Java UDP socket non-blocking?

Question

I have a UDP socket and I am waiting for requests from clients. Upon request I read a line from a file and send a datagram back with that line as payload. But the socket.receive() seems only to be blocking for the first request (loop-iteration), subsequent socket.receive() calls don't block anymore. Is that normal? Why could this be?

String input;
DatagramSocket socket = new DatagramSocket(port);
DatagramPacket answer;
while((input=fileIn.readline()))!=null){
  socket.receive(request);
  ...
  //send answer back
  byte[] load = input.getBytes();
  answer = new DatagramPacket(load, load.length, address, port);
  socket.send(answer);
 }
 socket.close();

The programm already sends all the filedata , so all lines of the file after the 1st request., and therefore jumps over the blocking socket.receive().