This example program extracts the IP address of the client and print to the console.

Java Code:
import java.net.*;
import java.io.*;
import java.applet.*;

public class GetClientIP extends Applet {
  public void init() {
    try {
     InetAddress thisIp =
        InetAddress.getLocalHost();
     System.out.println("IP:"+thisIp.getHostAddress());
     }
    catch(Exception e) {
     e.printStackTrace();
     }
    }
}