Getting the Ip Address of the Current Machine Using Java

Getting the IP address of the current machine using Java

import java.net.DatagramSocket;
import java.net.InetAddress;

try(final DatagramSocket socket = new DatagramSocket()){
  socket.connect(InetAddress.getByName("8.8.8.8"), 10002);
  ip = socket.getLocalAddress().getHostAddress();
}

This way works well when there are multiple network interfaces. It always returns the preferred outbound IP. The destination 8.8.8.8 is not needed to be reachable.

Connect on a UDP socket has the following effect: it sets the destination for Send/Recv, discards all packets from other addresses, and - which is what we use - transfers the socket into "connected" state, settings its appropriate fields. This includes checking the existence of the route to the destination according to the system's routing table and setting the local endpoint accordingly. The last part seems to be undocumented officially but it looks like an integral trait of Berkeley sockets API (a side effect of UDP "connected" state) that works reliably in both Windows and Linux across versions and distributions.

So, this method will give the local address that would be used to connect to the specified remote host. There is no real connection established, hence the specified remote ip can be unreachable.

Edit:

As @macomgil says, for MacOS you can do this:

Socket socket = new Socket();
socket.connect(new InetSocketAddress("google.com", 80));
System.out.println(socket.getLocalAddress());

How to get the IP address of a machine in Java

You can get the IP address of your machine using the following call:

Inet4Address.getLocalHost().getHostAddress();

The above is in the Java APIs, so you don't need any jar for that.

Java getting my IP address

The NetworkInterface class contains all the relevant methods, but be aware that there's no such thing as "my IP". A machine can have multiple interfaces and each interface can have multiple IPs.

You can list them all with this class but which interface and IP you choose from the list depends on what you exactly need to use this IP for.

(InetAddress.getLocalHost() doesn't consult your interfaces, it simply returns constant 127.0.0.1 (for IPv4))

Java get local IP

Sounds like you have two IP addresses.

On a computer that has one network adapter, the IP address that is chosen is the Primary IP address of the network adaptor in the computer. However, on a multiple-homed computer, the stack must first make a choice. The stack cannot make an intelligent choice until it knows the target IP address for the connection.

When the program sends a connect() call to a target IP address, or sends a send() call to a UDP datagram, the stack references the target IP address, and then examines the IP route table so that it can choose the best network adapter over which to send the packet. After this network adapter has been chosen, the stack reads the Primary IP address associated with that network adapter and uses that IP address as the source IP address for the outbound packets.

Document

If you want to activate second IP and its for example LAN, unplug it and after 10 sec plug in back. Other IP might be selected as host IP in routing table.

You can get 2nd IP from getNetworkInterfaces.

Try to run followed code:

public static void main(String[] args) throws Exception
{
    System.out.println("Your Host addr: " + InetAddress.getLocalHost().getHostAddress());  // often returns "127.0.0.1"
    Enumeration<NetworkInterface> n = NetworkInterface.getNetworkInterfaces();
    for (; n.hasMoreElements();)
    {
        NetworkInterface e = n.nextElement();

        Enumeration<InetAddress> a = e.getInetAddresses();
        for (; a.hasMoreElements();)
        {
            InetAddress addr = a.nextElement();
            System.out.println("  " + addr.getHostAddress());
        }
    }
} 

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