javaFX tableview和sqlite的內存泄漏

Question

我正在JavaFX中創建發票系統，並使用帶有“發票”對象的cellValueFactory將sqlite文件中的數據加載到表格視圖中。 我決定加載最新的100個條目以獲得更好的性能，然后通過調用sqlite數據庫並檢索上一個或下一個100個條目來在兩個發票對象之間導航。 每次使用按鈕並顯示下一個100或-100時，它都會使用少量的內存，並且會被保留並且無法恢復，使用時間越長將成為一個問題。

我從其他線程聽說過，這可能是由於偵聽器中的強引用引起的，但我不確定。

沒有錯誤，只有很小的內存泄漏，我無法修復。 我並沒有顯示我的所有代碼，以希望不會使我的代碼過於復雜，但是如果需要，請告訴我。

我是一名高中生，一直在教自己的Swing知識，然后在3個月前轉到javaFX，我對使用GUI編程還是比較陌生，因此，如果我的代碼風格有任何提示或任何不良習慣，請我喜歡學習。

主班（發射器）

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();
        }
    }
}

sqliteDB對象中的相關方法：

sqlitedb中的此方法用於調用初始發票，然后稍后在控制器中調用更多方法。

     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對象：

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

因為每次添加新數據時都在創建新的ChangeListener所以存在內存泄漏。 這是有問題的塊：

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);
}

讓我們來看看為什么要進行逐步分析。

1. 您創建了一個名為custList的新ObservableList ，然后用FilteredList對其進行包裝。
2. 您將ChangeListener添加到兩個控件上的兩個屬性。 在這些偵聽器內部，您調用了FilteredList.setPredicate(Predicate) 。 當您以這種方式引用FilteredList ， ChangeListener必須保留對FilteredList的強引用，而無需保留強引用，如果列表似乎已被垃圾回收，它將在運行時意外拋出NullPointerException 。
3. 您調用了TableView.setItems()以應用新的過濾后的排序項。

到目前為止，一切似乎都可以進行，但是...

您單擊“下一步”並加載了一組新數據，該數據再次調用了此確切方法。

這意味着您將創建另一個 ObservableList ，並包裝另一個 FilteredList 。 然后再次將ChangeListener （x2）添加到相同的屬性。 偵聽器將保留新FilteredList的引用。 然后， 再次設置表格的項目。

再次調用TableView.setItems()時，實際上是在丟棄舊列表。 您以為最終會被垃圾回收，但是...您的聽眾仍然在這兩個屬性中！ 回想一下，所有這些舊偵聽器都保存着舊列表的引用。

您只需一次創建所有這些步驟， 而無需添加任何數據 。 數據輸入后，只需調用TableView.getItems().setAll(newList) 。 這樣，您無需再次重做所有內容並保留其他引用。