JavaFX - SQL查询的后台线程

时间：2013-02-14 15:55:24

标签： javafx-2 javafx

我想知道是否有人可以帮助我解决在JavaFX中创建后台线程的相当恼人的问题！我目前有几个SQL查询将数据添加到当前在JavaFX应用程序线程上运行的UI（参见下面的示例）。但是，当每个查询执行时，它会冻结UI，因为它不在后台线程上运行。我已经查看了使用Task并理解它们的各种示例，但是在进行数据库查询时我无法使它们工作，其中一些需要几秒钟才能运行。

以下是执行查询的方法之一：

public void getTopOrders() {
    customerOrders.clear();
    try {
        Connection con = DriverManager.getConnection(connectionUrl);
        //Get all records from table
        String SQL = "EXEC dbo.Get_Top_5_Customers_week";
        ResultSet rs;
        try (Statement stmt = con.createStatement();) {
            rs = stmt.executeQuery(SQL);

            while (rs.next()) {
                double orderValue = Double.parseDouble(rs.getString(3));
                customerOrders.add(new CustomerOrders(rs.getString(1),
                        rs.getString(2), "£" + formatter.format(orderValue),
                        rs.getString(4).substring(6, 8) + "/" + 
                        rs.getString(4).substring(4, 6) + "/" + 
                        rs.getString(4).substring(0, 4)));
            }
        }

    } catch (SQLException | NumberFormatException e) {
    }
}

将每个已处理的记录添加到ObservableList，该ObservableList链接到TableView或图形，或者只是在标签上设置文本（取决于查询）。如何在后台线程上执行查询，并仍然可以自由使用接口并从查询中更新

提前致谢

2 个答案:

答案 0 :(得分：17)

我创建了一个sample solution，用于使用Task（如Alexander Kirov的评论中所建议的）访问同时执行的线程上的数据库到JavaFX应用程序线程。

样本溶液的相关部分如下：

// fetches a collection of names from a database.
class FetchNamesTask extends DBTask<ObservableList<String>> {
  @Override protected ObservableList<String> call() throws Exception {
    // artificially pause for a while to simulate a long 
    // running database connection.
    Thread.sleep(1000); 

    try (Connection con = getConnection()) {
      return fetchNames(con);
    }
  }

  private ObservableList<String> fetchNames(Connection con) throws SQLException {
    logger.info("Fetching names from database");
    ObservableList<String> names = FXCollections.observableArrayList();

    Statement st = con.createStatement();      
    ResultSet rs = st.executeQuery("select name from employee");
    while (rs.next()) {
      names.add(rs.getString("name"));
    }

    logger.info("Found " + names.size() + " names");

    return names;
  }
}

// loads a collection of names fetched from a database into a listview.
// displays a progress indicator and disables the trigge button for
// the operation while the data is being fetched.
private void fetchNamesFromDatabaseToListView(
        final Button triggerButton, 
        final ProgressIndicator databaseActivityIndicator, 
        final ListView listView) {
  final FetchNamesTask fetchNamesTask = new FetchNamesTask();
  triggerButton.setDisable(true);
  databaseActivityIndicator.setVisible(true);
  databaseActivityIndicator.progressProperty().bind(fetchNamesTask.progressProperty());
  fetchNamesTask.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
    @Override public void handle(WorkerStateEvent t) {
      listView.setItems(fetchNamesTask.getValue());
    }
  });
  fetchNamesTask.runningProperty().addListener(new ChangeListener<Boolean>() {
    @Override public void changed(ObservableValue<? extends Boolean> observable, Boolean wasRunning, Boolean isRunning) {
      if (!isRunning) {
        triggerButton.setDisable(false);
        databaseActivityIndicator.setVisible(false);
      }
    };
  });
  databaseExecutor.submit(fetchNamesTask);
}

private Connection getConnection() throws ClassNotFoundException, SQLException {
  logger.info("Getting a database connection");
  Class.forName("org.h2.Driver");
  return DriverManager.getConnection("jdbc:h2:~/test", "sa", "");
}  

abstract class DBTask<T> extends Task<T> {
  DBTask() {
    setOnFailed(new EventHandler<WorkerStateEvent>() {
      @Override public void handle(WorkerStateEvent t) {
        logger.log(Level.SEVERE, null, getException());
      }
    });
  }
}

// executes database operations concurrent to JavaFX operations.
private ExecutorService databaseExecutor = Executors.newFixedThreadPool(
  1, 
  new DatabaseThreadFactory()
);  

static class DatabaseThreadFactory implements ThreadFactory {
  static final AtomicInteger poolNumber = new AtomicInteger(1);

  @Override public Thread newThread(Runnable runnable) {
    Thread thread = new Thread(runnable, "Database-Connection-" + poolNumber.getAndIncrement() + "-thread");
    thread.setDaemon(true);

    return thread;
  }
}

请注意，一旦您开始同时执行操作，当所有内容都是单线程时，您的编码和UI会比没有任务的默认模式更复杂。例如，在我的示例中，我禁用了启动任务的按钮，因此您无法在后台运行多个任务执行相同的操作（此类处理类似于您可能禁用表单发布按钮以阻止表格被双重发布）。我还在执行长时间运行的数据库任务时向场景添加了一个动画进度指示器，以便用户指示某些事情正在进行。

示例程序输出演示了在长时间运行的数据库操作正在进行时的UI体验（请注意，在获取过程中进度指示器是动画的，这意味着UI响应虽然屏幕截图没有显示这一点）：

databasefetcher

要将实现的额外复杂性和功能与并发任务进行比较，而不是在JavaFX应用程序线程上执行所有内容的实现，您可以看到another version of the same sample which does not use tasks。请注意，在我的情况下使用玩具，本地数据库，基于任务的应用程序的额外复杂性是不必要的，因为本地数据库操作执行得如此之快，但如果您使用长时间运行的复杂查询连接到大型远程数据库，则基于任务方法是值得的，因为它为用户提供了更流畅的UI体验。

答案 1 :(得分：3)

使用jewelsea提供的解决方案进行管理。值得注意的是，如果在不使用列表，表和/或可观察列表的情况下实现此方法，您需要更新UI上的项目（如文本字段或标签），则只需在Platform.runLater中添加更新代码即可。以下是一些显示我的工作解决方案的代码片段。

代码：

public void getSalesData() {
    try {
        Connection con = DriverManager.getConnection(connectionUrl);
        //Get all records from table
        String SQL = "EXEC dbo.Order_Information";
        try (Statement stmt = con.createStatement(); ResultSet rs =
                        stmt.executeQuery(SQL)) {
            while (rs.next()) {

                todayTot = Double.parseDouble(rs.getString(7));
                weekTot = Double.parseDouble(rs.getString(8));
                monthTot = Double.parseDouble(rs.getString(9));
                yearTot = Double.parseDouble(rs.getString(10));
                yearTar = Double.parseDouble(rs.getString(11));
                monthTar = Double.parseDouble(rs.getString(12));
                weekTar = Double.parseDouble(rs.getString(13));
                todayTar = Double.parseDouble(rs.getString(14));
                deltaValue = Double.parseDouble(rs.getString(17));

                yearPer = yearTot / yearTar * 100;
                monthPer = monthTot / monthTar * 100;
                weekPer = weekTot / weekTar * 100;
                todayPer = todayTot / todayTar * 100;

                //Doesn't update UI unless you add the update code to Platform.runLater...
                Platform.runLater(new Runnable() {
                    public void run() {
                        todayTotal.setText("£" + formatter.format(todayTot));
                        weekTotal.setText("£" + formatter.format(weekTot));
                        monthTotal.setText("£" + formatter.format(monthTot));
                        yearTotal.setText("£" + formatter.format(yearTot));
                        yearTarget.setText("£" + formatter.format(yearTar));
                        monthTarget.setText("£" + formatter.format(monthTar));
                        weekTarget.setText("£" + formatter.format(weekTar));
                        todayTarget.setText("£" + formatter.format(todayTar));
                        yearPercent.setText(percentFormatter.format(yearPer) + "%");
                        currentDelta.setText("Current Delta (Week Ends): £"
                                + formatter.format(deltaValue));
                    }
                });

            }
        }

    } catch (SQLException | NumberFormatException e) {
    }
}


    public void databaseThreadTester() {
    fetchDataFromDB();
}

private void fetchDataFromDB() {
    final testController.FetchNamesTask fetchNamesTask = new testController.FetchNamesTask();
    databaseActivityIndicator.setVisible(true);
    databaseActivityIndicator.progressProperty().bind(fetchNamesTask.progressProperty());
    fetchNamesTask.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
        @Override
        public void handle(WorkerStateEvent t) {
        }
    });
    fetchNamesTask.runningProperty().addListener(new ChangeListener<Boolean>() {
        @Override
        public void changed(ObservableValue<? extends Boolean> observable, Boolean wasRunning, Boolean isRunning) {
            if (!isRunning) {
                databaseActivityIndicator.setVisible(false);
            }
        }
    ;
    });
databaseExecutor.submit(fetchNamesTask);
}

abstract class DBTask<T> extends Task {

    DBTask() {
        setOnFailed(new EventHandler<WorkerStateEvent>() {
            @Override
            public void handle(WorkerStateEvent t) {
            }
        });
    }
}

class FetchNamesTask extends testController.DBTask {

    @Override
    protected String call() throws Exception {

        fetchNames();

        return null;
    }

    private void fetchNames() throws SQLException, InterruptedException {
        Thread.sleep(5000);
        getTopOrders();
        getSalesData();
    }
}

唯一似乎不适用于此实现的是以下内容，不确定为什么它不起作用但它不会绘制图形。

public void addCricketGraphData() {

    yearChart.getData().clear();
    series.getData().clear();
    series2.getData().clear();
    try {
        Connection con = DriverManager.getConnection(connectionUrl);
        //Get all records from table
        String SQL = "...omitted...";
        try (Statement stmt = con.createStatement(); ResultSet rs =
                        stmt.executeQuery(SQL)) {
            while (rs.next()) {
                Platform.runLater(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            series.getData().add(new XYChart.Data<String, Number>(rs.getString(1),
                                    Double.parseDouble(rs.getString(7))));
                            series2.getData().add(new XYChart.Data<String, Number>(rs.getString(1),
                                    Double.parseDouble(rs.getString(8))));
                        } catch (SQLException ex) {
                            Logger.getLogger(testController.class.getName()).log(Level.SEVERE, null, ex);
                        }
                    }
                });

            }
        }

    } catch (SQLException | NumberFormatException e) {
    }
    yearChart = createChart();
}

 protected LineChart<String, Number> createChart() {
    final CategoryAxis xAxis = new CategoryAxis();
    final NumberAxis yAxis = new NumberAxis();

    // setup chart
    series.setName("Target");
    series2.setName("Actual");
    xAxis.setLabel("Period");
    yAxis.setLabel("£");

    //Add custom node for each point of data on the line chart.
    for (int i = 0; i < series2.getData().size(); i++) {
        nodeCounter = i;
        final int value = series.getData().get(nodeCounter).getYValue().intValue();
        final int value2 = series2.getData().get(nodeCounter).getYValue().intValue();
        int result = value2 - value;

        Node node = new HoveredThresholdNode(0, result);
        node.toBack();
        series2.getData().get(nodeCounter).setNode(node);
    }

    yearChart.getData().add(series);
    yearChart.getData().add(series2);

    return yearChart;
}
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