ObjectInputStream returns an empty object

Question

So I'm trying to send an Object from a client to the server and then I do something with this object. I verified that when being sent the object contains data. When I'm in the debugger reading my object all of its properties are null.

Below is where I send the object:

private class registerUser extends Task<Void>
{
        Users user;
        private static final String code = ".register";
        private static final String host = "localhost";
        private static final int portNumber = 4444;
        private clientThread clientThread;


    public registerUser(Users user)
    {
        this.user = user;
    }

    @Override
    protected Void call() throws Exception
    {
        try
        {
            Socket socket = new Socket(host, portNumber);
            Thread.sleep(1000);

            //Setup I/O
            ObjectOutputStream outToServerObject = new ObjectOutputStream(socket.getOutputStream());
            //PrintWriter serverOutString = new PrintWriter(socket.getOutputStream(), false);
            InputStream serverInString = socket.getInputStream();

            //serverOutString.println(code);
           // serverOutString.flush();

            outToServerObject.writeObject(user);
            outToServerObject.flush();
        }
        catch (IOException e)
        {
            System.err.println("Fatal Connection error!");
            e.printStackTrace();
        }
        return null;
    }

The above task is then used when I press a button in my GUI as shown below:

public void btn_registerUser(ActionEvent actionEvent) throws IOException
{

        user.setUserName(txt_Username.getText());
        user.setFirstName(txt_FirstName.getText());
        user.setLastName(txt_LastName.getText());
        user.setCity(txt_City.getText());
        user.setBirthday(date_Birthday.getValue());


        Task<Void> task = new registerUser(user);
        Thread thread = new Thread(task);
        thread.setDaemon(true);
        thread.start();

}

The code in the server where object is received:

//Setup I/O
this.clientOut = new PrintWriter(socket.getOutputStream(), false);
ObjectInputStream inFromClientObject = new ObjectInputStream(socket.getInputStream());


// Scanner in = new Scanner(socket.getInputStream());
Users user = (Users) inFromClientObject.readObject();
doSomething(user);

And the User.java class which is the object at debate

public class Users implements Serializable
{

    /*
    Variables
    TODO Create a friend list
    */
    private transient IntegerProperty userID;
    private transient StringProperty userName;
    private transient StringProperty firstName;
    private transient StringProperty lastName;
    private transient StringProperty city;
    private transient ObjectProperty<LocalDate> birthday;
    private transient ListProperty<String> musicGenre;
    private transient List<String> musicGenres = new ArrayList<>();
    /**
     * Default constructor.
     */
    public Users()
    {
        this(null,null,null,null,null);
    }

    /**
     * Constructor with some initial data.
     * Takes in a {@code String} and sets a reference
     *
     * @param userName
     *
     */
    public Users(String userName,  String firstName, String lastName, String city, LocalDate birthday)
    {
        this.userName = new SimpleStringProperty(userName);
        this.userID = new SimpleIntegerProperty();
        this.firstName = new SimpleStringProperty(firstName);
        this.lastName = new SimpleStringProperty(lastName);
        this.city = new SimpleStringProperty(city);
        this.birthday = new SimpleObjectProperty<LocalDate>(birthday);
        ObservableList<String> observableList = FXCollections.observableArrayList(this.musicGenres);
        this.musicGenre = new SimpleListProperty<String>(observableList);

    }
}

I've left out the getters and setters as this questions is getting long already

So in the debugger when running the server all the properties of the user are null when I doSomething(user)

*EDIT The suggestions are working out but I've gotten a problem with

private List<String> musicGenreList = new ArrayList<>();
ObservableList<String> observableList = FXCollections.observableArrayList(musicGenreList);
private ListProperty<String> musicGenre = new SimpleListProperty<String>(observableList);

It's the only way I can add items to the ListProperty but the observableList can't be serialized

Answer 1

Like James_D said basically I have to create custom WriteExternal and ReadExternal

in the Users.java The changes need to be made

public class Users implements Externalizable
{
    public Users(String userName,  String firstName, String lastName, String city, LocalDate birthday)
    {
        setUserName(userName);
        setFirstName(firstName);
        setBirthday(birthday);
    }

    private IntegerProperty userID = new SimpleIntegerProperty(this, "id");
    private StringProperty userName = new SimpleStringProperty(this, "userName');
    private ObjectProperty<LocalDate> birthday = new SimpleObjectProperty<>(this, "birthday");

    //Create setters and getters...

    @Override
    public void writeExternal(ObjectOutput out) throws IOException
    {
        out.writeInt(getUserID());
        out.writeObject(getUserName());
        out.writeObject(getBirthday());
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
    {
        setUserID((int) in.readInteger());
        setUserName((String) in.readObject());
        setBirthday((LocalDate) in.readObject());
    }
}

However I haven't been able to serialize a ListProperty using the below method

private ObservableList<String> observableList = FXCollections.observableArrayList();
private ListProperty<String> newList = new SimpleListProperty<>(this, "musicGenre", observableList);

For my needs the ListProperty needs to be instantiated this way as I need to add String items to it using user.newListProperty().get().add("String") and without the ObservableList I can't do this

If anyone knows a way around this it'd be appreciated