateBooks(CollectionOfBooks collectionOfBooks) {
    this.collectionOfBooks = collectionOfBooks;
}

Change inputFile to return a CollectionOfBooks object:

public static CollectionOfBooks inputFile() throws IOException, ClassNotFoundException{
    //...

}

and then return the collection.

Then in main you could do:

public static void main(String[] args) throws IOException, ClassNotFoundException {
    UserInterface menu = new UserInterface();
    menu.updateBooks(BooksIO.inputFile()); 
    menu.run();
}