Getting the external IP address in Java

Question

I m not too sure how to go about getting the external IP address of the machine as a computer outside of a network would see it   My following IPAddress class only gets the local IP address of the machine   public class IPAddress        private InetAddress thisIp       private String thisIpAddress       private void setIpAdd             try               InetAddress thisIp   InetAddress getLocalHost                thisIpAddress   thisIp getHostAddress   toString              catch  Exception e                         protected String getIpAddress             setIpAdd            return thisIpAddress

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System out println pageCrawling getHtmlFromURL  http   ipecho net plain

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It s not that easy since a machine inside a LAN usually doesn t care about the external IP of its router to the internet   it simply doesn t need it   I would suggest you to exploit this by opening a site like http   www whatismyip com  and getting the IP number by parsing the html results   it shouldn t be that hard

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How about this  It s simple and worked the best for me     import java io BufferedReader  import java io IOException  import java io InputStreamReader  import java net MalformedURLException  import java net URL    public class IP       public static void main String args              new IP               public IP             URL ipAdress           try               ipAdress   new URL  http   myexternalip com raw                 BufferedReader in   new BufferedReader new InputStreamReader ipAdress openStream                   String ip   in readLine                System out println ip             catch  MalformedURLException e                e printStackTrace              catch  IOException e                e printStackTrace

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I am not sure if you can grab that IP from code that runs on the local machine   You can however build code that runs on a website  say in JSP  and then use something that returns the IP of where the request came from   request getRemoteAddr    Or simply use already-existing services that do this  then parse the answer from the service to find out the IP   Use a webservice like AWS and others  import java net    import java io     URL whatismyip   new URL  http   checkip amazonaws com    BufferedReader in   new BufferedReader new InputStreamReader                  whatismyip openStream       String ip   in readLine      you get the IP as a String System out println ip

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An alternative solution is to execute an external command  obviously  this solution limits the portability of the application    For example  for an application that runs on Windows  a PowerShell command can be executed through jPowershell  as shown in the following code   public String getMyPublicIp            PowerShell command     String command    quot  Invoke-WebRequest ifconfig me ip  Content Trim   quot       String powerShellOut   PowerShell executeSingleCommand command  getCommandOutput            Connection failed     if  powerShellOut contains  quot InvalidOperation quot              powerShellOut   null            return powerShellOut

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As  Donal Fellows wrote  you have to query the network interface instead of the machine  This code from the javadocs worked for me   The following example program lists all the network interfaces and their addresses on a machine   import java io    import java net    import java util    import static java lang System out   public class ListNets        public static void main String args    throws SocketException           Enumeration lt NetworkInterface gt  nets   NetworkInterface getNetworkInterfaces            for  NetworkInterface netint   Collections list nets               displayInterfaceInformation netint              static void displayInterfaceInformation NetworkInterface netint  throws SocketException           out printf  Display name   s n   netint getDisplayName             out printf  Name   s n   netint getName             Enumeration lt InetAddress gt  inetAddresses   netint getInetAddresses            for  InetAddress inetAddress   Collections list inetAddresses                 out printf  InetAddress   s n   inetAddress                     out printf   n                The following is sample output from the example program   Display name  TCP Loopback interface Name  lo InetAddress   127 0 0 1  Display name  Wireless Network Connection Name  eth0 InetAddress   192 0 2 0   From docs oracle com

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Make a HttpURLConnection to some site like www whatismyip com and parse that  -

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One of the comments by  stivlo deserves to be an answer   You can use the Amazon service http   checkip amazonaws com  import java io BufferedReader  import java io IOException  import java io InputStreamReader  import java net URL   public class IpChecker        public static String getIp   throws Exception           URL whatismyip   new URL  http   checkip amazonaws com            BufferedReader in   null          try               in   new BufferedReader new InputStreamReader                      whatismyip openStream                  String ip   in readLine                return ip            finally               if  in    null                    try                       in close                      catch  IOException e                        e printStackTrace

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If you are using JAVA based webapp and if you want to grab the client s  One who makes the request via a browser  external ip try deploying the app in a public domain and use request getRemoteAddr   to read the external IP address

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http   jstun javawi de  will do it - provided your gateway device does STUN  most do

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The truth is   you can t  in the sense that you posed the question  NAT happens outside of the protocol  There is no way for your machine s kernel to know how your NAT box is mapping from external to internal IP addresses  Other answers here offer tricks involving methods of talking to outside web sites

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All this are still up and working smoothly   as of 23 Sep 2019    http   checkip amazonaws com  https   ipv4 icanhazip com   works with ipv6 as subdomain too   http   myexternalip com raw http   ipecho net plain http   bot whatismyipaddress com http   www trackip net ip  only gives ipv6  http   curlmyip com   17 Dec 2016    Piece of advice  Do not direcly depend only on one of them  try to use one but have a contigency plan considering others  The more you use  the better   Good luck

[java] Getting the 'external' IP address in Java

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