Java Tutorial/Network/Internet Addresses

Compare two InetAddresses

import java.net.InetAddress;
public class MainClass {
  public static void main(String args[]) throws Exception {
    InetAddress ca = InetAddress.getByName("www.google.ca");
    InetAddress com = InetAddress.getByName("www.google.ru");
    if (ca.equals(com)) {
      System.out.println("same");
    } else {
      System.out.println("not the same");
    }
  }
}

not the same

Create InetAddress by Name

import java.net.InetAddress;
public class MainClass {
  public static void main(String[] args) {
    try {
      InetAddress ia = InetAddress.getByName("64.21.29.37");
      System.out.println(ia.getHostName());
    } catch (Exception ex) {
      System.err.println(ex);
    }
  }
}

Get All addresses by name

import java.net.*;
public class MainClass {
  public static void main (String[] args) {
    try {
      InetAddress[] addresses = InetAddress.getAllByName("www.google.ru");
      for (int i = 0; i < addresses.length; i++) {
        System.out.println(addresses[i]);
      }
    }
    catch (UnknownHostException e) {
      System.out.println("Could not find www.apple.ru");
    }
  }
}

www.google.ru/72.14.253.147
www.google.ru/72.14.253.99
www.google.ru/72.14.253.103
www.google.ru/72.14.253.104

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 Host name from InetAddress

import java.net.InetAddress;
import java.net.UnknownHostException;
public class MainClass {
  public static void main(String[] args) {
    try {
      InetAddress address = InetAddress.getLocalHost();
      System.out.println("My name is " + address.getHostName());
    } catch (UnknownHostException e) {
      System.out.println("I"m sorry. I don"t know my own name.");
    }
  }
}

Get local host from InetAddress

import java.net.InetAddress;
import java.net.UnknownHostException;
public class MainClass {
  public static void main(String[] args) {
    try {
      InetAddress me = InetAddress.getLocalHost();
      String dottedQuad = me.getHostAddress();
      System.out.println("My address is " + dottedQuad);
    } catch (UnknownHostException e) {
      System.out.println("I"m sorry. I don"t know my own address.");
    }
  }
}

Get my own address

import java.net.InetAddress;
public class MainClass {
  public static void main(String[] args) {
    try {
      InetAddress me = InetAddress.getLocalHost();
      String dottedQuad = me.getHostAddress();
      System.out.println("My address is " + dottedQuad);
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }
}

Getting 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("www.google.ru");
    System.out.println(addr.getHostAddress());
    
  }
}

java.net.InetAddress.isReachable(int) can be used to check if a server is reachable or not.

import java.net.InetAddress;
public class Main {
  public static void main(String[] argv) throws Exception {
    InetAddress address = InetAddress.getByName("web.mit.edu");
    System.out.println("Name: " + address.getHostName());
    System.out.println("Addr: " + address.getHostAddress());
    System.out.println("Reach: " + address.isReachable(3000));
  }
}

Ping a host

import java.net.InetAddress;
public class Main {
  public static void main(String[] args) throws Exception {
    InetAddress address = InetAddress.getByName("17.16.15.14");
    boolean reachable = address.isReachable(10000);
    System.out.println("Is host reachable? " + reachable);
  }
}

Translate host names to Internet addresses

import java.net.InetAddress;
import java.net.UnknownHostException;
public class MainClass {
  public static void main(String args[]) {
    try {
      InetAddress inetAddr = InetAddress.getByName("www.jexp.ru");
      System.out.println(inetAddr.toString());
    } catch (UnknownHostException ex) {
    }
  }
}

www.jexp.ru/208.109.14.69