問題描述

我想做什么?

點擊Start JButton，SwingWorker就會執行.在 doInBackground() 方法內部，我將 arrNames 的每個索引傳遞給 publish() 方法，以便在內部顯示JTextArea.

At the click of the Start JButton, the SwingWorker will execute. Inside the doInBackground() method, I am passing each index of arrNames, to the publish() method, so that it can be displayed inside the JTextArea.

發生了什么?

如果我不保留行 System.out.format("Counter : %d%n", counter); 作為評論，在我的 SwingWorker 的 doInBackground() 方法中，SwingWorker 正在按預期工作.雖然如果我將其注釋掉，那么 SwingWorker 停止響應.

If I do not keep line System.out.format("Counter : %d%n", counter); as a comment, in my doInBackground() method of the SwingWorker, then the SwingWorker is working as expected. Though if I comment it out, then the SwingWorker stops responding.

我做錯了嗎?

java version "1.7.0_25"
Java(TM) SE Runtime Environment (build 1.7.0_25-b16)
Java HotSpot(TM) Client VM (build 23.25-b01, mixed mode, sharing)

這是我正在使用的代碼:

Here is the code I am using :

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class SwingWorkerExample1
{
    private JLabel statusLabel;
    private JTextArea tArea;
    private JButton startButton;
    private JButton stopButton;

    private BackgroundTask backgroundTask;

    private ActionListener buttonActions =
                            new ActionListener()
    {
        @Override
        public void actionPerformed(ActionEvent ae)
        {
            JButton source = (JButton) ae.getSource();
            if (source == startButton)
            {
                startButton.setEnabled(false);
                stopButton.setEnabled(true);
                backgroundTask = new BackgroundTask();
                backgroundTask.execute();
            }
            else if (source == stopButton)
            {
                backgroundTask.cancel(true);
                stopButton.setEnabled(false);
                startButton.setEnabled(true);
            }
        }
    };

    private void displayGUI()
    {
        JFrame frame = new JFrame("Swing Worker Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        JPanel contentPane = new JPanel();
        contentPane.setBorder(
            BorderFactory.createEmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(5, 5));

        statusLabel = new JLabel("Status Bar", JLabel.CENTER);

        tArea = new JTextArea(20, 20);
        tArea.setWrapStyleWord(true);
        tArea.setLineWrap(true);        
        JScrollPane textScroller = new JScrollPane();
        textScroller.setBorder(
            BorderFactory.createTitledBorder("Textual OUTPUT : "));
        textScroller.setViewportView(tArea);

        startButton = new JButton("Start");
        startButton.addActionListener(buttonActions);
        stopButton = new JButton("Stop");
        stopButton.setEnabled(false);
        stopButton.addActionListener(buttonActions);
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(startButton);
        buttonPanel.add(stopButton);

        contentPane.add(statusLabel, BorderLayout.PAGE_START);
        contentPane.add(textScroller, BorderLayout.CENTER);
        contentPane.add(buttonPanel, BorderLayout.PAGE_END);

        frame.setContentPane(contentPane);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private class BackgroundTask extends SwingWorker<Void, String>
    {
        private int counter = 0;

        private String[] arrNames = { "US Rates Strategy Cash",
            "Pavan Wadhwa(1-212) 844-4597", "Srini Ramaswamy(1-212) 844-4983",
            "Meera Chandan(1-212) 855-4555", "Kimberly Harano(1-212) 823-4996",
            "Feng Deng(1-212) 855-2555", "US Rates Strategy Derivatives",
            "Srini Ramaswamy(1-212) 811-4999",
            "Alberto Iglesias(1-212) 898-5442",
            "Praveen Korapaty(1-212) 812-3444", "Feng Deng(1-212) 812-2456",
            "US Rates Strategy Derivatives", "Srini Ramaswamy(1-212) 822-4999",
            "Alberto Iglesias(1-212) 822-5098",
            "Praveen Korapaty(1-212) 812-3655", "Feng Deng(1-212) 899-2222" };

        public BackgroundTask()
        {
            statusLabel.setText((this.getState()).toString());
            System.out.println(this.getState());
        }

        @Override
        protected Void doInBackground()
        {
            statusLabel.setText((this.getState()).toString());
            System.out.println(this.getState());
            while (!isCancelled())
            {
                counter %= arrNames.length;
                //System.out.format("Counter : %d%n", counter);
                publish(arrNames[counter]);
                counter++;
            }
            statusLabel.setText((this.getState()).toString());
            System.out.println(this.getState());
            return null;
        }

        @Override
        protected void process(java.util.List<String> messages)
        {
            for (String message : messages)
                tArea.append(String.format(message + "%n"));
        }
    }

    public static void main(String[] args)
    {
        Runnable runnable = new Runnable()
        {
            @Override
            public void run()
            {
                new SwingWorkerExample1().displayGUI();
            }
        };
        EventQueue.invokeLater(runnable);
    }
}

編輯 1:

按照建議，如果我添加 Thread.sleep(...)，它確實可以工作，但它會拋出一個 InterruptedException，如下所示.所以這個技巧奏效了.但這是合法的執行方式嗎?

As suggested, if I add Thread.sleep(...), it does work, though, it throws a InterruptedException as shown below. So the trick works. But is this the legitimate way of performing it ?

C:MineJAVAJ2SEclasses>java SwingWorkerExample1
PENDING
STARTED
java.lang.InterruptedException: sleep interrupted
        at java.lang.Thread.sleep(Native Method)
        at SwingWorkerExample1$BackgroundTask.doInBackground(SwingWorkerExample1.java:108)
        at SwingWorkerExample1$BackgroundTask.doInBackground(SwingWorkerExample1.java:76)
        at javax.swing.SwingWorker$1.call(SwingWorker.java:296)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
        at java.util.concurrent.FutureTask.run(FutureTask.java:166)
        at javax.swing.SwingWorker.run(SwingWorker.java:335)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:724)
DONE

<小時>

編輯 2:

只有 doInBackground() 發生了變化，引發了上述異常:

EDIT 2 :

Only doInBackground() is changed, that raised the above exception :

@Override
protected Void doInBackground()
{
    Runnable runnable = new Runnable()
    {
        @Override
        public void run()
        {
            statusLabel.setText((BackgroundTask.this.getState()).toString());
        }
    };
    EventQueue.invokeLater(runnable);

    System.out.println(this.getState());
    while (!isCancelled())
    {
        counter %= arrNames.length;             
        //System.out.format("Counter : %d%n", counter);
        publish(arrNames[counter]);
        try
        {Thread.sleep(30);}
        catch(InterruptedException ie)
        {ie.printStackTrace();}
        counter++;
    }
    runnable = new Runnable()
    {
        @Override
        public void run()
        {
            statusLabel.setText((BackgroundTask.this.getState()).toString());
        }
    };
    EventQueue.invokeLater(runnable);
    System.out.println(this.getState());
    return null;
}

推薦答案

如果我添加 Thread.sleep(...)，它確實有效，但它會拋出一個中斷異常

if I add Thread.sleep(...), it does work, though, it throws a InterruptedException

顯然產生異常的代碼(復制自 OP 的編輯):

The code that apparently produces the exception (copied from OP's edit):

while (!isCancelled()) {
    counter %= arrNames.length;
    // System.out.format("Counter : %d%n", counter);
    publish(arrNames[counter]);
    try {
        Thread.sleep(30); // throws
    } catch (InterruptedException ie) {
        ie.printStackTrace();
    }
    counter++;
}

不過，原因是取消工作人員的代碼(在 actionListener 中):

The reason, though, is the code that cancels the worker (in the actionListener):

backgroundTask.cancel(true);

它明確告訴工作人員通過 .. 中斷線程來取消.從它的 api 文檔:

which explicitly tells the worker to cancel by .. interrupting the thread. From its api doc:

mayInterruptIfRunning - 如果執行此任務的線程應該被中斷，則為 true；否則，允許完成正在進行的任務

mayInterruptIfRunning - true if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete

順便說一句:捕獲異常并且什么都不做(從而有效地忽略中斷)并不是最好的想法.在這種情況下可能不會造成太大的破壞 - 由于檢查了取消的狀態.典型的工作實現要么在需要時進行一些內部清理之后捕獲并返回，要么根本不處理它.

As an aside: catching the exception and doing nothing (thereby effectively ignoring the interrupt) is not the best of ideas. Probably not too damaging in this case - due to checking the cancelled status. Typical worker implementations either catch and return, after doing some internal cleanup if needed, or don't handle it at all.

這篇關于SwingWorker 沒有響應的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！