How to get a list of IP connected in same network (subnet) using Java

To list the hosts connected in a LAN you will need to ping all the available IP addresses on the subnet. But a ping message could be restricted by firewall thus safer way could be open a socket to each IP address in the LAN's IP address range.

Since Java 1.5 there is a ping-like method in java.net.InetAddress: public boolean isReachable(int timeout). You could use that to iterate over all the IP Addresses in your subnet... java-doc

If you mean a list of all hosts connected to the network, I think the only way that is guaranteed to work is to step through a list of IP addresses and ping them all.

That said, if you're looking for something more specific, there may be something you can look up (e.g. RMI's registry (LocateRegistry.getRegistry(host, port).list()).

Also, if you just want all the IP addresses that a given host has, have a look at NetworkInterface.getNetworkInterfaces().

this should work when the hosts on your network react to ICMP packages (ping) (>JDK 5):

public void checkHosts(String subnet){
   int timeout=1000;
   for (int i=1;i<255;i++){
       String host=subnet + "." + i;
       if (InetAddress.getByName(host).isReachable(timeout)){
           System.out.println(host + " is reachable");
       }
   }
}

invoke the method for a subnet (192.168.0.1-254) like this:

checkHosts("192.168.0");

didnt test it but should work kinda like this. Obviously this only checks the 254 hosts in the last byte of the ip address...

check:

http://download-llnw.oracle.com/javase/6/docs/api/java/net/InetAddress.html#isReachable%28int%29 http://blog.taragana.com/index.php/archive/how-to-do-icmp-ping-in-java-jdk-15-and-above/

hope that helped