Hello,
How to get the ip of the computer on linux through Java ?
I searched the net for examples, I found something regarding NetworkInterface class, but I can't wrap my head around how I get the Ip address.
What happens if I have multiple network interfaces running in the same time ? Which Ip address will be returned.
I would really appreciate some code samples.
P.S: I've used until now the InetAddress class which is a bad solution for cross-platform applications. (win/Linux).
What you're looking for specifically is java.net.InetAddress.getHostAddress(), here is a working example:
try {
java.net.InetAddress i = java.net.InetAddress.getLocalHost();
System.out.println(i); // name and IP address
System.out.println(i.getHostName()); // name
System.out.println(i.getHostAddress()); // IP address only
}
catch(Exception e){e.printStackTrace();}
From Java Tutorial
Why is InetAddress not a good solution? I don't see anything in the docs about cross platform compatibility?
This code will enumerate all network interfaces and retrieve their information.
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 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 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: bge0
Name: bge0
InetAddress: /fe80:0:0:0:203:baff:fef2:e99d%2
InetAddress: /121.153.225.59
Display name: lo0
Name: lo0
InetAddress: /0:0:0:0:0:0:0:1%1
InetAddress: /127.0.0.1
Java does not handle multi network systems well. You cannot control which network interface will be returned by InetAddress.getLocalHost(). The only solution I have so far to control which interface is returned by InetAddress.getLocalHost() is to use the security manager and not grant SocketPermission to the addresses that I don't want used.
InetAddress.getAllByName("localhost");
Will get you the loop back addresses.
IntetAddress ia = InetAddress.getLocalHost();
Will get you one of your IP's;
IntetAddress[] iaa = InetAddress.getAllByName(ia.getHostName());
will get you all of the addresses on your host.
The sun InetAddress implements getLocalHost() like this:
public static InetAddress getLocalHost() throws UnknownHostException {
SecurityManager security = System.getSecurityManager();
try {
String local = impl.getLocalHostName();
if (security != null) {
security.checkConnect(local, -1);
}
// we are calling getAddressFromNameService directly
// to avoid getting localHost from cache
InetAddress[] localAddrs;
try {
localAddrs =
(InetAddress[]) InetAddress.getAddressFromNameService(local);
} catch (UnknownHostException uhe) {
throw new UnknownHostException(local + ": " + uhe.getMessage());
}
return localAddrs[0];
} catch (java.lang.SecurityException e) {
return impl.loopbackAddress();
}
}
Do not forget about loopback addresses, which are not visible outside. Here is a function which extracts the first non-loopback IP(IPv4 or IPv6)
private static InetAddress getFirstNonLoopbackAddress(boolean preferIpv4, boolean preferIPv6) throws SocketException {
Enumeration en = NetworkInterface.getNetworkInterfaces();
while (en.hasMoreElements()) {
NetworkInterface i = (NetworkInterface) en.nextElement();
for (Enumeration en2 = i.getInetAddresses(); en2.hasMoreElements();) {
InetAddress addr = (InetAddress) en2.nextElement();
if (!addr.isLoopbackAddress()) {
if (addr instanceof Inet4Address) {
if (preferIPv6) {
continue;
}
return addr;
}
if (addr instanceof Inet6Address) {
if (preferIpv4) {
continue;
}
return addr;
}
}
}
}
return null;
}