The java.net.DatagramSocket class has three constructors:
public DatagramSocket() throws SocketException
public DatagramSocket(int port) throws
SocketException
public DatagramSocket(int port, InetAddress
laddr) throws SocketException
The first is used for datagram
sockets that are primarily intended to act as clients; that is sockets that
will send datagrams before receiving any.
The secned two that specify the port
and optionally the IP address of the socket, are primarily intended for servers
that must run on a well-known port.
The LocalPortScanner developed
earlier only found TCP ports. The following program detects UDP ports in use.
import java.net.*;
import java.io.IOException;
public class NetparamScanner {
public static void main(String[] args) {
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 ex) {
}
}
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 ex) {
System.out.println("UDP Port
" + port + " is occupied.");
}
}
}
}
Since UDP is connectionless it is
not possible to write a remote UDP port scanner. The only way you know whether
or not a UDP server is listening on a remote port is if it sends something back
to you.
