How can I show a progress bar while reading a file?

Scott Stanchfield

Here's a simple example of monitoring file read progress

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.FileInputStream;
import java.io.InputStream;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.ProgressMonitorInputStream;

public class Test {
  public static void main(String[] args) {
    // create a test frame with a "press me" button
    final JFrame f = new JFrame("Sample");
    f.getContentPane().setLayout(new FlowLayout());
    JButton b = new JButton("Press me");
    f.getContentPane().add(b);
    f.pack();

    // set up the file read action
    b.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        // when button is pressed, start a new thread
        //   to read the file. A new thread is needed because we
        //   need to free the GUI update thread to paint the
        //   progress monitor
        new Thread() {
          public void run() {
            try {
              // open the file, wrapping it in a ProgressMonitorInputStream
              InputStream in = new FileInputStream("c:Bigfile.bin");
              ProgressMonitorInputStream pm = 
                  new ProgressMonitorInputStream(f,"Reading the big file",in);
              // read the file. If it's taking too long, the progress
              //   monitor will appear. The amount of time is roughly
              //   1/100th of the estimated read time (based on how long
              //   it took to read the first 1/100th of the file.)
              //   Note that by default, the dialog won't appear unless
              //   the overall estimate is over 2 seconds.
              int c;
              while((c=pm.read()) != -1) {
                // do something
              }
              pm.close(); // needs better error handling, of course...
            }
            catch(Exception ex) {
              ex.printStackTrace();
            }
          }
        }.start();
      }});  
  
    // display the frame
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
  }
}
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