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Who.javaAPI DocExample3699Sat Jun 02 02:44:22 BST 2001None

Who

public class Who extends Applet implements ActionListener, Runnable
This applet uses the connects to the "finger" server on the host it was served from to determine who is currently logged on. Because it is an untrusted applet, it can only connect to the host from which it came. Since web servers do not usually run finger servers themselves, this applet will often be used in conjunction with a proxy server, to serve it from some other host that does run a finger server.

Fields Summary
Button
who
Constructors Summary
Methods Summary
public voidactionPerformed(java.awt.event.ActionEvent e)
When the button is clicked, start a thread that will connect to the finger server and display who is logged on

    if (e.getActionCommand().equals("who")) new Thread(this).start();
public voidinit()
The init method just creates a button to display in the applet. When the user clicks the button, we'll check who is logged on.

    who = new Button("Who?");
    who.setFont(new Font("SansSerif", Font.PLAIN, 14));
    who.addActionListener(this);
    who.setActionCommand("who");
    this.add(who);
public voidrun()
This is the method that does the networking and displays the results. It is implemented as the body of a separate thread because it might take some time to complete, and applet methods need to return promptly.

    // Disable the button so we don't get multiple queries at once...
    who.setEnabled(false);

    // Create a window to display the output in
    Frame f = new CloseableFrame("Who's Logged On: Connecting...");
    TextArea t = new TextArea(10, 80);
    t.setFont(new Font("MonoSpaced", Font.PLAIN, 10));
    f.add(t, "Center");
    f.pack();
    f.show();

    // Find out  who's logged on
    Socket s = null;
    PrintWriter out = null;
    BufferedReader in = null;
    try {
      // Connect to port 79 (the standard finger port) on the host
      // that the applet was loaded from.
      String hostname = this.getCodeBase().getHost();
      s = new Socket(hostname, 79);
      // Set up the streams
      out = new PrintWriter(new OutputStreamWriter(s.getOutputStream()));
      in = new BufferedReader(new InputStreamReader(s.getInputStream()));

      // Send a blank line to the finger server, telling it that we want
      // a listing of everyone logged on instead of information about an
      // individual user.
      out.println();
      out.flush();    // Send it now!

      // Now read the server's response and display it in the textarea
      String line;
      while((line = in.readLine()) != null) {
        t.append(line);
        t.append("\n");
      }
      f.setTitle("Who's Logged On: " + hostname);
    }
    // If something goes wrong, we'll just display the exception message
    catch (IOException e) { 
      t.append(e.toString()); 
      f.setTitle("Who's Logged On: Error");
    }
    // And finally, don't forget to close the streams!
    finally { try {in.close(); out.close(); s.close();} catch(Exception e){} }
    
    // And enable the button again
    who.setEnabled(true);