When performing a time consuming task usually we prefer another worker thread since the time consuming activity should not block the GUI events.
Java has a special class called SwingWorker to do such background activities by keeping GUI responsive.
SwingWorker provides a number of communication and control features:
Here I will give an example for Swingworker with some background activity having a progress bar to show it’s status.
The following example is a file locker application by which we can lock a file.Here we we have used basic XOR encryption with ‘1’ to encrypt the file, to unlock a file encrypt already locked file one more time.
Mainframe.java
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Locale;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.JTextField;
import javax.swing.filechooser.FileFilter;
public class Mainframe extends JFrame implements ActionListener {
public void createGUI(){
setTitle("File Locker");
fileSelectBtn = new JButton("::");
fileSelectBtn.addActionListener(this);
pb = new JProgressBar(0, 100);
// pb.setValue(0);
pb.setIndeterminate(false);
pb.setStringPainted(true);
pb.setVisible(true);
JPanel panel = new JPanel();
label = new JLabel("File");
textField = new JTextField(15);
// textField.setEditable(false);
panel.add(label);
panel.add(textField);
panel.add(fileSelectBtn);
JPanel panel1 = new JPanel();
panel1.setLayout(new BorderLayout());
panel1.add(panel, BorderLayout.NORTH);
JPanel panel2 = new JPanel();
encryptBtn = new JButton("Encrypt");
encryptBtn.addActionListener(this);
panel2.add(encryptBtn);
panel2.add(pb);
panel1.add(panel2, BorderLayout.CENTER);
panel1.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
setContentPane(panel1);
pack();
setResizable(false);
setSize(400, 150);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void actionPerformed(ActionEvent e) {
if(e.getSource().equals(fileSelectBtn)){
JFileChooser filechooser = new JFileChooser(".");
if (filechooser.showOpenDialog(this) == JFileChooser.APPROVE_OPTION)
{
selectedFile = filechooser.getSelectedFile();
textField.setText(selectedFile.getAbsolutePath());
textField.setToolTipText(selectedFile.getAbsolutePath());
}
}else if(e.getSource().equals(encryptBtn)){
FileInputStream fin = null;
try {
// create FileInputStream object
if(selectedFile == null){
JOptionPane.showMessageDialog(this, "Please select any file.", "Error Message", JOptionPane.INFORMATION_MESSAGE);
return;
}
fin = new FileInputStream(selectedFile);
long length = selectedFile.length();
byte fileContent[] = new byte[(int)selectedFile.length()];
// Reads up to certain bytes of data from this input stream into an array of bytes.
fin.read(fileContent);
fin.close();
FileEncryptPerformer actionPerform = new FileEncryptPerformer(this, fileContent,
selectedFile.getAbsolutePath(),
pb);
actionPerform.execute();
}
catch (FileNotFoundException ex) {
JOptionPane.showMessageDialog(this, "File not found.", "Error Message", JOptionPane.INFORMATION_MESSAGE);
System.out.println("File not found" + ex);
}
catch (IOException ioe) {
JOptionPane.showMessageDialog(this, "Exception while reading file.", "Error Message", JOptionPane.INFORMATION_MESSAGE);
System.out.println("Exception while reading file " + ioe);
}
finally {
// close the streams using close method
try {
if (fin != null) {
fin.close();
}
}
catch (IOException ioe) {
JOptionPane.showMessageDialog(this, "Error while closing stream.", "Error Message", JOptionPane.INFORMATION_MESSAGE);
System.out.println("Error while closing stream: " + ioe);
}
}
}
}
private JButton fileSelectBtn;
private JButton encryptBtn;
private JProgressBar pb;
JTextField textField;
JLabel label;
File selectedFile;
}
FileEncryptPerformer.java
import java.awt.Cursor;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.swing.JOptionPane;
import javax.swing.JProgressBar;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;
class FileEncryptPerformer extends SwingWorker {
JProgressBar fProgressBar;
private byte fileContent[];
private String fileName;
Mainframe mainFrame ;
public FileEncryptPerformer(Mainframe mainFrame, byte fileContent[],String fileName, JProgressBar progressBar) {
this.mainFrame = mainFrame;
this.fileContent = fileContent;
this.fileName = fileName;
this.fProgressBar = progressBar;
}
protected String doInBackground() throws Exception {
mainFrame.setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
setStatusText(0);
encrypt();
writeToFile();
return "Finished";
}
private void writeToFile() throws IOException {
BufferedOutputStream bos = null;
try {
//create an object of FileOutputStream
FileOutputStream fos = new FileOutputStream(new File(fileName));
//create an object of BufferedOutputStream
bos = new BufferedOutputStream(fos);
bos.write(fileContent);
}catch (FileNotFoundException e) {
if(bos !=null)
bos.close();
done();
JOptionPane.showMessageDialog(mainFrame, "File not found.", "Error Message", JOptionPane.INFORMATION_MESSAGE);
return ;
}
catch (IOException e) {
if(bos !=null)
bos.close();
done();
JOptionPane.showMessageDialog(mainFrame, "Exception while reading file.", "Error Message", JOptionPane.INFORMATION_MESSAGE);
return ;
}
}
protected void done() {
mainFrame.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
setStatusText(100);
}
public void encrypt() {
int stepSize = fileContent.length/100;
for ( int i = 0; i < fileContent.length; i++) {
fileContent[i] = (byte) (fileContent[i] ^ (byte)1);
float stepCount = (float)i/fileContent.length;
final int count = (int)(stepCount*100);
//fProgressBar.setValue(count);
setStatusText(count);
}
}
public void setStatusText(final int status) {
SwingUtilities.invokeLater(new Runnable(){
//@Override
public void run() {
fProgressBar.setValue(status);
}
});
}
}
following class is the main class.
SwingProgressBar.java
public class SwingProgressBar{
public static void main(String[] args) {
Mainframe frame = new Mainframe();
frame.createGUI();
}
}
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