java.net.DatagramSocket

 public DatagramSocket() throws SocketException
 public DatagramSocket(int port) throws SocketException
 public DatagramSocket(int port, InetAddress laddr) throws SocketException

The LocalPortScanner developed earlier only found TCP ports. The following program detects UDP ports in use. As with TCP ports, you must be root on Unix systems to bind to ports below 1024.

import java.net.*;
import java.io.IOException;


public class UDPPortScanner {

  public static void main(String[] args) {

    // first test to see whether or not we can bind to ports
    // below 1024
    boolean rootaccess = false;
    for (int port = 1; port < 1024; port += 50) {
      try {
        ServerSocket ss = new ServerSocket(port);
        // if successful
        rootaccess = true;
        ss.close();
        break;
      }
      catch (IOException e) {
      }
    }
    
    int startport = 1;
    if (!rootaccess) startport = 1024;
    int stopport = 65535;
    
    for (int port = startport; port <= stopport; port++) {
      try {
        DatagramSocket ds = new DatagramSocket(port);
        ds.close();
      }
      catch (IOException e) {
        System.out.println("UDP Port " + port + " is occupied.");
      }
    
    }

  }

}