在执行另一个之前等待一个 SwingWorker 完成

Question

我试图在 SO 上找到我的问题的答案，但由于它们的丰富性和多样性，我有些困惑。这是我的问题：我的应用程序比较两个文件并在Swing.JTextPane 中打印出结果。我用一个按钮调用处理文件的代码，为了避免挂起 UI，我用SwingWorker 处理每对文件。这是它的代码：

class ProcessAndPrintTask extends SwingWorker<Void, Void> {
        private Report report;
        Integer reportResult;
        ProcessAndPrintTask(Report report) {
            this.report = report;
            reportResult = null;
        }

        @Override
        protected Void doInBackground() {

            try {
                reportResult = report.getComparator().compareTwoFiles(new FileInputStream(new File(pathToReportsA + report.getFilename())),
                        new FileInputStream(new File(pathToReportsB + report.getFilename())));
            }

            catch (IOException ex) {
                ex.printStackTrace();
            }

            return null;
        }

        @Override
        protected void done() {

            String message = report.getFilename() + ": ";
            if (reportResult != null) {
                switch (reportResult) {
                    case 1:
                        StyleConstants.setBackground(style, Color.GREEN);
                        try {
                            doc.insertString(doc.getLength(), message + "MATCH\n", style);
                        }
                        catch (BadLocationException ex) {ex.printStackTrace();}
                        break;
                    case 0:
                        StyleConstants.setBackground(style, Color.RED);
                        try {
                            doc.insertString(doc.getLength(), message + "NO MATCH\n\n", style);
                            try {
                                for (String s : report.getComparator().getDifferences(
                                        new FileInputStream(new File(pathToReportsA + report.getFilename())),
                                        new FileInputStream(new File(pathToReportsB + report.getFilename())))) {
                                    doc.insertString(doc.getLength(), s + "\n", style);
                                }
                            } catch (Exception ex) {
                                ex.printStackTrace();
                            }
                        }
                        catch (BadLocationException ex) {ex.printStackTrace();}
                        break;
                    case -1:
                        StyleConstants.setBackground(style, Color.CYAN);
                        try {
                            doc.insertString(doc.getLength(), message + "BOTH FILES EMPTY\n", style);
                        }
                        catch (BadLocationException ex) {ex.printStackTrace();}
                        break;
                    default:
                        StyleConstants.setBackground(style, Color.ORANGE);
                        try {
                            doc.insertString(doc.getLength(), message + "PROBLEM\n", style);
                        }
                        catch (BadLocationException ex) {ex.printStackTrace();}

                }
            }
            else {
                StyleConstants.setBackground(style, Color.ORANGE);
                try {
                    doc.insertString(doc.getLength(), message + "FILE OR FILES NOT FOUND\n", style);
                }
                catch (BadLocationException ex) {ex.printStackTrace();}
            }

        }
    }

doInBackground() 进行比较，done() 根据比较结果格式化消息并打印出来。问题是程序不会等到处理并打印一对，因此结果不会按照打开的顺序打印，这可能会让用户感到非常困惑：大多数文件都很小而且真的过去了很快，因此比较似乎在某个时候完成，但仍有更大的文件正在处理。

我读到了使用PropertyChangeListener 的可能性，但我看不出它与使用done() 方法有何不同...我尝试在doInBackground() 中进行比较和打印，但这会弄乱格式（这是意料之中的——在打印完成之前，背景颜色会改变）。我还尝试在调用SwingWorker 的循环内任意时间调用Thread.sleep()，如下所示：

try (FileInputStream reportListExcelFile = new FileInputStream(new File(reportListPath))) {
                Workbook workbook = new XSSFWorkbook(reportListExcelFile);
                Sheet sheet = workbook.getSheetAt(0);
                Iterator<Row> iter = sheet.iterator();

                // skip first row that contains columns names
                iter.next();

                while (iter.hasNext()) {
                    try {Thread.sleep(1000);} catch (Exception ex) {ex.printStackTrace();}
                    Row r = iter.next();
                    String name = r.getCell(0).getStringCellValue();
                    String format = r.getCell(1).getStringCellValue();
                    Report currentReport = new Report(name, format);
                    new ProcessAndPrintTask(currentReport).execute();
                }
            }

它不仅看起来像一个丑陋的拐杖，而且还导致 GUI 挂起，直到所有文件对都被比较。

有解决办法吗？

Answer 1

一旦我完成了OrderedResultsExecutors，它会保持添加任务的顺序以及通知结果的顺序。您所要做的就是为您的案例实施通知方法，例如。写一些Listener 什么的。当然，您可以将 Report 集合传递给 SwingWorker 并在 for 循环中处理它们，但在这种情况下，您将失去多线程，并且所有任务都可能需要更多时间才能以这种单线程方式执行。这就是为什么最好有一个这样的机制的多线程版本，就像这样：

Import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedDeque;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

public class OrderedResultsExecutors extends ThreadPoolExecutor {
    public OrderedResultsExecutors(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
            BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }

    private ConcurrentHashMap<Long, Runnable> startedTasks = new ConcurrentHashMap<>();
    private ConcurrentLinkedDeque<Runnable> finishedTasks = new ConcurrentLinkedDeque<>();
    private AtomicLong toNotify = new AtomicLong(0);
    private AtomicLong submitedCount = new AtomicLong(0);

    @Override
    protected void beforeExecute(Thread t, Runnable r) {
        super.beforeExecute(t, r);
        startedTasks.put(submitedCount.getAndIncrement(), r);
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        super.afterExecute(r, t);
        finishedTasks.add(r);
        finishedTask();
    }

    private void finishedTask() {
        Runnable orderedResult;
        long current;
        while ((orderedResult = startedTasks.get(current = toNotify.get())) != null
                && finishedTasks.contains(orderedResult) && (orderedResult = startedTasks.remove(current)) != null) {
            finishedTasks.remove(orderedResult);
            notify(current, orderedResult);
            toNotify.incrementAndGet();
        }
    }

    private void notify(long order, Runnable result) {
        try {
            System.out.println("order: " + order + " result: " + ((Future)result).get());
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
    }

    public static ExecutorService newFixedThreadPool(int noOfThreads) {
        int corePoolSize = noOfThreads;
        int maximumPoolSize = noOfThreads;
        return new OrderedResultsExecutors(corePoolSize, maximumPoolSize, 0L, TimeUnit.MILLISECONDS,
                new LinkedBlockingQueue<Runnable>());
    }

}

Answer 2

答案（由 Sergiy Medvynskyy 建议）是摆脱循环中调用的“无限多”SwingWorkers，只制作一个使用项目列表来处理和打印的循环，并在 @987654322 内执行循环@。

重构后的代码如下：

class ProcessAndPrintTask extends SwingWorker<Void, Void> {
        private List<Report> reports;
        Integer reportResult;

        ProcessAndPrintTask(List<Report> reports) {
            this.reports = reports;

        }

        @Override
        protected Void doInBackground() {
            for (Report report : reports) {
                try {
                    reportResult = report.getComparator().compareTwoFiles(new FileInputStream(new File(pathToReportsA + report.getFilename())),
                            new FileInputStream(new File(pathToReportsB + report.getFilename())));
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
                String message = report.getFilename() + ": ";
                if (reportResult != null) {
                    switch (reportResult) {
                        case 1:
                            StyleConstants.setBackground(style, Color.GREEN);
                            try {
                                doc.insertString(doc.getLength(), message + "MATCH\n", style);
                            } catch (BadLocationException ex) {
                                ex.printStackTrace();
                            }
                            break;
                        case 0:
                            StyleConstants.setBackground(style, Color.RED);
                            try {
                                doc.insertString(doc.getLength(), message + "NO MATCH\n\n", style);
                                try {
                                    for (String s : report.getComparator().getDifferences(
                                            new FileInputStream(new File(pathToReportsA + report.getFilename())),
                                            new FileInputStream(new File(pathToReportsB + report.getFilename())))) {
                                        doc.insertString(doc.getLength(), s + "\n", style);
                                    }
                                } catch (Exception ex) {
                                    ex.printStackTrace();
                                }
                            } catch (BadLocationException ex) {
                                ex.printStackTrace();
                            }
                            break;
                        case -1:
                            StyleConstants.setBackground(style, Color.CYAN);
                            try {
                                doc.insertString(doc.getLength(), message + "BOTH FILES EMPTY\n", style);
                            } catch (BadLocationException ex) {
                                ex.printStackTrace();
                            }
                            break;
                        default:
                            StyleConstants.setBackground(style, Color.ORANGE);
                            try {
                                doc.insertString(doc.getLength(), message + "PROBLEM\n", style);
                            } catch (BadLocationException ex) {
                                ex.printStackTrace();
                            }

                    }
                } 
                else {
                    StyleConstants.setBackground(style, Color.ORANGE);
                    try {
                        doc.insertString(doc.getLength(), message + "FILE OR FILES NOT FOUND\n", style);
                    } 
                    catch (BadLocationException ex) {
                        ex.printStackTrace();
                    }
                }
            }
            return null;
        }
    }

这里我叫SwingWorker.execute()：

try (FileInputStream reportListExcelFile = new FileInputStream(new File(reportListPath))) {
                Workbook workbook = new XSSFWorkbook(reportListExcelFile);
                Sheet sheet = workbook.getSheetAt(0);
                Iterator<Row> iter = sheet.iterator();
                java.util.List<Report> reports = new ArrayList<>();
                // skip first row that contains columns names
                iter.next();

                while (iter.hasNext()) {
                    Row r = iter.next();
                    String name = r.getCell(0).getStringCellValue();
                    String format = r.getCell(1).getStringCellValue();
                    Report currentReport = new Report(name, format);
                    reports.add(currentReport);
                }
                new ProcessAndPrintTask(reports).execute();
            }

它不是很漂亮，但它可以工作:)