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Appendix: Source code listings"></td></tr><tr><td bgcolor="ffffff" width="15">&nbsp;</td><td bgcolor="ffffff" width="12">&nbsp;</td><td valign="top" align="left" bgcolor="ffffff" width="*"><p><br x="7"><table cellspacing="0" cellpadding="0" border="0"><tr><td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>Server.java</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>    page 1 of 4</nobr></font></td></tr></table><br x="7"><br x="7"></p><font size="2" face="Verdana, Arial, Helvetica"><pre><code style="font-family: Courier New, Courier, monospace; font-size: 12">
// $Id$

import java.io.*;
import java.net.*;
import java.util.*;

public class Server
{
  // The ServerSocket we'll use for accepting new connections
  private ServerSocket ss;

  // A mapping from sockets to DataOutputStreams.  This will
  // help us avoid having to create a DataOutputStream each time
  // we want to write to a stream.
  private Hashtable outputStreams = new Hashtable();

  // Constructor and while-accept loop all in one.
  public Server( int port ) throws IOException {

    // All we have to do is listen
    listen( port );
  }

  private void listen( int port ) throws IOException {

    // Create the ServerSocket
    ss = new ServerSocket( port );

    // Tell the world we're ready to go
    System.out.println( "Listening on "+ss );

    // Keep accepting connections forever
    while (true) {

      // Grab the next incoming connection
      Socket s = ss.accept();

      // Tell the world we've got it
      System.out.println( "Connection from "+s );

      // Create a DataOutputStream for writing data to the
      // other side
      DataOutputStream dout = new DataOutputStream( s.getOutputStream() );

      // Save this stream so we don't need to make it again
      outputStreams.put( s, dout );

      // Create a new thread for this connection, and then forget
      // about it
      new ServerThread( this, s );
    }
  }

  // Get an enumeration of all the OutputStreams, one for each client
  // connected to us
  Enumeration getOutputStreams() {
    return outputStreams.elements();
  }

  // Send a message to all clients (utility routine)
  void sendToAll( String message ) {

    // We synchronize on this because another thread might be
    // calling removeConnection() and this would screw us up
    // as we tried to walk through the list
    synchronized( outputStreams ) {

      // For each client ...
      for (Enumeration e = getOutputStreams(); e.hasMoreElements(); ) {

        // ... get the output stream ...
        DataOutputStream dout = (DataOutputStream)e.nextElement();

        // ... and send the message
        try {
          dout.writeUTF( message );
        } catch( IOException ie ) { System.out.println( ie ); }
      }
    }
  }

  // Remove a socket, and it's corresponding output stream, from our
  // list.  This is usually called by a connection thread that has
  // discovered that the connectin to the client is dead.
  void removeConnection( Socket s ) {

    // Synchronize so we don't mess up sendToAll() while it walks
    // down the list of all output streamsa
    synchronized( outputStreams ) {

      // Tell the world
      System.out.println( "Removing connection to "+s );

      // Remove it from our hashtable/list
      outputStreams.remove( s );

      // Make sure it's closed
      try {
        s.close();
      } catch( IOException ie ) {
        System.out.println( "Error closing "+s );
        ie.printStackTrace();
      }
    }
  }

  // Main routine
  // Usage: java Server &lt;port&gt;
  static public void main( String args[] ) throws Exception {

    // Get the port # from the command line
    int port = Integer.parseInt( args[0] );

    // Create a Server object, which will automatically begin
    // accepting connections.
    new Server( port );
  }
}

		</code></pre><br x="7"></font></td></tr></table><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD background="../i/sw-gold.gif"><a border="0" href="index.html" onMouseOver="iOver('topmain'); iOver('bottommain'); self.status=mainblurb; return true;" onMouseOut="iOut('topmain'); iOut('bottommain'); self.status=''; return true;"><img alt="Main menu" border="0" src="../i/main.gif" name="bottommain"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topsection'); iOver('bottomsection'); self.status=sectionblurb; return true;" onMouseOut="iOut('topsection'); iOut('bottomsection'); self.status=''; return true;" href="index12.html"><img alt="Section menu" border="0" src="../i/section.gif" name="bottomsection"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topfeedback'); iOver('bottomfeedback'); self.status=feedbackblurb; return true;" onMouseOut="iOut('topfeedback'); iOut('bottomfeedback'); self.status=''; return true;" href="j-chat-11-3.html"><img alt="Give feedback on this tutorial" border="0" src="../i/feedback.gif" name="bottomfeedback"></a></TD><TD width="100%" background="../i/sw-gold.gif"><img src="http://www.ibm.com/i/c.gif"></TD><TD background="../i/sw-gold.gif"><img border="0" src="../i/xprevious.gif"></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topnext'); iOver('bottomnext'); self.status=nextblurb; return true;" onMouseOut="iOut('topnext'); iOut('bottomnext'); self.status=''; return true;" href="j-chat-12-2.html"><img alt="Next" border="0" src="../i/next.gif" name="bottomnext"></a></TD></TR><TR><TD width="150" height="1" bgcolor="#000000" colspan="6"><IMG alt="" height="1" width="150" src="http://www.ibm.com/i/c.gif"></TD></TR></TABLE><TABLE cellpadding="0" cellspacing="0" border="0"><TR><TD width="182"><TABLE cellpadding="0" cellspacing="0" border="0" width="182"><TR bgcolor="#000000"><TD align="center" width="60" class="mast"><a style="text-decoration: none; color: #ffffff;" class="nav" href="http://www.ibm.com/privacy/"><font face="Arial, Verdana" size="2">Privacy</font></a></TD><TD width="1" bgcolor="#959595"><img alt="" border="0" height="20" width="1" src="http://www.ibm.com/i/c.gif"></TD><TD align="center" width="60" class="mast"><a style="text-decoration: none; color: #ffffff;" class="nav" href="http://www.ibm.com/legal/"><font face="Arial, Verdana" size="2">Legal</font></a></TD><TD width="1" bgcolor="#959595"><img alt="" border="0" height="20" width="1" src="http://www.ibm.com/i/c.gif"></TD><TD align="center" width="60" class="mast"><a style="text-decoration: none; color: #ffffff;" class="nav" href="http://www.ibm.com/contact/"><font face="Arial, Verdana" size="2">Contact</font></a></TD><TD width="1" bgcolor="#959595"><img alt="" border="0" height="21" width="1" src="http://www.ibm.com/i/c.gif"></TD></TR><TR bgcolor="#ffffff"><TD><img alt="" border="0" height="1" width="1" src="http://www.ibm.com/i/c.gif"></TD></TR></TABLE></TD><TD width="100%"><TABLE cellpadding="0" cellspacing="0" border="0" width="100%"><TR height="21" bgcolor="#000000"><TD><img alt="" border="0" height="21" width="1" src="http://www.ibm.com/i/c.gif"></TD></TR><TR bgcolor="#ffffff"><TD><img alt="" border="0" height="1" width="1" src="http://www.ibm.com/i/c.gif"></TD></TR></TABLE></TD></TR></TABLE></body></html>