How to enumerate IP addresses of all enabled NIC cards from Java?

This is pretty easy:

try {  InetAddress localhost = InetAddress.getLocalHost();  LOG.info(" IP Addr: " + localhost.getHostAddress());  // Just in case this host has multiple IP addresses....  InetAddress[] allMyIps = InetAddress.getAllByName(localhost.getCanonicalHostName());  if (allMyIps != null && allMyIps.length > 1) {    LOG.info(" Full list of IP addresses:");    for (int i = 0; i < allMyIps.length; i++) {      LOG.info("    " + allMyIps[i]);    }  }} catch (UnknownHostException e) {  LOG.info(" (error retrieving server host name)");}try {  LOG.info("Full list of Network Interfaces:");  for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();) {    NetworkInterface intf = en.nextElement();    LOG.info("    " + intf.getName() + " " + intf.getDisplayName());    for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements(); ) {      LOG.info("        " + enumIpAddr.nextElement().toString());    }  }} catch (SocketException e) {  LOG.info(" (error retrieving network interface list)");}

Some of this will only work in JDK 1.6 and above (one of the methods was added in that release.)

List<InetAddress> addrList = new ArrayList<InetAddress>();for(Enumeration<NetworkInterface> eni = NetworkInterface.getNetworkInterfaces(); eni.hasMoreElements(); ) {   final NetworkInterface ifc = eni.nextElement();   if(ifc.isUp()) {      for(Enumeration<InetAddress> ena = ifc.getInetAddresses(); ena.hasMoreElements(); ) {        addrList.add(ena.nextElement());      }   }}

Prior to 1.6, it's a bit more difficult - isUp() isn't supported until then.

FWIW: The Javadocs note that this is the correct approach for getting all of the IP addresses for a node:

NOTE: can use getNetworkInterfaces()+getInetAddresses() to obtain all IP addresses for this node

This code only works in Java 1.6 because of the added InterfaceAddress code.

  try  {     System.out.println("Output of Network Interrogation:");     System.out.println("********************************\n");     InetAddress theLocalhost = InetAddress.getLocalHost();     System.out.println(" LOCALHOST INFO");     if(theLocalhost != null)     {        System.out.println("          host: " + theLocalhost.getHostName());        System.out.println("         class: " + theLocalhost.getClass().getSimpleName());        System.out.println("            ip: " + theLocalhost.getHostAddress());        System.out.println("         chost: " + theLocalhost.getCanonicalHostName());        System.out.println("      byteaddr: " + toMACAddrString(theLocalhost.getAddress()));        System.out.println("    sitelocal?: " + theLocalhost.isSiteLocalAddress());        System.out.println("");     }     else     {        System.out.println(" localhost was null");     }     Enumeration<NetworkInterface> theIntfList = NetworkInterface.getNetworkInterfaces();     List<InterfaceAddress> theAddrList = null;     NetworkInterface theIntf = null;     InetAddress theAddr = null;     while(theIntfList.hasMoreElements())     {        theIntf = theIntfList.nextElement();        System.out.println("--------------------");        System.out.println(" " + theIntf.getDisplayName());        System.out.println("          name: " + theIntf.getName());        System.out.println("           mac: " + toMACAddrString(theIntf.getHardwareAddress()));        System.out.println("           mtu: " + theIntf.getMTU());        System.out.println("        mcast?: " + theIntf.supportsMulticast());        System.out.println("     loopback?: " + theIntf.isLoopback());        System.out.println("          ptp?: " + theIntf.isPointToPoint());        System.out.println("      virtual?: " + theIntf.isVirtual());        System.out.println("           up?: " + theIntf.isUp());        theAddrList = theIntf.getInterfaceAddresses();        System.out.println("     int addrs: " + theAddrList.size() + " total.");        int addrindex = 0;        for(InterfaceAddress intAddr : theAddrList)        {           addrindex++;           theAddr = intAddr.getAddress();           System.out.println("            " + addrindex + ").");           System.out.println("            host: " + theAddr.getHostName());           System.out.println("           class: " + theAddr.getClass().getSimpleName());           System.out.println("              ip: " + theAddr.getHostAddress() + "/" + intAddr.getNetworkPrefixLength());           System.out.println("           bcast: " + intAddr.getBroadcast().getHostAddress());           int maskInt = Integer.MIN_VALUE >> (intAddr.getNetworkPrefixLength()-1);           System.out.println("            mask: " + toIPAddrString(maskInt));           System.out.println("           chost: " + theAddr.getCanonicalHostName());           System.out.println("        byteaddr: " + toMACAddrString(theAddr.getAddress()));           System.out.println("      sitelocal?: " + theAddr.isSiteLocalAddress());           System.out.println("");        }     }  }  catch (SocketException e)  {     e.printStackTrace();  }  catch (UnknownHostException e)  {     e.printStackTrace();  }

The "toMACAddrString" method looks like this:

public static String toMACAddrString(byte[] a){  if (a == null)  {     return "null";  }  int iMax = a.length - 1;  if (iMax == -1)  {     return "[]";  }  StringBuilder b = new StringBuilder();  b.append('[');  for (int i = 0;; i++)  {     b.append(String.format("%1$02x", a[i]));     if (i == iMax)     {        return b.append(']').toString();     }     b.append(":");  }}

and the "toIPAddrString" method is here:

public static String toIPAddrString(int ipa){   StringBuilder b = new StringBuilder();   b.append(Integer.toString(0x000000ff & (ipa >> 24)));   b.append(".");   b.append(Integer.toString(0x000000ff & (ipa >> 16)));   b.append(".");   b.append(Integer.toString(0x000000ff & (ipa >> 8)));   b.append(".");   b.append(Integer.toString(0x000000ff & (ipa)));   return b.toString();}

I have that first set of code in the try/catch above in a method called dump() in class called IPConfig. Then I just put a main method in IPConfig to call new IPConfig().dump() so that when I'm trying to figure out some wacky network problem, I can see Java thinks is going on. I figured out that my Fedora box reports different information than Windows for the LocalHost information and it was causing my Java programs some issues.

I realize its similiar to the other answers but it prints out nearly everything interesting that you can get from the interface and ipaddress apis.