本文介绍了SwingWorker和JProgressBar的问题的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我需要将给定的任何图像转换为字节数组以满足加密要求。我正在使用JProgressBar监控转换进度，以防所选图像很大：
I need to convert a any image given to a byte array for encryption requirement. I'm using JProgressBar to monitor the conversion progress in case the chosen image is large:
File p= new File("C:\");
BufferedImage oImg = ImageIO.read(p);
ByteArrayOutputStream ba = new ByteArrayOutputStream();
ImageIO.write(oImg, "jpg", ba);
ba.flush();
ProgressBar pb = new ProgressBar();
Thread thread = new Thread(pb);
thread.join();
pb.fireTask(ba.toByteArray());
我定义了一个 ProgressBar 类，它使用 SwingWorker 如下：
I defined a ProgressBar class that uses SwingWorker as follows:
public class ProgressBar extends JPanel implements Runnable {
private JProgressBar progressBar;
private Task task;
private byte[] imgByteArray;
public void run() {
createGUI();
}
// Create the GUI
private void createGUI() {
JFrame frame = new JFrame("Converting...");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JComponent newContentPane = new ProgressBar();
newContentPane.setOpaque(true);
frame.setContentPane(newContentPane);
JPanel panel = new JPanel();
progressBar = new JProgressBar(0, 100);
progressBar.setBounds(20, 22, 419, 20);
progressBar.setValue(0);
progressBar.setStringPainted(true);
panel.add(progressBar);
add(panel);
setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
frame.pack();
frame.setVisible(true);
}
/**
* Firing the Task
*/
public void fireTask(byte[] imgArray) {
System.arraycopy(imgArray, 0, imgByteArray, 0, imgByteArray.length);
setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
task = new Task();
task.execute();
}
class Task extends SwingWorker<Void, Void> {
@Override
public Void doInBackground() {
for (int i=0; i<=imgByteArray.length; i++){
progressBar.setValue(i);
progressBar.repaint();
try{
Thread.sleep(50);
} catch (InterruptedException err){
}
}
return null;
}
public void done() {
Toolkit.getDefaultToolkit().beep();
setCursor(null); // turn off the wait cursor
}
}
}
遗憾的是，发生了这个错误！
Sadly, this error occurs!
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at ciphers.ProgressBar.fireTask(ProgressBar.java:65)
at ciphers.Images.imageEncryption(Images.java:310)
at ciphers.Images.access$1(Images.java:286)
at ciphers.Images$2.actionPerformed(Images.java:184)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:4
02)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
我不知道我的代码有什么问题！在编写此代码之前，我读了 SwingWorker 和 JProgressBar ，但我觉得我错过了什么！我可以得到一个有用的提示。
I don't know what is wrong with my code! I read SwingWorker and JProgressBar before writing this code but I feel I'm missing something! Can I get a hint that helps.
谢谢：）
推荐答案
SwingWorker 是做什么的。
SwingWorker 提供了一种方法，您可以在事件调度线程的上下文之外执行长时间运行的任务。这意味着您的程序似乎不会被冻结。使用 SwingWorker （使用简单的 Thread ）的好处是它提供了许多易于使用的方法将更新重新同步回EDT，这是为了阻止您违反Swing的单线程规则：不应该在EDT之外的任何线程上创建或修改UI元素。
SwingWorker provides a means by which you can execute long running tasks outside the context of the Event Dispatching Thread. This means that your program won't appear to have become frozen. The benefit of using a SwingWorker (over using a simple Thread) is that it provides a number of easy to use methods to re-sync the updates back to the EDT, which is indented to stop you from breaking the single thread rules of Swing: No UI element should be created or modified on any thread other then the EDT.
仔细查看和和了解更多详情
Tak a closer look at Worker Threads and SwingWorker and javax.swing.SwingWorker<T,V> and Concurrency in Swing for more details
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.ExecutionException;
import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.ImageWriter;
import javax.imageio.event.IIOReadProgressListener;
import javax.imageio.event.IIOWriteProgressListener;
import javax.imageio.stream.ImageInputStream;
import javax.imageio.stream.ImageOutputStream;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class ConvertImage {
public static void main(String[] args) {
new ConvertImage();
}
public ConvertImage() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
TestPane tp = new TestPane();
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(tp);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
tp.convert(new File("C:\\Users\\Shane Whitehead\\Dropbox\\Wallpapers\\animepaper.net_wallpaper_art_anime_aria_duanwu_festival_205050_wonderngo_7680x4800-a8aecc9c.jpg"));
}
});
}
public class TestPane extends JPanel implements ImageConverstionListener {
private JLabel label = new JLabel("Waiting...");
private JProgressBar pb = new JProgressBar();
public TestPane() {
setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridwidth = GridBagConstraints.REMAINDER;
add(label, gbc);
add(pb, gbc);
}
public void convert(File file) {
ConverterWorker worker = new ConverterWorker(file, this);
worker.addPropertyChangeListener(new PropertyChangeListener() {
@Override
public void propertyChange(final PropertyChangeEvent evt) {
if ("progress".equalsIgnoreCase(evt.getPropertyName())) {
pb.setValue((int) evt.getNewValue());
}
}
});
worker.execute();
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
@Override
public void failedToConvertImage(File source, Throwable cause) {
cause.printStackTrace();
JOptionPane.showMessageDialog(this, "<html>Failed to convert " + source + "<br>" + cause.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
}
@Override
public void imageConverted(File source, byte[] bytes) {
JOptionPane.showMessageDialog(this, "Converted image to " + bytes.length + " bytes", "Converted", JOptionPane.INFORMATION_MESSAGE);
}
@Override
public void setMessage(String msg) {
label.setText(msg);
}
}
public interface ImageConverstionListener {
public void failedToConvertImage(File source, Throwable cause);
public void imageConverted(File source, byte[] bytes);
public void setMessage(String msg);
}
public class ConverterWorker extends SwingWorker<ByteArrayOutputStream, String> {
private File source;
private ImageConverstionListener listener;
public ConverterWorker(File source, ImageConverstionListener listener) {
this.source = source;
this.listener = listener;
}
@Override
protected void process(List<String> chunks) {
listener.setMessage(chunks.get(chunks.size() - 1));
}
@Override
protected ByteArrayOutputStream doInBackground() throws Exception {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
publish("Reading image...");
try (ImageInputStream iis = ImageIO.createImageInputStream(source)) {
Iterator<ImageReader> readers = ImageIO.getImageReaders(iis);
if (readers.hasNext()) {
ImageReader reader = readers.next();
reader.addIIOReadProgressListener(new IIOReadProgressListener() {
@Override
public void sequenceStarted(ImageReader source, int minIndex) {
}
@Override
public void sequenceComplete(ImageReader source) {
}
@Override
public void imageStarted(ImageReader source, int imageIndex) {
}
@Override
public void imageProgress(ImageReader source, float percentageDone) {
setProgress(Math.round(percentageDone));
}
@Override
public void imageComplete(ImageReader source) {
}
@Override
public void thumbnailStarted(ImageReader source, int imageIndex, int thumbnailIndex) {
}
@Override
public void thumbnailProgress(ImageReader source, float percentageDone) {
}
@Override
public void thumbnailComplete(ImageReader source) {
}
@Override
public void readAborted(ImageReader source) {
}
});
reader.setInput(iis);
try {
BufferedImage img = reader.read(0);
publish("Converting image...");
try (ImageOutputStream ios = ImageIO.createImageOutputStream(baos)) {
Iterator<ImageWriter> writers = ImageIO.getImageWritersByFormatName("png");
if (writers.hasNext()) {
ImageWriter writer = writers.next();
writer.addIIOWriteProgressListener(new IIOWriteProgressListener() {
@Override
public void imageStarted(ImageWriter source, int imageIndex) {
}
@Override
public void imageProgress(ImageWriter source, float percentageDone) {
setProgress(Math.round(percentageDone));
}
@Override
public void imageComplete(ImageWriter source) {
}
@Override
public void thumbnailStarted(ImageWriter source, int imageIndex, int thumbnailIndex) {
}
@Override
public void thumbnailProgress(ImageWriter source, float percentageDone) {
}
@Override
public void thumbnailComplete(ImageWriter source) {
}
@Override
public void writeAborted(ImageWriter source) {
}
});
writer.setOutput(ios);
try {
writer.write(img);
} finally {
writer.removeAllIIOWriteProgressListeners();
}
}
}
} finally {
reader.removeAllIIOReadProgressListeners();
}
}
}
return baos;
}
@Override
protected void done() {
try {
ByteArrayOutputStream baos = get();
listener.imageConverted(source, baos.toByteArray());
} catch (InterruptedException | ExecutionException ex) {
listener.failedToConvertImage(source, ex);
}
}
}
}
这篇关于SwingWorker和JProgressBar的问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！