Connect to a daytime server using the UDP protocol
/*
* Copyright (c) 2004 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 3nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose,
* including teaching and use in open-source projects.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book,
* please visit http://www.davidflanagan.com/javaexamples3.
*/
//package je3.nio;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketTimeoutException;
/**
* Connect to a daytime server using the UDP protocol. We use java.net instead
* of java.nio because DatagramChannel doesn't honor the setSoTimeout() method
* on the underlying DatagramSocket
*/
public class DaytimeClient {
public static void main(String args[]) throws java.io.IOException {
// Figure out the host and port we're going to talk to
String host = args[0];
int port = 13;
if (args.length > 1)
port = Integer.parseInt(args[1]);
// Create a socket to use
DatagramSocket socket = new DatagramSocket();
// Specify a 1-second timeout so that receive() does not block forever.
socket.setSoTimeout(1000);
// This buffer will hold the response. On overflow, extra bytes are
// discarded: there is no possibility of a buffer overflow attack here.
byte[] buffer = new byte[512];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length, new InetSocketAddress(host,
port));
// Try three times before giving up
for (int i = 0; i < 3; i++) {
try {
// Send an empty datagram to the specified host (and port)
packet.setLength(0); // make the packet empty
socket.send(packet); // send it out
// Wait for a response (or timeout after 1 second)
packet.setLength(buffer.length); // make room for the response
socket.receive(packet); // wait for the response
// Decode and print the response
System.out.print(new String(buffer, 0, packet.getLength(), "US-ASCII"));
// We were successful so break out of the retry loop
break;
} catch (SocketTimeoutException e) {
// If the receive call timed out, print error and retry
System.out.println("No response");
}
}
// We're done with the channel now
socket.close();
}
}
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