Java 为什么JFrame在一种情况下是空白的，而在另一种情况下不是空白的？（简单的SwingWorker示例）
=============================================== 由于评论太长，请在此添加此内容： 我看得出我不清楚。运行MaintTest/main时，JFrame with Test按钮不是问题所在。单击测试按钮时显示的JFrame就是问题所在 注释掉FileUtils.copyrltofile try块会使第二个JFrame显示得如此短暂，以至于不清楚它是否显示了标签和程序条。（带有测试按钮的初始JFrame会正常显示，当我单击测试按钮时，第二个JFrame会出现一瞬间并消失。带有测试按钮的JFrame会保持不变，正如预期的那样。我不会连续复制“一个测试按钮6次”。这听起来像是设置错误，可能吧？） 是的，copyURLToFile正在阻塞，但在调用copyURLToFile之前，我启动了第二个JFrame的并发显示，所以它不应该在单独的线程中运行吗？我有理由知道它的作用。在派生此代码的原始应用程序中，有时会根据需要显示第二个JFrame JFrame显示有时总是说setVisible必须最后调用，但这并不能解决我的情况。这似乎与并发性和Swing有关，我不理解 =============================================== 通常我可以通过谷歌找到答案（更多的时候是这样）。我一定是遗漏了什么 我已经把它缩减到了我实际代码的一小部分，但仍然没有得到启发。抱歉，如果它仍然有点大，但很难进一步压缩它 有3个java文件。本文引用了commons-io-2.5.jar。我正在Eclipse Neon中编码/运行 如果我运行Java 为什么JFrame在一种情况下是空白的，而在另一种情况下不是空白的？（简单的SwingWorker示例）,java,swing,jframe,Java,Swing,Jframe,=============================================== 由于评论太长，请在此添加此内容： 我看得出我不清楚。运行MaintTest/main时，JFrame with Test按钮不是问题所在。单击测试按钮时显示的JFrame就是问题所在 注释掉FileUtils.copyrltofile try块会使第二个JFrame显示得如此短暂，以至于不清楚它是否显示了标签和程序条。（带有测试按钮的初始JFrame会正常显示，当我单击测试按钮时，第二个JFrame会
ProgressBarmain（）JFramemain测试main（）MainTestProgressBar感谢@MadProgrammer的评论：
我可以告诉您，您可能看不到ProgressBar框架，因为FileUtils.copyURLToFile将被阻止，直到它完成，在这种情况下，您真的应该使用SwingWorker 我在教程中阅读了关于SwingWorker的内容，随后修改了MainFrame.java模块，如下所示：
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.SwingWorker;
import org.apache.commons.io.FileUtils;
public class MainFrame extends JFrame implements ActionListener {
JButton jButton = new JButton();
static ProgressBar status;
static URL url;
public MainFrame() {
// Set up the content pane.
Container contentPane = this.getContentPane();
contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
jButton.setAlignmentX(Component.CENTER_ALIGNMENT);
jButton.setText("Test");
jButton.setActionCommand("Test");
jButton.addActionListener(this);
contentPane.add(jButton);
setup();
}
private void setup() {
Toolkit tk;
Dimension screenDims;
tk = Toolkit.getDefaultToolkit();
screenDims = tk.getScreenSize();
this.setLocation((screenDims.width - this.getWidth()) / 2, (screenDims.height - this.getHeight()) / 2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.pack();
this.setVisible(true);
}
public static void downloadExecutable(String str) {
url = null;
try {
url = new URL("http://pegr-converter.com/download/test.jpg");
} catch (MalformedURLException exc) {
JOptionPane.showMessageDialog(null, "Unexpected exception: " + exc.getMessage());
return;
}
if (url != null) {
String[] options = { "OK", "Change", "Cancel" };
int response = JOptionPane.NO_OPTION;
File selectedFolder = new File(getDownloadDir());
File selectedLocation = new File(selectedFolder, str + ".jpg");
while (response == JOptionPane.NO_OPTION) {
selectedLocation = new File(selectedFolder, str + ".jpg");
String msgStr = str + ".jpg will be downloaded to the following location:\n"
+ selectedLocation.toPath();
response = JOptionPane.showOptionDialog(null, msgStr, "Pegr input needed",
JOptionPane.YES_NO_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, options, options[0]);
if (response == JOptionPane.NO_OPTION) {
// Prompt for file selection.
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
fileChooser.setCurrentDirectory(selectedFolder);
fileChooser.showOpenDialog(null);
selectedFolder = fileChooser.getSelectedFile();
}
}
if (response == JOptionPane.YES_OPTION) {
int size = 0;
URLConnection conn;
try {
conn = url.openConnection();
size = conn.getContentLength();
} catch (IOException exc) {
System.out.println(exc.getMessage());
}
//System.out.println("javax.swing.SwingUtilities.isEventDispatchThread=" + javax.swing.SwingUtilities.isEventDispatchThread());
File destination = new File(selectedFolder, str + ".jpg");
status = new ProgressBar("Downloading " + str + ".jpg", destination, size);
SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>() {
@Override
protected Void doInBackground() throws Exception {
try {
FileUtils.copyURLToFile(url, destination, 10000, 300000);
} catch (IOException exc) {
JOptionPane.showMessageDialog(null, "Download failed.");
}
return null;
}
public void done() {
status.close();
}
};
worker.execute();
}
}
}
public static String getDownloadDir() {
String home = System.getProperty("user.home");
File downloadDir = new File(home + "/Downloads/");
if (downloadDir.exists() && !downloadDir.isDirectory()) {
return home;
} else {
downloadDir = new File(downloadDir + "/");
if ((downloadDir.exists() && downloadDir.isDirectory()) || downloadDir.mkdirs()) {
return downloadDir.getPath();
} else {
return home;
}
}
}
@Override
public void actionPerformed(ActionEvent arg0) {
downloadExecutable("test");
}
}
导入java.awt.Component；
导入java.awt.Container；
导入java.awt.Dimension；
导入java.awt.Toolkit；
导入java.awt.event.ActionEvent；
导入java.awt.event.ActionListener；
导入java.io.File；
导入java.io.IOException；
导入java.net.MalformedURLException；
导入java.net.URL；
导入java.net.URLConnection；
导入javax.swing.BoxLayout；
导入javax.swing.JButton；
导入javax.swing.JFileChooser；
导入javax.swing.JFrame；
导入javax.swing.JOptionPane；
导入javax.swing.SwingWorker；
导入org.apache.commons.io.FileUtils；
公共类大型机扩展JFrame实现ActionListener{
JButton JButton=新JButton（）；
静态进度条状态；
静态URL；
公共主机（）{
//设置内容窗格。
容器contentPane=this.getContentPane（）；
setLayout（新的BoxLayout（contentPane，BoxLayout.Y_轴））；
jButton.setAlignmentX（组件中心对齐）；
setText（“测试”）；
setActionCommand（“测试”）；
addActionListener（这个）；
contentPane.add（jButton）；
设置（）；
}
私有无效设置（）{
工具包tk；
尺寸屏幕尺寸；
tk=Toolkit.getDefaultToolkit（）；
screenDims=tk.getScreenSize（）；
this.setLocation（（screenDims.width-this.getWidth（））/2，（screenDims.height-this.getHeight（））/2）；
此.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）；
这个包（）；
此.setVisible（true）；
}
公共静态void下载可执行文件（字符串str）{
url=null；
试一试{
url=新url（“http://pegr-converter.com/download/test.jpg");
}捕获（异常异常异常exc）{
showMessageDialog（null，“意外异常：”+exc.getMessage（））；
返回；
}
如果（url！=null）{
字符串[]选项={“确定”、“更改”、“取消”}；
int response=JOptionPane.NO_选项；
File selectedFolder=新文件（getDownloadDir（））；
File selectedLocation=新文件（selectedFolder，str+“.jpg”）；
while（response==JOptionPane.NO_选项）{
selectedLocation=新文件（selectedFolder，str+“.jpg”）；
字符串msgStr=str+“.jpg将下载到以下位置：\n”
+selectedLocation.toPath（）；
response=JOptionPane.showOptionDialog（null，msgStr，“需要Pegr输入”，
JOptionPane.YES\u NO\u CANCEL\u选项，JOptionPane.QUESTION\u消息，null，options，options[0]）；
if（response==JOptionPane.NO_选项）{
//提示选择文件。
JFileChooser fileChooser=新的JFileChooser（）；
fileChooser.setFileSelectionMode（仅限JFileChooser.DIRECTORIES_）；
fileChooser.setCurrentDirectory（selectedFolder）；
fileChooser.showOpenDialog（null）；
selectedFolder=fileChooser.getSelectedFile（）；
}
}
if（response==JOptionPane.YES\u选项）{
int size=0；
连接连接；
试一试{
conn=url.openConnection（）；
size=conn.getContentLength（）；
}捕获（IOException）{
System.out.println（exc.getMessage（））；
}
//System.out.println（“javax.swing.SwingUtilities.isEventDispatchThread=“+javax.swing.SwingUtilities.isEventDispatchThread（））；
文件目的地=新文件（selectedFolder，str+“.jpg”）；
状态=新进度条（“D
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import org.apache.commons.io.FileUtils;
public class MainFrame extends JFrame implements ActionListener {
JButton jButton = new JButton();
public MainFrame() {
// Set up the content pane.
Container contentPane = this.getContentPane();
contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
jButton.setAlignmentX(Component.CENTER_ALIGNMENT);
jButton.setText("Test");
jButton.setActionCommand("Test");
jButton.addActionListener(this);
contentPane.add(jButton);
setup();
}
private void setup() {
Toolkit tk;
Dimension screenDims;
tk = Toolkit.getDefaultToolkit();
screenDims = tk.getScreenSize();
this.setLocation((screenDims.width - this.getWidth()) / 2, (screenDims.height - this.getHeight()) / 2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.pack();
this.setVisible(true);
}
public static void downloadExecutable(String str) {
URL url = null;
try {
url = new URL("http://pegr-converter.com/download/test.jpg");
} catch (MalformedURLException exc) {
JOptionPane.showMessageDialog(null, "Unexpected exception: " + exc.getMessage());
return;
}
if (url != null) {
String[] options = { "OK", "Change", "Cancel" };
int response = JOptionPane.NO_OPTION;
File selectedFolder = new File(getDownloadDir());
File selectedLocation = new File(selectedFolder, str + ".jpg");
while (response == JOptionPane.NO_OPTION) {
selectedLocation = new File(selectedFolder, str + ".jpg");
String msgStr = str + ".jpg will be downloaded to the following location:\n"
+ selectedLocation.toPath();
response = JOptionPane.showOptionDialog(null, msgStr, "Pegr input needed",
JOptionPane.YES_NO_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, options, options[0]);
if (response == JOptionPane.NO_OPTION) {
// Prompt for file selection.
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
fileChooser.setCurrentDirectory(selectedFolder);
fileChooser.showOpenDialog(null);
selectedFolder = fileChooser.getSelectedFile();
}
}
if (response == JOptionPane.YES_OPTION) {
int size = 0;
URLConnection conn;
try {
conn = url.openConnection();
size = conn.getContentLength();
} catch (IOException exc) {
System.out.println(exc.getMessage());
}
File destination = new File(selectedFolder, str + ".jpg");
ProgressBar status = new ProgressBar("Downloading " + str + ".jpg", destination, size);
try {
FileUtils.copyURLToFile(url, destination, 10000, 300000);
} catch (IOException exc) {
JOptionPane.showMessageDialog(null, "Download failed.");
return;
}
status.close();
}
}
}
public static String getDownloadDir() {
String home = System.getProperty("user.home");
File downloadDir = new File(home + "/Downloads/");
if (downloadDir.exists() && !downloadDir.isDirectory()) {
return home;
} else {
downloadDir = new File(downloadDir + "/");
if ((downloadDir.exists() && downloadDir.isDirectory()) || downloadDir.mkdirs()) {
return downloadDir.getPath();
} else {
return home;
}
}
}
@Override
public void actionPerformed(ActionEvent arg0) {
downloadExecutable("test");
}
}
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Timer;
import java.util.TimerTask;
import javax.imageio.ImageIO;
import javax.swing.BoxLayout;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JProgressBar;
import javax.swing.SwingConstants;
import org.apache.commons.io.FileUtils;
public class ProgressBar {
private String title;
private File outputFile;
private int size;
private ProgressTimerTask task;
JFrame frame;
JLabel jLabelProgressTitle;
JProgressBar jProgressBarProportion;
public ProgressBar(String title, File output, int size) {
this.title = title;
this.outputFile = output;
this.size = size;
frame = new JFrame("BoxLayoutDemo");
jProgressBarProportion = new JProgressBar();
jProgressBarProportion.setPreferredSize(new Dimension(300, 50));
jLabelProgressTitle = new JLabel();
jLabelProgressTitle.setHorizontalAlignment(SwingConstants.CENTER);
jLabelProgressTitle.setText("Progress");
jLabelProgressTitle.setPreferredSize(new Dimension(300, 50));
//Set up the content pane.
Container contentPane = frame.getContentPane();
contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
jLabelProgressTitle.setAlignmentX(Component.CENTER_ALIGNMENT);
contentPane.add(jLabelProgressTitle);
jProgressBarProportion.setAlignmentX(Component.CENTER_ALIGNMENT);
contentPane.add(jProgressBarProportion);
setup();
task = new ProgressTimerTask(this, outputFile, size);
Timer timer = new Timer();
timer.scheduleAtFixedRate(task, 0, 500);
}
private void setup() {
Toolkit tk;
Dimension screenDims;
frame.setTitle("Test");
tk = Toolkit.getDefaultToolkit();
screenDims = tk.getScreenSize();
frame.setLocation((screenDims.width - frame.getWidth()) / 2, (screenDims.height - frame.getHeight()) / 2);
jLabelProgressTitle.setText(title);
jProgressBarProportion.setVisible(true);
jProgressBarProportion.setMinimum(0);
jProgressBarProportion.setMaximum(size);
jProgressBarProportion.setValue((int) outputFile.length());
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
public void close() {
task.cancel();
frame.dispose();
}
public static void main(String[] args) throws InterruptedException {
ProgressBar progBar = new ProgressBar("Test Title", new File(MainFrame.getDownloadDir() + "test.jpg"), 30000);
Thread.sleep(3000);
progBar.close();
}
}
class ProgressTimerTask extends TimerTask {
ProgressBar frame;
File outputFile;
int size;
public ProgressTimerTask(ProgressBar progressBar, File outputFile, int size) {
this.frame = progressBar;
this.outputFile = outputFile;
this.size = size;
}
public void run() {
frame.jProgressBarProportion.setValue((int) outputFile.length());
System.out.println("Running");
}
}
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.SwingWorker;
import org.apache.commons.io.FileUtils;
public class MainFrame extends JFrame implements ActionListener {
JButton jButton = new JButton();
static ProgressBar status;
static URL url;
public MainFrame() {
// Set up the content pane.
Container contentPane = this.getContentPane();
contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
jButton.setAlignmentX(Component.CENTER_ALIGNMENT);
jButton.setText("Test");
jButton.setActionCommand("Test");
jButton.addActionListener(this);
contentPane.add(jButton);
setup();
}
private void setup() {
Toolkit tk;
Dimension screenDims;
tk = Toolkit.getDefaultToolkit();
screenDims = tk.getScreenSize();
this.setLocation((screenDims.width - this.getWidth()) / 2, (screenDims.height - this.getHeight()) / 2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.pack();
this.setVisible(true);
}
public static void downloadExecutable(String str) {
url = null;
try {
url = new URL("http://pegr-converter.com/download/test.jpg");
} catch (MalformedURLException exc) {
JOptionPane.showMessageDialog(null, "Unexpected exception: " + exc.getMessage());
return;
}
if (url != null) {
String[] options = { "OK", "Change", "Cancel" };
int response = JOptionPane.NO_OPTION;
File selectedFolder = new File(getDownloadDir());
File selectedLocation = new File(selectedFolder, str + ".jpg");
while (response == JOptionPane.NO_OPTION) {
selectedLocation = new File(selectedFolder, str + ".jpg");
String msgStr = str + ".jpg will be downloaded to the following location:\n"
+ selectedLocation.toPath();
response = JOptionPane.showOptionDialog(null, msgStr, "Pegr input needed",
JOptionPane.YES_NO_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, options, options[0]);
if (response == JOptionPane.NO_OPTION) {
// Prompt for file selection.
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
fileChooser.setCurrentDirectory(selectedFolder);
fileChooser.showOpenDialog(null);
selectedFolder = fileChooser.getSelectedFile();
}
}
if (response == JOptionPane.YES_OPTION) {
int size = 0;
URLConnection conn;
try {
conn = url.openConnection();
size = conn.getContentLength();
} catch (IOException exc) {
System.out.println(exc.getMessage());
}
//System.out.println("javax.swing.SwingUtilities.isEventDispatchThread=" + javax.swing.SwingUtilities.isEventDispatchThread());
File destination = new File(selectedFolder, str + ".jpg");
status = new ProgressBar("Downloading " + str + ".jpg", destination, size);
SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>() {
@Override
protected Void doInBackground() throws Exception {
try {
FileUtils.copyURLToFile(url, destination, 10000, 300000);
} catch (IOException exc) {
JOptionPane.showMessageDialog(null, "Download failed.");
}
return null;
}
public void done() {
status.close();
}
};
worker.execute();
}
}
}
public static String getDownloadDir() {
String home = System.getProperty("user.home");
File downloadDir = new File(home + "/Downloads/");
if (downloadDir.exists() && !downloadDir.isDirectory()) {
return home;
} else {
downloadDir = new File(downloadDir + "/");
if ((downloadDir.exists() && downloadDir.isDirectory()) || downloadDir.mkdirs()) {
return downloadDir.getPath();
} else {
return home;
}
}
}
@Override
public void actionPerformed(ActionEvent arg0) {
downloadExecutable("test");
}
}