Mega Code Archive
This program demonstrates a swing-worker thread that runs a potentially time-consuming task
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/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.List;
import java.util.Scanner;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
/**
* This program demonstrates a worker thread that runs a potentially
* time-consuming task.
*
* @version 1.1 2007-05-18
* @author Cay Horstmann
*/
public class SwingWorkerTest {
public static void main(String[] args) throws Exception {
EventQueue.invokeLater(new Runnable() {
public void run() {
JFrame frame = new SwingWorkerFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
});
}
}
/**
* This frame has a text area to show the contents of a text file, a menu to
* open a file and cancel the opening process, and a status line to show the
* file loading progress.
*/
class SwingWorkerFrame extends JFrame {
public SwingWorkerFrame() {
chooser = new JFileChooser();
chooser.setCurrentDirectory(new File("."));
textArea = new JTextArea();
add(new JScrollPane(textArea));
setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
statusLine = new JLabel(" ");
add(statusLine, BorderLayout.SOUTH);
JMenuBar menuBar = new JMenuBar();
setJMenuBar(menuBar);
JMenu menu = new JMenu("File");
menuBar.add(menu);
openItem = new JMenuItem("Open");
menu.add(openItem);
openItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
// show file chooser dialog
int result = chooser.showOpenDialog(null);
// if file selected, set it as icon of the label
if (result == JFileChooser.APPROVE_OPTION) {
textArea.setText("");
openItem.setEnabled(false);
textReader = new TextReader(chooser.getSelectedFile());
textReader.execute();
cancelItem.setEnabled(true);
}
}
});
cancelItem = new JMenuItem("Cancel");
menu.add(cancelItem);
cancelItem.setEnabled(false);
cancelItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
textReader.cancel(true);
}
});
}
private class ProgressData {
public int number;
public String line;
}
private class TextReader extends SwingWorker<StringBuilder, ProgressData> {
public TextReader(File file) {
this.file = file;
}
// the following method executes in the worker thread; it doesn't touch
// Swing components
@Override
public StringBuilder doInBackground() throws IOException, InterruptedException {
int lineNumber = 0;
Scanner in = new Scanner(new FileInputStream(file));
while (in.hasNextLine()) {
String line = in.nextLine();
lineNumber++;
text.append(line);
text.append("\n");
ProgressData data = new ProgressData();
data.number = lineNumber;
data.line = line;
publish(data);
Thread.sleep(1); // to test cancellation; no need to do this in your
// programs
}
return text;
}
// the following methods execute in the event dispatch thread
@Override
public void process(List<ProgressData> data) {
if (isCancelled())
return;
StringBuilder b = new StringBuilder();
statusLine.setText("" + data.get(data.size() - 1).number);
for (ProgressData d : data) {
b.append(d.line);
b.append("\n");
}
textArea.append(b.toString());
}
@Override
public void done() {
try {
StringBuilder result = get();
textArea.setText(result.toString());
statusLine.setText("Done");
} catch (InterruptedException ex) {
} catch (CancellationException ex) {
textArea.setText("");
statusLine.setText("Cancelled");
} catch (ExecutionException ex) {
statusLine.setText("" + ex.getCause());
}
cancelItem.setEnabled(false);
openItem.setEnabled(true);
}
private File file;
private StringBuilder text = new StringBuilder();
};
private JFileChooser chooser;
private JTextArea textArea;
private JLabel statusLine;
private JMenuItem openItem;
private JMenuItem cancelItem;
private SwingWorker<StringBuilder, ProgressData> textReader;
public static final int DEFAULT_WIDTH = 450;
public static final int DEFAULT_HEIGHT = 350;
}
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