server side:

import java.io.*;
import java.net.*;
class ftp
{
public static void main(String args[])throws IOException,SocketException
{
DataInputStream dis = new DataInputStream(System.in);
File file = new File("yourfile");
FileInputStream fis = new FileInputStream(file);
byte[] b = new byte[(int)file.length()];
fis.read(b,0,b.length);
DatagramSocket ds = new DatagramSocket(1000);
DatagramPacket dp = new DatagramPacket(b,b.length,InetAddress.getLocalHost(),2000);
ds.send(dp);
}
}

Client side:

import java.io.*;
import java.net.*;
class ftpclient
{
public static void main(String args[])throws IOException,SocketException
{
byte[] b = new byte[3000];
DatagramSocket ds = new DatagramSocket(2000);
DatagramPacket dp = new DatagramPacket(b,b.length);
FileOutputStream fos = new FileOutputStream(new File("copy-yourfile"));
ds.receive(dp);
byte[] b1 = new byte[dp.getLength()];
fos.write(b,0,b1.length);
}
}