Java - 关闭UDP套接字

Question

I am trying to simulate UDP using Java. I am sending a file from one host to another. This is the part of the receiver:

server.setSoTimeout(10000);     
while (true)
{
    try 
    {
        DatagramPacket received = new DatagramPacket(receivedData,receivedData.length);
        server.receive(received);
        out.write(received.getData());
    } 
    catch (IOException e) {
                break;
            }



    }
server.close();

This solution works, but I am not satisfied with it for some reason.

Sender sends all the packets and then it closes the DatagramSocket. Receiver gets all the packets and it terminates, but it terminates because of the timeout.

So if switch on my receiver and don't execute anything for 10 secs, my Receiver shuts off, so nothing is transmitted.

Is there a way of terminating the loop without specifying the timeout?

I was also wondering if there is a method for the other host to establish connection - something like ServerSocket.accept(), which basically waits for the other host to connect.But, I decided to use DatagramSocket and I can't find a solution to this issue.

Does anybody know of a method that would perform this?

Answer 1

No.

Datagram (UDP) sockets are inherently connectionless. Closing a DatagramSocket does not have any effect which is visible to a remote system. It prevents an application from sending or receiving any further data on that socket, and frees up the port for use by other applications on the local system, but it does not cause any notification to be sent over the network.

If you want to notify the remote server that you are done sending data, you will need to send them a datagram notifying them of that.

If you are trying to transfer a file over UDP, keep in mind that UDP packets are not guaranteed to be received, nor are they guaranteed to be received in the same order they are transmitted! (That is, they may be dropped or reordered by the network.)