Java/Network Protocol/IP Address

A class that performs some subnet calculations given a network address and a subnet mask.

  
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
 * A class that performs some subnet calculations given a network address and a subnet mask. 
 * @see http://www.faqs.org/rfcs/rfc1519.html
 * @author <rwinston@apache.org>
 * @since 2.0
 */
public class SubnetUtils {
    private static final String IP_ADDRESS = "(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})";
    private static final String SLASH_FORMAT = IP_ADDRESS + "/(\\d{1,3})";
    private static final Pattern addressPattern = Pattern.rupile(IP_ADDRESS);
    private static final Pattern cidrPattern = Pattern.rupile(SLASH_FORMAT);
    private static final int NBITS = 32;
    private int netmask = 0;
    private int address = 0;
    private int network = 0;
    private int broadcast = 0;
    /**
     * Constructor that takes a CIDR-notation string, e.g. "192.168.0.1/16"
     * @param cidrNotation A CIDR-notation string, e.g. "192.168.0.1/16"
     */
    public SubnetUtils(String cidrNotation) {
        calculate(cidrNotation);
    }
    /**
     * Constructor that takes two dotted decimal addresses. 
     * @param address An IP address, e.g. "192.168.0.1"
     * @param mask A dotted decimal netmask e.g. "255.255.0.0"
     */
    public SubnetUtils(String address, String mask) {
        calculate(toCidrNotation(address, mask));
    }
    /**
     * Convenience container for subnet summary information.
     *
     */
    public final class SubnetInfo {
        private SubnetInfo() {}
        private int netmask()       { return netmask; }
        private int network()       { return network; }
        private int address()       { return address; }
        private int broadcast()     { return broadcast; }
        private int low()           { return network() + 1; }
        private int high()          { return broadcast() - 1; }
        public boolean isInRange(String address)    { return isInRange(toInteger(address)); }
        private boolean isInRange(int address)      { return ((address-low()) <= (high()-low())); }
        public String getBroadcastAddress()         { return format(toArray(broadcast())); }
        public String getNetworkAddress()           { return format(toArray(network())); }
        public String getNetmask()                  { return format(toArray(netmask())); }
        public String getAddress()                  { return format(toArray(address())); }
        public String getLowAddress()               { return format(toArray(low())); }
        public String getHighAddress()              { return format(toArray(high())); }
        public int getAddressCount()                { return (broadcast() - low()); }
        public int asInteger(String address)        { return toInteger(address); }
        
        public String getCidrSignature() { 
            return toCidrNotation(
                    format(toArray(address())), 
                    format(toArray(netmask()))
            );
        }
        
        public String[] getAllAddresses() { 
            String[] addresses = new String[getAddressCount()];
            for (int add = low(), j=0; add <= high(); ++add, ++j) {
                addresses[j] = format(toArray(add));
            }
            return addresses;
        }
    }
    /**
     * Return a {@link SubnetInfo} instance that contains subnet-specific statistics
     * @return
     */
    public final SubnetInfo getInfo() { return new SubnetInfo(); }
    /*
     * Initialize the internal fields from the supplied CIDR mask
     */
    private void calculate(String mask) {
        Matcher matcher = cidrPattern.matcher(mask);
        if (matcher.matches()) {
            address = matchAddress(matcher);
            /* Create a binary netmask from the number of bits specification /x */
            int cidrPart = rangeCheck(Integer.parseInt(matcher.group(5)), 0, NBITS-1);
            for (int j = 0; j < cidrPart; ++j) {
                netmask |= (1 << 31-j);
            }
            /* Calculate base network address */
            network = (address & netmask);
            /* Calculate broadcast address */
            broadcast = network | ~(netmask);
        }
        else 
            throw new IllegalArgumentException("Could not parse [" + mask + "]");
    }
    /*
     * Convert a dotted decimal format address to a packed integer format
     */
    private int toInteger(String address) {
        Matcher matcher = addressPattern.matcher(address);
        if (matcher.matches()) {
            return matchAddress(matcher);
        }
        else
            throw new IllegalArgumentException("Could not parse [" + address + "]");
    }
    /*
     * Convenience method to extract the components of a dotted decimal address and 
     * pack into an integer using a regex match
     */
    private int matchAddress(Matcher matcher) {
        int addr = 0;
        for (int i = 1; i <= 4; ++i) { 
            int n = (rangeCheck(Integer.parseInt(matcher.group(i)), 0, 255));
            addr |= ((n & 0xff) << 8*(4-i));
        }
        return addr;
    }
    /*
     * Convert a packed integer address into a 4-element array
     */
    private int[] toArray(int val) {
        int ret[] = new int[4];
        for (int j = 3; j >= 0; --j)
            ret[j] |= ((val >>> 8*(3-j)) & (0xff));
        return ret;
    }
    /*
     * Convert a 4-element array into dotted decimal format
     */
    private String format(int[] octets) {
        StringBuilder str = new StringBuilder();
        for (int i =0; i < octets.length; ++i){
            str.append(octets[i]);
            if (i != octets.length - 1) {
                str.append("."); 
            }
        }
        return str.toString();
    }
    /*
     * Convenience function to check integer boundaries
     */
    private int rangeCheck(int value, int begin, int end) {
        if (value >= begin && value <= end)
            return value;
        throw new IllegalArgumentException("Value out of range: [" + value + "]");
    }
    /*
     * Count the number of 1-bits in a 32-bit integer using a divide-and-conquer strategy
     * see Hacker"s Delight section 5.1 
     */
    int pop(int x) {
        x = x - ((x >>> 1) & 0x55555555); 
        x = (x & 0x33333333) + ((x >>> 2) & 0x33333333); 
        x = (x + (x >>> 4)) & 0x0F0F0F0F; 
        x = x + (x >>> 8); 
        x = x + (x >>> 16); 
        return x & 0x0000003F; 
    } 
    /* Convert two dotted decimal addresses to a single xxx.xxx.xxx.xxx/yy format
     * by counting the 1-bit population in the mask address. (It may be better to count 
     * NBITS-#trailing zeroes for this case)
     */
    private String toCidrNotation(String addr, String mask) {
        return addr + "/" + pop(toInteger(mask));
    }
}

An nslookup clone in Java

   
import java.io.DataInputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
/**
 * An "nslookup" clone in Java.
 * 
 * @author Elliot Rusty Harold, O"Reilly & Associates
 */
public class JavaLookup {
  public static void main(String args[]) {
    if (args.length > 0) { // use command line
      for (int i = 0; i < args.length; i++) {
        lookup(args[i]);
      }
    } else {
      DataInputStream myInputStream = new DataInputStream(System.in);
      System.out
          .println("Enter names and IP addresses. Enter \"exit\" to quit.");
      while (true) {
        String s;
        try {
          s = myInputStream.readLine();
        } catch (IOException e) {
          break;
        }
        if (s.equals("exit"))
          break;
        if (s.equals("quit"))
          break;
        if (s.charAt(0) == "\004")
          break; // unix ^D
        lookup(s);
      }
    }
  } /* end main */
  private static void lookup(String s) {
    InetAddress thisComputer;
    byte[] address;
    // get the bytes of the IP address
    try {
      thisComputer = InetAddress.getByName(s);
      address = thisComputer.getAddress();
    } catch (UnknownHostException ue) {
      System.out.println("Cannot find host " + s);
      return;
    }
    if (isHostname(s)) {
      // Print the IP address
      for (int i = 0; i < address.length; i++) {
        int unsignedByte = address[i] < 0 ? address[i] + 256
            : address[i];
        System.out.print(unsignedByte + ".");
      }
      System.out.println();
    } else { // this is an IP address
      try {
        System.out.println(InetAddress.getByName(s));
      } catch (UnknownHostException e) {
        System.out.println("Could not lookup the address " + s);
      }
    }
  } // end lookup
  private static boolean isHostname(String s) {
    char[] ca = s.toCharArray();
    // if we see a character that is neither a digit nor a period
    // then s is probably a hostname
    for (int i = 0; i < ca.length; i++) {
      if (!Character.isDigit(ca[i])) {
        if (ca[i] != ".") {
          return true;
        }
      }
    }
    // Everything was either a digit or a period
    // so s looks like an IP address in dotted quad format
    return false;
  } // end isHostName
} // end javalookup

Convert a hostname to the equivalent IP address

   
import java.net.InetAddress;
import java.net.UnknownHostException;
public class GetIP {
  public static void main(String[] args) {
    InetAddress address = null;
    try {
      address = InetAddress.getByName("www.jexp.ru");
    } catch (UnknownHostException e) {
      System.exit(2);
    }
    System.out.println(address.getHostName() + "="
        + address.getHostAddress());
    System.exit(0);
  }
}

Determine the IP address and hostname of the local machine

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    InetAddress addr = InetAddress.getLocalHost();
    // Get IP Address
    byte[] ipAddr = addr.getAddress();
    // Get hostname
    String hostname = addr.getHostName();
  }
}

Display multiple IP addresses

     
import java.net.*;
public class GetAllIP {
  public static void main(String [] args) throws Exception {
    InetAddress[] addr = InetAddress.getAllByName("www.jexp.ru");
    for (int i=0;i<addr.length;i++)
      System.out.println(addr[i]);
    }
  }

Get all IP addresses

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] args) throws Exception {
    InetAddress[] addr = InetAddress.getAllByName(args[0]);
    for (int i = 0; i < addr.length; i++)
      System.out.println(addr[i]);
  }
}

Get canonical host name

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    byte[] ipAddr = new byte[] { 127, 0, 0, 1 };
    InetAddress addr = InetAddress.getByAddress(ipAddr);
    String hostnameCanonical = addr.getCanonicalHostName();
  }
}

Get hostname by a byte array containing the IP address

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    byte[] ipAddr = new byte[] { 127, 0, 0, 1 };
    InetAddress addr = InetAddress.getByAddress(ipAddr);
  }
}

Get IP

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] args) throws Exception {
    InetAddress address = null;
    if (args.length == 0) {
      System.out.println("usage: GetIP host");
      System.exit(1);
    }
    address = InetAddress.getByName(args[0]);
    System.out.println(address.getHostName() + "=" + address.getHostAddress());
    System.exit(0);
  }
}

Getting the Hostname of an IP Address

   

import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    // Get hostname by textual representation of IP address
    InetAddress addr = InetAddress.getByName("127.0.0.1");
  }
}

Getting the IP Address and Hostname of the Local Machine

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    InetAddress addr = InetAddress.getLocalHost();
    // Get IP Address
    byte[] ipAddr = addr.getAddress();
    // Get hostname
    String hostname = addr.getHostName();
  }
}

Looking for Port: 1024 -- 65536

   
import java.net.*;
import java.io.*;
public class lookForPorts2 {
  public static void main(String[] args) {
    Socket theSocket;
    String host = "localhost";
    if (args.length > 0) {
      host = args[0];
    }
    try {
      InetAddress theAddress = InetAddress.getByName(host);
      for (int i = 1024; i < 65536; i++) {
        try {
          System.out.println("Looking for port "+ i);
          theSocket = new Socket(theAddress, i);
          System.out.println("There is a server on port " + i + " of " + host);
        } catch (IOException e) {
          // must not be a server on this port
        }
      }
    } catch (UnknownHostException e) {
      System.err.println(e);
    }
  }
}

Looking for Ports: 0 -- 1024

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

public class lookForPorts {
  public static void main(String[] args) {
    
    Socket theSocket;
    String host = "localhost";
    if (args.length > 0) {
      host = args[0];
    }
    for (int i = 0; i < 1024; i++) {
      try {
        System.out.println("Looking for "+ i);
        theSocket = new Socket(host, i);
        System.out.println("There is a server on port " + i + " of " + host);
      }
      catch (UnknownHostException e) {
        System.err.println(e);
        break;
      }
      catch (IOException e) {
        // must not be a server on this port
      }
    }
  }
}

Looking for Port: start from 65535

   
import java.io.IOException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
public class lookForPorts3 {
  public static void main(String[] args) {
    Socket theSocket;
    String host = "localhost";
    if (args.length > 0) {
      host = args[0];
    }
    try {
      InetAddress theAddress = InetAddress.getByName(host);
      for (int i = 1; i <= 65535; i++) {
        try {
          theSocket = new Socket(host, i);
          System.out.println("There is a server on port " + i + " of " + host);
          theSocket.close();
        } catch (IOException e) {
          // must not be a server on this port
        }
      }
    } catch (UnknownHostException e) {
      System.err.println(e);
    }
  }
}

Looking Up the Address of a Host

   
import java.net.InetAddress;
import java.net.UnknownHostException;
public class DNSLookup {
  public static void main(String args[]) {
    try {
      InetAddress host;
      if (args.length == 0) {
        host = InetAddress.getLocalHost();
      } else {
        host = InetAddress.getByName(args[0]);
      }
      System.out.println("Host:"" + host.getHostName()
          + "" has address: " + host.getHostAddress());
      byte bytes[] = host.getAddress();
      int fourBytes[] = new int[bytes.length];
      for (int i = 0, n = bytes.length; i < n; i++) {
        fourBytes[i] = bytes[i] & 255;
      }
      System.out.println("\t" + fourBytes[0] + "." + fourBytes[1] + "."
          + fourBytes[2] + "." + fourBytes[3]);
    } catch (UnknownHostException e) {
      e.printStackTrace();
    }
  }
}

Perform Network Lookup with the InetAddress class

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] args) throws Exception{
    InetAddress inetHost = InetAddress.getByName("www.google.ru");
    String hostName = inetHost.getHostName();
    System.out.println(hostName);
    System.out.println(inetHost.getHostAddress());
  }
}

Report By Address

   
import java.net.InetAddress;
import java.net.NetworkInterface;
public class Main {
  static public void main(String args[]) throws Exception {
    InetAddress ia = InetAddress.getByName(args[0]);
    NetworkInterface ni = NetworkInterface.getByInetAddress(ia);
    System.out.println(ni);
  }
}

Resolves hostname and returns ip address as a string

 

// Copyright (c) 2003-2009, Jodd Team (jodd.org). All Rights Reserved.

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.URL;
import java.net.UnknownHostException;
/**
 * Network utilities.
 */
public class NetUtil {
  /**
   * Resolves hostname and returns ip address as a string.
   */
  public static String resolveHost(String hostname) {
    try {
      InetAddress addr = Inet4Address.getByName(hostname);
      byte[] ipAddr = addr.getAddress();
      StringBuilder ipAddrStr = new StringBuilder(15);
      for (int i = 0; i < ipAddr.length; i++) {
        if (i > 0) {
          ipAddrStr.append(".");
        }
        ipAddrStr.append(ipAddr[i] & 0xFF);
      }
      return ipAddrStr.toString();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }
  /**
   * Resolves string ip address and returns host name as a string.
   */
  public static String resolveIp(String ip) {
    try {
      InetAddress addr = InetAddress.getByName(ip);
      return addr.getHostName();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }
  /**
   * Resolves ip address and returns host name as a string.
   */
  public static String resolveIp(byte[] ip) {
    try {
      InetAddress addr = InetAddress.getByAddress(ip);
      return addr.getHostName();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }

}

Resolves ip address and returns host name as a string

 
// Copyright (c) 2003-2009, Jodd Team (jodd.org). All Rights Reserved.

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.URL;
import java.net.UnknownHostException;
/**
 * Network utilities.
 */
public class NetUtil {
  /**
   * Resolves hostname and returns ip address as a string.
   */
  public static String resolveHost(String hostname) {
    try {
      InetAddress addr = Inet4Address.getByName(hostname);
      byte[] ipAddr = addr.getAddress();
      StringBuilder ipAddrStr = new StringBuilder(15);
      for (int i = 0; i < ipAddr.length; i++) {
        if (i > 0) {
          ipAddrStr.append(".");
        }
        ipAddrStr.append(ipAddr[i] & 0xFF);
      }
      return ipAddrStr.toString();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }
  /**
   * Resolves string ip address and returns host name as a string.
   */
  public static String resolveIp(String ip) {
    try {
      InetAddress addr = InetAddress.getByName(ip);
      return addr.getHostName();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }
  /**
   * Resolves ip address and returns host name as a string.
   */
  public static String resolveIp(byte[] ip) {
    try {
      InetAddress addr = InetAddress.getByAddress(ip);
      return addr.getHostName();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }

}

Resolves string ip address and returns host name as a string

 
// Copyright (c) 2003-2009, Jodd Team (jodd.org). All Rights Reserved.

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.URL;
import java.net.UnknownHostException;
/**
 * Network utilities.
 */
public class NetUtil {
  /**
   * Resolves hostname and returns ip address as a string.
   */
  public static String resolveHost(String hostname) {
    try {
      InetAddress addr = Inet4Address.getByName(hostname);
      byte[] ipAddr = addr.getAddress();
      StringBuilder ipAddrStr = new StringBuilder(15);
      for (int i = 0; i < ipAddr.length; i++) {
        if (i > 0) {
          ipAddrStr.append(".");
        }
        ipAddrStr.append(ipAddr[i] & 0xFF);
      }
      return ipAddrStr.toString();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }
  /**
   * Resolves string ip address and returns host name as a string.
   */
  public static String resolveIp(String ip) {
    try {
      InetAddress addr = InetAddress.getByName(ip);
      return addr.getHostName();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }
  /**
   * Resolves ip address and returns host name as a string.
   */
  public static String resolveIp(byte[] ip) {
    try {
      InetAddress addr = InetAddress.getByAddress(ip);
      return addr.getHostName();
    } catch (UnknownHostException uhex) {
      return null;
    }
  }

}

Retrieve the hostname of an IP Address

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    InetAddress addr = InetAddress.getByName("127.0.0.1");
    byte[] ipAddr = new byte[] { 127, 0, 0, 1 };
    addr = InetAddress.getByAddress(ipAddr);
    // Get the host name
    String hostname = addr.getHostName();
    // Get canonical host name
    String canonicalhostname = addr.getCanonicalHostName();
  }
}

Retrieve the IP address of a hostname

   
import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    InetAddress addr = InetAddress.getByName("java-tips.org");
    byte[] ipAddr = addr.getAddress();
    // Convert to dot representation
    String ipAddrStr = "";
    for (int i = 0; i < ipAddr.length; i++) {
      if (i > 0) {
        ipAddrStr += ".";
      }
      ipAddrStr += ipAddr[i] & 0xFF;
    }
  }
}