Check if the specified address is within the required subnet

      
/*
 * Copyright (C) 2006-2008 Alfresco Software Limited.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 * As a special exception to the terms and conditions of version 2.0 of 
 * the GPL, you may redistribute this Program in connection with Free/Libre 
 * and Open Source Software ("FLOSS") applications as described in Alfresco's 
 * FLOSS exception.  You should have recieved a copy of the text describing 
 * the FLOSS exception, and it is also available here: 
 * http://www.alfresco.com/legal/licensing"
 */

//package net.gqu.utils;

import java.util.StringTokenizer;

/**
 * TCP/IP Address Utility Class
 *
 * @author gkspencer
 */
public class IPAddress {


  /**
   * Check if the specified address is within the required subnet
   * 
   * @param ipaddr String
   * @param subnet String
   * @param mask String
   * @return boolean
   */
  public final static boolean isInSubnet(String ipaddr, String subnet, String mask) {
    
    //  Convert the addresses to integer values
    
    int ipaddrInt = parseNumericAddress(ipaddr);
    if ( ipaddrInt == 0)
      return false;
      
    int subnetInt = parseNumericAddress(subnet);
    if ( subnetInt == 0)
      return false;
      
    int maskInt = parseNumericAddress(mask);
    if ( maskInt == 0)
      return false;
      
    //  Check if the address is part of the subnet
    
    if (( ipaddrInt & maskInt) == subnetInt)
      return true;
    return false;  
  }
  /**
   * Check if the specified address is a valid numeric TCP/IP address and return as an integer value
   * 
   * @param ipaddr String
   * @return int
   */
  public final static int parseNumericAddress(String ipaddr) {
  
    //  Check if the string is valid
    
    if ( ipaddr == null || ipaddr.length() < 7 || ipaddr.length() > 15)
      return 0;
      
    //  Check the address string, should be n.n.n.n format
    
    StringTokenizer token = new StringTokenizer(ipaddr,".");
    if ( token.countTokens() != 4)
      return 0;

    int ipInt = 0;
    
    while ( token.hasMoreTokens()) {
      
      //  Get the current token and convert to an integer value
      
      String ipNum = token.nextToken();
      
      try {
        
        //  Validate the current address part
        
        int ipVal = Integer.valueOf(ipNum).intValue();
        if ( ipVal < 0 || ipVal > 255)
          return 0;
          
        //  Add to the integer address
        
        ipInt = (ipInt << 8) + ipVal;
      }
      catch (NumberFormatException ex) {
        return 0;
      }
    }
    
    //  Return the integer address
    
    return ipInt;
  }


}

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Check if the specified address is within the required subnet : IP Address « Network Protocol « Java

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