Mega Code Archive
Task Scheduling
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/*
Java Threads, 3rd Edition
By Scott Oaks, Henry Wong
3rd Edition September 2004
ISBN: 0-596-00782-5
*/
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Timer;
import java.util.TimerTask;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class URLMonitorPanel extends JPanel implements URLPingTask.URLUpdate {
Timer timer;
URL url;
URLPingTask task;
JPanel status;
JButton startButton, stopButton;
public URLMonitorPanel(String url, Timer t) throws MalformedURLException {
setLayout(new BorderLayout());
timer = t;
this.url = new URL(url);
add(new JLabel(url), BorderLayout.CENTER);
JPanel temp = new JPanel();
status = new JPanel();
status.setSize(20, 20);
temp.add(status);
startButton = new JButton("Start");
startButton.setEnabled(false);
startButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
makeTask();
startButton.setEnabled(false);
stopButton.setEnabled(true);
}
});
stopButton = new JButton("Stop");
stopButton.setEnabled(true);
stopButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
task.cancel();
startButton.setEnabled(true);
stopButton.setEnabled(false);
}
});
temp.add(startButton);
temp.add(stopButton);
add(temp, BorderLayout.EAST);
makeTask();
}
private void makeTask() {
task = new URLPingTask(url, this);
timer.schedule(task, 0L, 5000L);
}
public void isAlive(final boolean b) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
status.setBackground(b ? Color.GREEN : Color.RED);
status.repaint();
}
});
}
public static void main(String[] args) throws Exception {
JFrame frame = new JFrame("URL Monitor");
Container c = frame.getContentPane();
c.setLayout(new BoxLayout(c, BoxLayout.Y_AXIS));
Timer t = new Timer();
String[] u = new String[]{"http://www.rntsoft.com","http://www.rntsoft.com"};
for (int i = 0; i < u.length; i++) {
c.add(new URLMonitorPanel(u[i], t));
}
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent evt) {
System.exit(0);
}
});
frame.pack();
frame.show();
}
}
class URLPingTask extends TimerTask {
public interface URLUpdate {
public void isAlive(boolean b);
}
URL url;
URLUpdate updater;
public URLPingTask(URL url) {
this(url, null);
}
public URLPingTask(URL url, URLUpdate uu) {
this.url = url;
updater = uu;
}
public void run() {
if (System.currentTimeMillis() - scheduledExecutionTime() > 5000) {
// Let the next task do it
return;
}
try {
HttpURLConnection huc = (HttpURLConnection) url.openConnection();
huc.setConnectTimeout(1000);
huc.setReadTimeout(1000);
int code = huc.getResponseCode();
if (updater != null)
updater.isAlive(true);
} catch (Exception e) {
if (updater != null)
updater.isAlive(false);
}
}
}
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