URLMonitorPanel.java Source code

Introduction

Here is the source code for URLMonitorPanel.java

Source

/*
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);
        }
    }
}