Source Code : Task Scheduling

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Task Scheduling

 
/*
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.java2s.com","http://www.java2s.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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