Memory leak with javaFX tableview and sqlite

Question

I am creating a invoicing system in JavaFX and loading data from an sqlite file into a tableview using cellValueFactory with a "invoice" object. I decided to load the latest 100 entries for better performance and then have two buttons to navigate between the invoice objects by recalling the sqlite database and retrieving the next 100 up or down. Every time the buttons are used and the next 100 or -100 is displayed, it uses a small amount of memory and is held and not recovered, which the longer its used will become an issue.

I have heard from other threads that this may be caused from strong referencing in listeners but I am not sure of that.

There is no Errors, just a small memory leak that I cannot fix. I am not showing all my code to hopefully not over-complicate my code, but if it is needed please let me know.

I am a high school student and have been teaching my self Swing then moved to javaFX 3 months ago, I am relatively new to programming with GUI, so if there is any tips on my code-style or any bad habits, please I would love to learn.

main class (Launcher)

package main;

import dbUtil.sqlitedb;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.stage.Stage;

import java.util.ArrayList;

//this class launches gui of invoices then distributes the data to the classes.
public class main extends Application {
    /*
    The main class is to access data and process it to and from the sqlitedb object and the invoiceController.
     */


    private boolean saved = true;
    private Parent root;
    private static sqlitedb dataBase;
    private static invoiceDataBaseController invoicesController;
    private Scene scene;
    private static ArrayList<invoiceOBJ> invoiceDataBase;
    private static int indexStart = 100;

    public static void main(String[] args) {

        launch(args);
    }


    public main() {
        invoiceDataBase = new ArrayList<>();



    }


    public void loadInvoices() {
        //dataBase.generateInvoices_test();
        invoiceDataBase = dataBase.listInvoices(indexStart);

    }

    public void setIndexStart(int amount) {
        //the indexStart for the sqlitedb class to use for portioning invoices.
        if (indexStart + amount == 0 || indexStart + amount < 0) {

        } else {
            indexStart += amount;
        }
    }
    // To reset table view's contents with new invoice page.
    public void refreshTable() {
        dataBase.connect();
        invoiceDataBase = dataBase.listInvoices(indexStart);
        invoicesController.addTableItems(invoiceDataBase);
        dataBase.disconnect();


    }



    @Override
    public void start(Stage primaryStage) throws Exception {

        initialize(primaryStage);


    }


    public Scene getScene() {
        return scene;
    }

    public void Loading(Alert alert) {
        // Loading alert before showing main gui
        alert.setHeaderText("Loading Files");
       // System.out.println("loading");
        alert.show();
    }

    public void initialize(Stage stage) {
        try {

            dataBase = new sqlitedb();
            //System.out.println("Loading files");
            //saveInvoicesAndCustomers(generateCustomersAndInvoices());


            FXMLLoader loader = new FXMLLoader(getClass().getResource("main.fxml"));

            Alert alert = new Alert(Alert.AlertType.INFORMATION, "Loading data..");


            Loading(alert);


            loadInvoices();


            root = loader.load();

            invoicesController = loader.getController();
            invoicesController.setStageAndListeners(stage, this, invoiceDataBase);


            scene = new Scene(root);
            scene.getStylesheets().add(getClass().getResource("resources/fxml.css").toExternalForm());
            stage.setTitle("JavaInvoice");
            stage.setScene(scene);


            stage.show();
            alert.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

relevant methods in sqliteDB Object:

This method in the sqlitedb is used to call the initial invoices then call more later within the controller.

     public ArrayList<invoiceOBJ> listInvoices(int indexStart) {
        //invoiceAmount  = invoices to index.
        ArrayList<invoiceOBJ> invoices = new ArrayList<>();
        Long time = System.currentTimeMillis(); //made to test indexing time
        //System.out.println(indexStart + "index start");
        try {
            //System.out.println("in list Invoices");

            stmt = c.createStatement();
            stmt.setFetchSize(1000);

            ResultSet rs = stmt.executeQuery(String.format("SELECT id,year,vin,carModel,condition,licenseState,regNum,stage,vehicleID,paintCode,dateOfInvoice," +
                    "bodyStyle,manufacturer, customerID  FROM invoices LIMIT 100  OFFSET (SELECT COUNT(*) FROM invoices)-%d", indexStart));
            int id;
            String customerID;
            String year;
            String vin;
            String carModel;
            String condition;
            String licenseState;
            String regNum;
            String stage;
            String vehicleID;
            String paintCode;
            String dateOfInvoice;
            String bodyStyle;
            String manufacturer;
            c.setAutoCommit(false);
            stmt.setFetchSize(1000);

            while (rs.next()) {


                id = rs.getInt(1);
                year = rs.getString(2);
                vin = rs.getString(3);
                carModel = rs.getString(4);
                condition = rs.getString(5);
                licenseState = rs.getString(6);
                regNum = rs.getString(7);
                stage = rs.getString(8);
                vehicleID = rs.getString(9);
                paintCode = rs.getString(10);
                dateOfInvoice = rs.getString(11);
                bodyStyle = rs.getString(12);
                manufacturer = rs.getString(13);
                customerID = rs.getString(14);


//                System.out.println(String.format("ID: %d , CustomerID: %s Year: %s, Vin: %s, \ncarModel %s, condition: %s, licenseState: %s \n" +
//                                "regNum: %s, stage: %s vehicleID: %s, paintCode: %s, dateOfInvoice: %s, bodyStyle:%s", id, customerID, year, vin, carModel
//                        , condition, licenseState, regNum, stage, vehicleID, paintCode, dateOfInvoice, bodyStyle));


                //add to invoice list.

                invoices.add(new invoiceOBJ(id,
                        carModel, manufacturer,
                        vin, condition, licenseState,
                        regNum, stage, vehicleID, paintCode,
                        bodyStyle, year, dateOfInvoice, findCustomer(customerID)));


                // System.out.println("added A customer");


            }
            stmt.close();
            rs.close();
            c.close();
            //System.out.println("load complete..");
        } catch (Exception e) {
            e.printStackTrace();
        }
        // System.out.println(System.currentTimeMillis() - time);

        return invoices;

    }
public HashMap<String, String> findCustomer(String id) {

    String sql = String.format("SELECT firstName, lastName,id, date FROM customers WHERE id=%s", id);
    HashMap<String, String> customerData = new HashMap<>();
    try {

        Statement stmt = c.createStatement();
        ResultSet data = stmt.executeQuery(sql);


        customerData.put("firstName", data.getString("firstName"));
        customerData.put("lastName", data.getString("lastName"));
        customerData.put("date", data.getString("date"));
        customerData.put("id", data.getString("id"));

        stmt.close();
        data.close();

    } catch (Exception e) {
        e.printStackTrace();
    }

    return customerData;
}

invoiceController Object:

package main;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.collections.transformation.FilteredList;
import javafx.collections.transformation.SortedList;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.*;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import java.net.URL;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;

public class invoiceDataBaseController implements Initializable {
    main main;
    @FXML
    private Button next = new Button();

    private invoiceLoader customerPage;
    @FXML
    private TableView<invoiceOBJ> invoices = new TableView<>();
    @FXML
    private Button back = new Button();
    @FXML
    private TextField searchField = new TextField();
    @FXML
    private Button confirmButton = new Button();
    @FXML
    private StackPane root = new StackPane();
    @FXML
    private ChoiceBox choice = new ChoiceBox();
    private Stage mainStage;


    public invoiceDataBaseController() {
        customerPage = new invoiceLoader();

    }



    public TextField getSearchField() {
        return searchField;
    }



    //Setup the table of people
    public void setTable() {
        choice.getItems().addAll("ID", "FirstName", "LastName", "Date", "Manufacturer");
        //set specific columns to table.
        TableColumn<invoiceOBJ, String> id = new TableColumn<>("ID:");
        TableColumn<invoiceOBJ, String> firstName = new TableColumn<invoiceOBJ, String>("First Name");
        TableColumn<invoiceOBJ, String> lastName = new TableColumn<invoiceOBJ, String>("Last Name");
        TableColumn<invoiceOBJ, String> dateOfInvoice = new TableColumn<invoiceOBJ, String>("Date");
        TableColumn<invoiceOBJ, String> manufac = new TableColumn<invoiceOBJ, String>("Manufacturer");
        TableColumn<invoiceOBJ, String> model = new TableColumn<invoiceOBJ, String>("Model");
        TableColumn<invoiceOBJ, String> vinNum = new TableColumn<invoiceOBJ, String>("Last 6 VIN");

        invoices.setEditable(true);

        //get data from objects.
        id.setCellValueFactory(p -> p.getValue().getGraphicalData("id"));
        firstName.setCellValueFactory(param -> param.getValue().getCustomer().getFirstName());
        lastName.setCellValueFactory(cellData -> cellData.getValue().getCustomer().getLastName());
        dateOfInvoice.setCellValueFactory(param -> param.getValue().getGraphicalData("dateOfInvoice"));
        manufac.setCellValueFactory(param -> param.getValue().getGraphicalData("manufacturer"));
        model.setCellValueFactory(param -> param.getValue().getGraphicalData("carModel"));
        vinNum.setCellValueFactory(param -> param.getValue().getGraphicalData("vin"));

        //set how dates get sorted
        dateOfInvoice.setComparator((t, t1) -> {
            try {

                SimpleDateFormat format = new SimpleDateFormat("MMM/dd/yyyy");

                return Long.compare(format.parse(t).getTime(), format.parse(t1).getTime());
            } catch (ParseException p) {
                p.printStackTrace();
            }
            return -1;

        });
        id.setComparator(Comparator.comparingInt(Integer::parseInt));
        //end
        //Add values to table view columns and rows.


        //end
        invoices.getColumns().addAll(id, firstName, lastName, dateOfInvoice, manufac, model, vinNum);
        //  dateOfInvoice.setSortType(TableColumn.SortType.DESCENDING);
        id.setSortType(TableColumn.SortType.DESCENDING);

        invoices.getSortOrder().add(id);
        choice.setValue("FirstName");

        //end of making columns,



    }

    public void addTableItems(ArrayList<invoiceOBJ> invoiceDataBase) {
       // System.out.println(Arrays.toString(invoiceDataBase.toArray()) + " table");
        //add invoices list to observable list. (GUI format)
        ObservableList<invoiceOBJ> custList = FXCollections.observableArrayList(invoiceDataBase);
        //Put list to filtered List
        FilteredList<invoiceOBJ> flInvoiceOBJS = new FilteredList(custList, p -> true);

        //add search to filter list values.
        getSearchField().textProperty().addListener(((observable, oldValue, newValue) -> {

            switch (choice.getValue().toString()) {
                case "FirstName":
                    flInvoiceOBJS.setPredicate(p -> p.getCustomer().getFirstName().getValue().toLowerCase().contains(newValue.toLowerCase()));
                    break;
                case "LastName":
                    flInvoiceOBJS.setPredicate(p -> p.getCustomer().getLastName().getValue().toLowerCase().contains(newValue.toLowerCase()));
                    break;
                case "Date":

                    flInvoiceOBJS.setPredicate(p -> p.getGraphicalData("dateOfInvoice").getValue().toLowerCase().contains(newValue.toLowerCase()));
                    break;
                case "Manufacturer":
                    flInvoiceOBJS.setPredicate(p -> p.getGraphicalData("manufacturer").getValue().toLowerCase().contains(newValue.toLowerCase()));
                    break;
                case "ID":
                    flInvoiceOBJS.setPredicate(p -> p.getData().get("id").contains(newValue.toLowerCase()));
                    break;


            }

        }));
        //add search to choiceBox changes.
        choice.valueProperty().addListener(((observable, oldValue, newValue) -> {

            switch (choice.getValue().toString()) {
                case "FirstName":
                    flInvoiceOBJS.setPredicate(p -> p.getCustomer().getFirstName().getValue().toLowerCase().contains(getSearchField().getText().toLowerCase()));
                    break;
                case "LastName":
                    flInvoiceOBJS.setPredicate(p -> p.getCustomer().getLastName().getValue().toLowerCase().contains(getSearchField().getText().toLowerCase()));
                    break;
                case "Date":

                    flInvoiceOBJS.setPredicate(p -> p.getGraphicalData("dateOfInvoice").getValue().toLowerCase().contains(getSearchField().getText().toLowerCase()));
                    break;
                case "Manufacturer":
                    flInvoiceOBJS.setPredicate(p -> p.getData().get("manufacturer").contains(getSearchField().getText().toLowerCase()));
                    break;
                case "ID":
                    flInvoiceOBJS.setPredicate(p -> p.getData().get("manufacturer").contains(getSearchField().getText().toLowerCase()));
                    break;


            }

        }));


        //put filtered list through sorted list
        SortedList<invoiceOBJ> sortedCusts = new SortedList<>(flInvoiceOBJS);
        //add comparators (date)
        sortedCusts.comparatorProperty().bind(invoices.comparatorProperty());
        //finally, add the items to the table view to show
        invoices.setItems(sortedCusts);
    }

private class pageButtonListener implements EventHandler<MouseEvent>  {
        private main root;
        private int indexIncrementor;

        // for indexing new invoices in sqlitedb
    public pageButtonListener(main root, int indexIncrementor){
        this.root =root;
        this.indexIncrementor = indexIncrementor;

    }

    @Override
    public void handle(MouseEvent event) {
        root.setIndexStart(indexIncrementor);
        root.refreshTable();


    }
}
    public void setStageAndListeners(Stage prime, main root, ArrayList<invoiceOBJ> invoiceDataBase) {
        pageButtonListener listener = new pageButtonListener(root,100);
        pageButtonListener backButtonListener = new pageButtonListener(root,-100);
        main = root;
        mainStage = prime;
        setTable();
        addTableItems(invoiceDataBase);
        next.setOnMouseClicked(listener);
        back.setOnMouseClicked(backButtonListener);



    }

    public void getSelected() {
        invoiceOBJ invoice = invoices.getSelectionModel().getSelectedItem();
    }


    @Override
    public void initialize(URL location, ResourceBundle resources) {
        confirmButton.setOnAction(e -> {
            try {

                invoiceOBJ selectedInvoiceOBJ = invoices.getSelectionModel().getSelectedItem();
                if (selectedInvoiceOBJ == null) {
                    Alert noCustomer = new Alert(Alert.AlertType.ERROR, "No Customer Selected!!");
                    noCustomer.setHeaderText("Error, missing invoiceOBJ");
                    noCustomer.show();
                } else {
                    //send user to view invoice INCOMPLETE
                    customerPage.initialize(mainStage, main, selectedInvoiceOBJ);
                }
            } catch (Exception err) {

                err.printStackTrace();
            }
        });

    }
}

InvoiceOBJ:

 package main;

import javafx.beans.property.SimpleStringProperty;
import java.util.HashMap;

public class invoiceOBJ {
    private HashMap<String, String> invoiceData;
    private int customerID;
    private String customerIDToString;
    private customer cust = new customer();

    public SimpleStringProperty getGraphicalData(String key){
        //return hashmap key value into graphical data.
        return new SimpleStringProperty(invoiceData.get(key));
    }


    public HashMap<String, String> getData() {
        return invoiceData;
    }
    public int getCustomerID(){
        return customerID;
    }
    public String getCustomerIDToString(){
        return customerIDToString;
    }
    public customer getCustomer(){
        return cust;
    }

    @Deprecated // reminder to change this god awful system of passing several variables.
    public invoiceOBJ(int idOfInvoice,
                      String carModel, String manufacturer,
                      String vin, String condition, String licenseState,
                      String regNum, String stage, String vehicleID, String paintCode,
                      String bodyStyle, String year, String dateOfInvoice, HashMap<String,String> customerData) {


        cust.setData(customerData);
        invoiceData = new HashMap<>();
        this.customerID = Integer.parseInt(customerData.get("id"));
        this.customerIDToString = customerData.get("id");
        invoiceData.put("id", Integer.toString(idOfInvoice));
        invoiceData.put("carModel", carModel);
        invoiceData.put("manufacturer", manufacturer);
        invoiceData.put("vin", vin);
        invoiceData.put("condition", condition);
        invoiceData.put("licenseState", licenseState);
        invoiceData.put("regNum", regNum);
        invoiceData.put("stage", stage);
        invoiceData.put("vehicleID", vehicleID);
        invoiceData.put("paintCode", paintCode);
        invoiceData.put("bodyStyle", bodyStyle);
        invoiceData.put("year", year);
        invoiceData.put("dateOfInvoice", dateOfInvoice);

        //put into hashmap for easy access of data later.

    }
    public invoiceOBJ(HashMap<String, String> data, HashMap<String,String> customerData) {
        invoiceData = new HashMap<>(data);
        cust.setData(customerData);
        this.customerID = Integer.parseInt(customerData.get("id"));
        this.customerIDToString = Integer.toString(customerID);


    }
}

Answer 1

There is a memory leak because you are creating new ChangeListener whenever you add new data. This is the problematic block:

public void addTableItems(ArrayList<invoiceOBJ> invoiceDataBase) {
    // System.out.println(Arrays.toString(invoiceDataBase.toArray()) + " table");
    //add invoices list to observable list. (GUI format)
    ObservableList<invoiceOBJ> custList = FXCollections.observableArrayList(invoiceDataBase);
    //Put list to filtered List
    FilteredList<invoiceOBJ> flInvoiceOBJS = new FilteredList(custList, p -> true);

    //add search to filter list values.
    getSearchField().textProperty().addListener(((observable, oldValue, newValue) -> {
        switch (choice.getValue().toString()) {
            case "FirstName":
                flInvoiceOBJS.setPredicate(p -> p.getCustomer().getFirstName().getValue().toLowerCase().contains(newValue.toLowerCase()));
                break;
            case "LastName":
                flInvoiceOBJS.setPredicate(p -> p.getCustomer().getLastName().getValue().toLowerCase().contains(newValue.toLowerCase()));
                break;
            case "Date":

                flInvoiceOBJS.setPredicate(p -> p.getGraphicalData("dateOfInvoice").getValue().toLowerCase().contains(newValue.toLowerCase()));
                break;
            case "Manufacturer":
                flInvoiceOBJS.setPredicate(p -> p.getGraphicalData("manufacturer").getValue().toLowerCase().contains(newValue.toLowerCase()));
                break;
            case "ID":
                flInvoiceOBJS.setPredicate(p -> p.getData().get("id").contains(newValue.toLowerCase()));
                break;
        }

    }));
    //add search to choiceBox changes.
    choice.valueProperty().addListener(((observable, oldValue, newValue) -> {

        switch (choice.getValue().toString()) {
            case "FirstName":
                flInvoiceOBJS.setPredicate(p -> p.getCustomer().getFirstName().getValue().toLowerCase().contains(getSearchField().getText().toLowerCase()));
                break;
            case "LastName":
                flInvoiceOBJS.setPredicate(p -> p.getCustomer().getLastName().getValue().toLowerCase().contains(getSearchField().getText().toLowerCase()));
                break;
            case "Date":

                flInvoiceOBJS.setPredicate(p -> p.getGraphicalData("dateOfInvoice").getValue().toLowerCase().contains(getSearchField().getText().toLowerCase()));
                break;
            case "Manufacturer":
                flInvoiceOBJS.setPredicate(p -> p.getData().get("manufacturer").contains(getSearchField().getText().toLowerCase()));
                break;
            case "ID":
                flInvoiceOBJS.setPredicate(p -> p.getData().get("manufacturer").contains(getSearchField().getText().toLowerCase()));
                break;


        }
    }));

    //put filtered list through sorted list
    SortedList<invoiceOBJ> sortedCusts = new SortedList<>(flInvoiceOBJS);
    //add comparators (date)
    sortedCusts.comparatorProperty().bind(invoices.comparatorProperty());
    //finally, add the items to the table view to show
    invoices.setItems(sortedCusts);
}

Let's see why with a step-by-step analysis.

1. You created a new ObservableList called custList , then wrapped it with a FilteredList .
2. You added a ChangeListener to two properties on two controls. Inside these listeners, you called FilteredList.setPredicate(Predicate) . When you reference the FilteredList this way, the ChangeListener has to keep a strong reference of the FilteredList , without keeping strong references it will unexpectedly throw NullPointerException at runtime if the list appears to have been garbage collected.
3. You called TableView.setItems() to apply the new filtered, sorted items.

Everything seems to work so far, but...

You clicked on "next" and loaded a new set of data, which calls this exact method again .

This means that you would create another ObservableList , wrapped with another FilteredList . Then add the ChangeListener (x2) to the same properties again . The listeners are going to hold a reference of the new FilteredList . Then you set the items for the table again .

When you call TableView.setItems() again, you are effectively throwing away the old list. You thought it would be garbage collected eventually, but... Your listeners are still inside the two properties! Recall that all these old listeners are holding references of the old list.

What you need is to create all of those step once, without adding in any data . When the data comes in, simply call TableView.getItems().setAll(newList) . This way you don't redo everything again and hold additional references.