Java Help

Hello guys.
I have been working on my college project for over one week and now I am stuck. Hope you can help
Let's get to the point.

Here is how my GUI looks like:
https://imgur.com/a/GCRFkTe

Everything is connected to mySQL database.
Everything is working properly without a Server. I added server recently, almost everything is working, but i can't figure out how can I do one thing, so:

[code=java]





public class GuestsController implements Initializable {

<DELETED ALL MY FXMLS TO BE SHORTER>

    private Parent root;
    private Stage stage;
    private Scene scene;


    /**
     * This function handles back button.
     * @param event In this case ActionEvent reacts on button press [back button]
     * @throws IOException
     * @return Nothing
     *
     */
    public void backToMenu(ActionEvent event) throws IOException {
        root = FXMLLoader.load(getClass().getResource("mainScene2.fxml"));
        //"here we get our stage"
        stage = (Stage)((Node)event.getSource()).getScene().getWindow();
        scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }

    /**
     * Handles guests adding
     * @param event In this case ActionEvent reacts on button press [Add button]
     * @throws IOException
     */
    public void addGuestsButton(ActionEvent event) throws IOException{
        insertData();
        showGuests();
    }

    /**
     * Handles guests updating
     * @param event In this case ActionEvent reacts on button press [Update button]
     * @throws IOException
     */
    public void updateGuestsButton(ActionEvent event) throws IOException{
        updateRecord();
        showGuests();
    }

    /**
     * Handles guests deleting
     * @param event In this case ActionEvent reacts on button press [delete button]
     * @throws IOException
     */
    public void deleteGuestsButton(ActionEvent event) throws IOException{
        deleteRecord();
        showGuests();
    }

    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) {
        checkGuests();
        showGuests();

    }

    /**
     * This function give us connection to database, if anny exception occurs null is returned
     * @return connection to databse
     *
     */
    //Function which connects us with DB (xaamp mySql)
    public Connection getConnection(){
        Connection conn = null;
        try{
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/relaxmsdb", "root", "");
            //System.out.println("Udalo sie polaczyc");
            return conn;
        }catch (Exception ex){
            System.out.println("Error: " + ex.getMessage());
            return null;
        }
    }

    /**
     * This function
     * @return
     */
    public ObservableList<Guests> getGuestsList(){
        ObservableList<Guests> guestsList = FXCollections.observableArrayList();
        Connection conn = getConnection();
        String query = "SELECT * FROM guests";

        Statement st;
        ResultSet rs;

        try{
            st = conn.createStatement();
            rs = st.executeQuery(query);
            Guests guests ;
            while(rs.next()){
                guests = new Guests(rs.getString("Name"), rs.getString("Surname"), rs.getString("Email"), rs.getInt("Telephone"), rs.getInt("ID_Number"),
                        rs.getString("Hotel"), rs.getInt("RoomNumber"), rs.getDate("StartDate"), rs.getDate("FinishDate"),
                        rs.getInt("standard"), rs.getInt("price"));
                guestsList.add(guests);
            }
        }catch (Exception e){
            e.printStackTrace();
        }
        return guestsList;
    }

    /**
     *
     */
    public void showGuests(){
        ObservableList<Guests> list = getGuestsList();

        columName.setCellValueFactory(new PropertyValueFactory<Guests, String>("name"));
        columnSurname.setCellValueFactory(new PropertyValueFactory<Guests, String>("surname"));
        columnEmail.setCellValueFactory(new PropertyValueFactory<Guests, String>("email"));
        columnTelephone.setCellValueFactory(new PropertyValueFactory<Guests, Integer>("number"));
        columnID_number.setCellValueFactory(new PropertyValueFactory<Guests, Integer>("id_number"));
        columnHotel.setCellValueFactory(new PropertyValueFactory<Guests, String>("hotel"));
        columnRoomNumber.setCellValueFactory(new PropertyValueFactory<Guests, Integer>("room_number"));
        columnStartDate.setCellValueFactory(new PropertyValueFactory<Guests, Date>("StartDate"));
        columnFinishDate.setCellValueFactory(new PropertyValueFactory<Guests, Date>("FinishDate"));
        columnStandard.setCellValueFactory(new PropertyValueFactory<Guests, Integer>("Standard"));
        columnPrice.setCellValueFactory(new PropertyValueFactory<Guests, Integer>("Price"));


        tableViewGuests.setItems(list)  ;
    }

    private void insertData(){
        String query = "INSERT INTO GUESTS VALUES ('" + textFieldName.getText() + "','" + textFieldSurname.getText() + "','" + textFieldEmail.getText() + "'," + textFieldTelephone.getText()
                        + "," + textFieldID_number.getText() + ",'" + textFieldHotel.getText() + "'," + textFieldRoomNumber.getText() + ",'" + textFieldStartDate.getText() +  "', '" +  textFieldFinishDate.getText() + "', "
                + textFieldStandard.getText() + "," + textFieldPrice.getText() + ")";


        String query2 = "INSERT INTO ROOMS (roomID, RoomNumber , price_PN, standard,  available, startdate, finishdate, hotelName ) " +
                "VALUES ("+ null + ", "+ textFieldRoomNumber.getText()  + ", "  +  textFieldPrice.getText() +   ", "  + textFieldStandard.getText() +   ","+ 2 + ", '" + textFieldStartDate.getText() + "','" + textFieldFinishDate.getText() + "', '" + textFieldHotel.getText() +
                "')";

        List <String> passList = new ArrayList<>();
        passList.add(query);
        passList.add(query2);

        Message msg =new Message("_insertGuests", passList);
        Client client  =new Client(25565, "127.0.0.1");
        Message reply = client.executeRequest(msg);

        if(reply.header.equals("1")){
            informationAlertAdd();
        }else{
            warningAlert();
        }

        /*
        executeQuery(query);
        executeQuery(query2);
        if(alertDecision == 0){
            informationAlertAdd();
        }
        else {
            alertDecision--;
        }*/
        clearTextFields();

    }

    private void updateRecord(){
        String query = "UPDATE guests SET name = '" + textFieldName.getText() + "',  surname = '" + textFieldSurname.getText() +
                "',  email = '" + textFieldEmail.getText() + "',  telephone = " + textFieldTelephone.getText() + ",  id_number = " + textFieldID_number.getText()
                + ",  hotel = '" + textFieldHotel.getText() + "',  roomnumber = " + textFieldRoomNumber.getText() + ", startdate =  '" + textFieldStartDate.getText()
                + "', finishdate = '" + textFieldFinishDate.getText() + "'" +  " WHERE id_number = " + textFieldID_number.getText() + ";";


        List <String> passList = new ArrayList<>();
        passList.add(query);
        Message msg =new Message("_updateGuests", passList);
        Client client  =new Client(25565, "127.0.0.1");
        Message reply = client.executeRequest(msg);
        passList.clear();

        if(reply.header.equals("1")){
            informationAlertUpdate();
        }else{
            warningAlert();
        }

        /*
        executeQuery(query);
        if(alertDecision == 0) {
            informationAlertUpdate();
        }else{
            alertDecision--;
        }*/
        clearTextFields();
    }

    /*
    private void updateRecord(){
        String query = "UPDATE guests SET name = '" + textFieldName.getText() + "' WHERE ID_Number = " + textFieldID_number.getText();
        executeQuery(query);
    }*/

    private void deleteRecord(){
        String query = "DELETE FROM guests WHERE id_number = " + textFieldID_number.getText() + "";


        List <String> passList = new ArrayList<>();
        passList.add(query);
        Message msg =new Message("_deleteGuests", passList);
        Client client  =new Client(25565, "127.0.0.1");
        Message reply = client.executeRequest(msg);

        if(reply.header.equals("1")){
            informationAlertDelete();
        }else{
            warningAlert();
        }
        /*
        executeQuery(query);
        if(alertDecision == 0){
            informationAlertDelete();
        }else{
            alertDecision --;
        }*/
        clearTextFields();
    }

    private void executeQuery(String query) {
        Connection conn = getConnection();
        Statement st;
        try{
            st = conn.createStatement();
            st.executeUpdate(query);
        }catch (Exception e){
            warningAlert();
            alertDecision++;
            clearTextFields();
            e.printStackTrace();
        }
    }

    private void checkGuests(){
        String query = "DELETE  FROM `guests` WHERE finishDate < curdate();";
        executeQuery(query);
    }

    private void informationAlertAdd(){
        Alert alert = new Alert(Alert.AlertType.INFORMATION);
        alert.setTitle("Information dialog");
        alert.setContentText("Guest was added successfully");
        alert.setHeaderText("Success");
        alert.showAndWait();
    }

    private void informationAlertUpdate(){
        Alert alert = new Alert(Alert.AlertType.INFORMATION);
        alert.setTitle("Information dialog");
        alert.setContentText("Guest was updated successfully");
        alert.setHeaderText("Success");
        alert.showAndWait();
    }

    private void informationAlertDelete(){
        Alert alert = new Alert(Alert.AlertType.INFORMATION);
        alert.setTitle("Information dialog");
        alert.setContentText("Guest was deleted successfully");
        alert.setHeaderText("Success");
        alert.showAndWait();
    }

    private void warningAlert(){
        Alert alert = new Alert(Alert.AlertType.WARNING);
        alert.setTitle("Warning Dialog");
        alert.setContentText("Provide proper data inputs please!");
        alert.setHeaderText("Something went wrong !");
        alert.showAndWait();
    }

    private void clearTextFields(){
        textFieldName.clear();
        textFieldSurname.clear();
        textFieldEmail.clear();
        textFieldTelephone.clear();
        textFieldID_number.clear();
        textFieldHotel.clear();
        textFieldRoomNumber.clear();
        textFieldStartDate.clear();
        textFieldFinishDate.clear();
        textFieldStandard.clear();
        textFieldPrice.clear();
    }


}
[/code]



Here is my message class which I use to send data between client and server:



[code=java]
package com.example.siechoteli;

import java.io.*;
import java.util.*;

public final class Message implements Serializable
{
    private static final long serialVersionUID = 1234567L;
    public String header;
    public List<String> arguments;
    Message(String header, List<String> arguments)
    {
        this.header = header;
        this.arguments = arguments;
    }
}[/code]

[code=java]package com.example.siechoteli;

import java.io.*;
import java.net.SocketAddress;
import java.sql.*;
import java.text.SimpleDateFormat;
import java.util.*;

public class ServerThread implements Runnable {

    public static int alertDec = 0;

    private String inputHeader;

    private List<String> inputArguments;

    private ObjectOutputStream objectOutputStream;

    SocketAddress socketAddress;

    ServerThread(String inputHeader, List inputArguments, ObjectOutputStream objectOutputStream,
                 SocketAddress socketAddress) {
        this.inputHeader = inputHeader;
        this.inputArguments = inputArguments;
        this.objectOutputStream = objectOutputStream;
        this.socketAddress = socketAddress;
    }


    public void run() {

        try {
            objectOutputStream.writeObject(getResponse());
            objectOutputStream.flush();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }


    }

    public Connection getConnection(){
        Connection conn = null;
        try{
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/relaxmsdb", "root", "");
            //System.out.println("Udalo sie polaczyc");
            return conn;
        }catch (Exception ex){
            System.out.println("Error: " + ex.getMessage());
            return null;
        }
    }


    // Handlers
    private Message _login(){

        // wszyskto działa na czas testow zostawiam wersje bez hasla
       /* Connection conn = getConnection();
        String query = "SELECT * FROM employees";
        Statement st;
        ResultSet rs;
        try{
            st = conn.createStatement();
            rs = st.executeQuery(query);
            while(rs.next()){
                if(rs.getString("login").equals(inputArguments.get(0)) && rs.getString("password").equals(inputArguments.get(1)) ){
                    return new Message("1", null);
                }
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
        return new Message("0", null);*/


        if(inputArguments.get(0).equals("Marian") || inputArguments.get(1).equals("kutas"))
            return new Message("1", null);
        else if(inputArguments.get(0).equals("") || inputArguments.get(1).equals(""))
            return new Message("1", null);
        else
            return  new Message("0", null);

    }


    private Message executeQuery(String query) {
        Connection conn = getConnection();
        Statement st;
        try{
            st = conn.createStatement();
            st.executeUpdate(query);
        }catch (Exception e){
            e.printStackTrace();
            alertDec++;
        }
        return new Message("40", null);
    }

    private Message _insertGuests(){

            executeQuery(inputArguments.get(0));
            executeQuery(inputArguments.get(1));

        if(alertDec == 0){
            return new Message("1", null);
        }else{
            alertDec--;
            return new Message("0", null);
        }
    }

    private  Message _updateGuests(){
        executeQuery(inputArguments.get(0));

        if(alertDec == 0){
            return new Message("1", null);
        }else{
            alertDec--;
            return new Message("0", null);
        }
    }

    private Message _deleteGuests(){
        executeQuery(inputArguments.get(0));

        if(alertDec == 0){
            return new Message("1", null);
        }else{
            alertDec--;
            return new Message("0", null);
        }
    }




    private Message getResponse() {
        Message response;
        // obsluga serwera
        switch (inputHeader) {
            case "_login":
                response = _login();
                break;
            case "_insertGuests":
                response = _insertGuests();
                break;
            case "_updateGuests":
                response = _updateGuests();
                break;
            case "_deleteGuests":
                response = _deleteGuests();
                break;
            default:
                response = new Message("NOP", null);
        }
        return response;
    }

    private void cleanOlderRecords(){
        Connection conn = getConnection();

        String query = "";

    }

}
[/code]


And here is my server thread class. Everything from GuestsController has been already implemented. But how can I implement my getGuestList method with the server? I was thinking about adding a third parameter to the Message class
Guests (a class which I implemented to help me add data to the database).



[code=java]public class Guests {
    private String name;
    private String hotel;
    private Integer room_number;
    private String surname;
    private String email;
    private Integer number;
    private Integer id_number;
    private Integer standard;
    private Integer price;
    private Date startDate;
    private Date finishDate;




    public Guests(String name, String surname, String email, Integer number, Integer id_number, String hotel, Integer room_number, Date startDate, Date finishDate
                    , Integer standard, Integer price) {
        this.name = name;
        this.surname = surname;
        this.email = email;
        this.number = number;
        this.id_number = id_number;
        this.hotel = hotel;
        this.room_number = room_number;
        this.startDate = startDate;
        this.finishDate = finishDate;
        this.standard = standard;
        this.price = price;
    } [/code]




If you have any idea how to solve this problem and include the Server into getGuestList() method I would be grateful :)
Enjoy your day guys :")