DaytimeClient.java Source code

Introduction

Here is the source code for DaytimeClient.java

Source

/*
 * 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();
    }
}