import java.net.*;import java.io.*;import java.util.*;/***Thread to scan TCP port on host**Copyright (C) 2003 Tom Salmon tom@slashtom.org**This program is free software; you can redistribute it and/ormodify it under the terms of the GNU General Public Licenseas published by the Free Software Foundation; version 2.This program is distributed in the hope that it will be useful,but WITHOUT ANY WARRANTY; without even the implied warranty ofMERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See theGNU General Public License for more details.You should have received a copy of the GNU General Public Licensealong with this program; if not, write to the Free SoftwareFoundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.**@author Tom Salmon tom@slashtom.org*@version 0.3.1*/public class ScanTCP extends Observable implements Runnable {	private InetAddress IP;	private int port;	private int timesDropped = 0;	private int timesClosed = 0;	private static int SOCKET_TIMEOUT = 2000;	private static int MAX_TIMES_DROPPED = 3;	private static int MAX_TIMES_CLOSED = 2;	/*	*Constructs new thread to Scan host on TCP port	*@param InetAddress the IP address of host to scan	*@param int port number to scan	*/	public ScanTCP(InetAddress IP, int port){		this.IP = IP;		this.port = port;		// if we are running on Windows, increase timeout and no. of retries		if (System.getProperty("os.name").startsWith("Windows")){			this.SOCKET_TIMEOUT = 2500;			this.MAX_TIMES_DROPPED = 4;			this.MAX_TIMES_CLOSED = 3;		}	}	/**	*Returns the IP address being scanned	*/	public InetAddress getIP(){		return IP;	}	/**	*Return the port being scanned	*/	public int getPort(){		return port;	}	/**	*Scans host/port using the TCP protocol	*/	public void run() {        try{			String portsStatus = this.scanTCP();			setChanged();			notifyObservers(portsStatus);        }        catch(NoRouteToHostException e){			setChanged();            notifyObservers("null"); //null to signify error contacting host			return;        }	}    /**    *Scans single port using specified TCP hoost/port    *@return String - either OPEN CLOSED DROPPED    */    public String scanTCP() throws NoRouteToHostException{        try{            Socket s = new Socket();			//set the socket to timeout, multiply the timeout by number of retry            s.connect(new InetSocketAddress(IP, port), 					  this.SOCKET_TIMEOUT * ((timesDropped | timesClosed)+1));            s.close();        }        catch(NoRouteToHostException e){            throw e; //throw to calling        }        catch(SocketTimeoutException e){			/*			* Sometimes a socket times out in error (due to intensive scanning)			*check again, to make sure			*/			if (this.timesDropped < this.MAX_TIMES_DROPPED){				this.timesDropped++;				try{					Thread.sleep(2500); // wait before trying again				}				catch(Exception f){				}				// scan again!				return this.scanTCP();			}			else{            	return "DROPPED";			}        }        catch(IOException e){			if (this.timesClosed < this.MAX_TIMES_CLOSED){				this.timesClosed++;				try{					Thread.sleep(2500);				}				catch(Exception f){				}				return this.scanTCP();			}			else{            	return "CLOSED";			}        }        //if got this far, is opem        return "OPEN";    }}