取消 javax.swing 框架中的长任务

Question

我有一个带有 java.swing 组件、ActionListeners 和一个 SwingWorker 的 GUI，用于在单独的线程中执行进一步的代码。我了解 SwingWorker 只能创建一次，不能终止，但可以取消。此外，我认为使用 isCancelled() 方法检查 SwingWorker 状态是一种很好的做法，以防退出 doInBackground() 方法并相应地在 done() 方法中做出反应。例如，如果您在 doInBackground() 方法中有一个循环，并且可以在每次迭代时测试 isCancelled()，则此方法可以正常工作。

但是如何才能真正中断/终止在 doInBackground() 方法中执行的长任务，例如读取大型 csv (>1GB) 或从另一个类调用进程密集型方法？为了说明我的问题，我构建了一个简单的程序，当您选择一个大的输入 csv 时，它会显示我的问题。停止按钮可以在计数器循环中正常工作，但不会终止 csv 导入。

我如何才能真正中断/终止长期持续的流程？如果 SwingWorker 无法做到这一点，我将如何使用线程来做到这一点？ thread.interrupt() 有可能吗？我将如何在我的示例中实现它？

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.net.URISyntaxException;
import java.util.concurrent.TimeUnit;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;
import com.opencsv.CSVReader;

public class MinimalSwing extends JFrame {
// fields
private JButton fileButton, startButton, stopButton;
private JLabel displayLabel;
private File csvIn;
private SwingWorkerClass swingWorker;

// constructor
public MinimalSwing() {
    // set GUI-window properties
    setSize(300, 200);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLocation(200, 200);
    setTitle("MinimalSwing");
    setLayout(new BorderLayout(9, 9));
    setResizable(false);

    // set components
    fileButton = new JButton("Choose File");
    fileButton.addActionListener(new ButtonActionListener());
    getContentPane().add("North", fileButton);
    startButton = new JButton("Start");
    startButton.setEnabled(false);
    startButton.addActionListener(new ButtonActionListener());
    getContentPane().add("West", startButton);
    stopButton = new JButton("Stop");
    stopButton.setEnabled(false);
    stopButton.addActionListener(new ButtonActionListener());
    getContentPane().add("East", stopButton);
    displayLabel = new JLabel("Status...");
    getContentPane().add("South", displayLabel);
}

// csvFileChooser for import
private File getCsv() {
    JFileChooser fc = new JFileChooser();
    int openDialogReturnVal = fc.showOpenDialog(null);
    if(openDialogReturnVal != JFileChooser.APPROVE_OPTION){
        System.out.println("ERROR: Invalid file choice.");
    }
    return fc.getSelectedFile();
}

// csvImporter
private class CsvImporter {
    public void readCsv(File file) throws IOException {
        CSVReader reader = new CSVReader(new FileReader(file));
        String [] nextLine;
        reader.readNext();  
        while ((nextLine = reader.readNext()) != null) {    
            displayLabel.setText("..still reading");
        }
        reader.close();
        displayLabel.setText("..actually done.");
    }
}

// ActionListener
private class ButtonActionListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == fileButton) {
            csvIn = getCsv();
            if(csvIn != null) {
                startButton.setEnabled(true);
                stopButton.setEnabled(true);
            }
        }
        else if(e.getSource() == startButton) {
            fileButton.setEnabled(false);
            startButton.setEnabled(false);
            stopButton.setEnabled(true);
            swingWorker = new SwingWorkerClass();
            swingWorker.execute();
        }
        else {
            fileButton.setEnabled(true);
            startButton.setEnabled(true);
            stopButton.setEnabled(false);
            swingWorker.cancel(true);
        }
    }
}

// swingWorker to interact with further program
private class SwingWorkerClass extends SwingWorker<Boolean, Void> {
    @Override
    protected Boolean doInBackground() throws Exception {
        long t0 = System.currentTimeMillis();
        displayLabel.setText("starting execution...");
        displayLabel.setText("..importing csv");
        CsvImporter csvImporter = new CsvImporter();
        csvImporter.readCsv(csvIn);
        if(isCancelled()) return false; // this cancels after the import, but I want to cancel during the import...
        long t1 = System.currentTimeMillis();
        displayLabel.setText("csv imported in " + String.format("%,d", t1 - t0) + " ms");
        for(short i=1; i<=10; i++) {
            if(isCancelled()) return false; // this works fine as it is called every second
            TimeUnit.SECONDS.sleep(1);
            displayLabel.setText("counter: " + i);
        }
        return true;
    }

    @Override
    public void done() {
        fileButton.setEnabled(true);
        startButton.setEnabled(true);
        stopButton.setEnabled(false);
        if(isCancelled()) {
            displayLabel.setText("Execution cancelled.");
        }
        else {
            displayLabel.setText("Execution succeeded.");
        }
    }
}

// main
public static void main(String[] args) throws URISyntaxException, IOException {
    // launch gui
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            try {
                MinimalSwing frame = new MinimalSwing();
                frame.setVisible(true);
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

}

Answer 1

您可以让您的 CSVImporter 扩展 SwingWorker，而不是再添加一个类 SwingWorkerClass。通过这种方式，您可以获得更多控制权并取消导入任务。

如下所示。

  private class CsvImporter extends SwingWorker<Boolean, Void> {

        public boolean readCsv(File file) throws IOException {
            CSVReader reader = new CSVReader(new FileReader(file));
            String[] nextLine;
            reader.readNext();
            while ((nextLine = reader.readNext()) != null) {
                displayLabel.setText("..still reading");
                if (isCancelled())
                    return false; // this cancels after the import, but I want
                                    // to cancel during the import...
            }
            reader.close();
            displayLabel.setText("..actually done.");
            return true; // read complete
        }

        @Override
        protected Boolean doInBackground() throws Exception {
            long t0 = System.currentTimeMillis();
            displayLabel.setText("starting execution...");
            displayLabel.setText("..importing csv");
            CsvImporter csvImporter = new CsvImporter();
            boolean readStatus = csvImporter.readCsv(csvIn);
            if (readStatus) {
                long t1 = System.currentTimeMillis();
                displayLabel.setText("csv imported in " + String.format("%,d", t1 - t0) + " ms");
                for (short i = 1; i <= 10; i++) {
                    if (isCancelled())
                        return false; // this works fine as it is called every second
                    TimeUnit.SECONDS.sleep(1);
                    displayLabel.setText("counter: " + i);
                }
            }
            return readStatus;
        }
    }