/* * Copyright (c) 2000 David Flanagan.  All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd Edition. * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied. * You may study, use, and modify it for any non-commercial purpose. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book (recommended), * visit http://www.davidflanagan.com/javaexamples2. */package com.davidflanagan.examples.net;import java.applet.*;import java.awt.*;import java.awt.event.*;import java.io.*;import java.net.*;/**  * This applet 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. **/public class Who extends Applet implements ActionListener, Runnable {    Button who;  // The button in the applet    /**     * 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.     **/    public void init() {        who = new Button("Who?");        who.setFont(new Font("SansSerif", Font.PLAIN, 14));        who.addActionListener(this);        this.add(who);    }        /**      * When the button is clicked, start a thread that will connect to     * the finger server and display who is logged on     **/    public void actionPerformed(ActionEvent e) { new Thread(this).start(); }        /**     * 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.     **/    public void run() {        // 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 Frame("Who's Logged On: Connecting...");	f.addWindowListener(new WindowAdapter() {		public void windowClosing(WindowEvent e) {		    ((Frame)e.getSource()).dispose();		}	    });        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.print("\n");            out.flush();    // Send it now!	                // Now read the server's response and display it in the textarea	    // The server should send lines terminated with \n.  The 	    // readLine() method will detect these lines, even when running	    // on a Mac that terminates lines with \r            String line;            while((line = in.readLine()) != null) {                t.append(line);                t.append("\n");            }	    // Update the window title to indicate we're finished            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);    }}