Basic Sockets - TCP/IP Sockets in Java Practical Guide for Programmers - page 27

1. Send the echo string to the server.

2. Block on receive() for up to three seconds, starting over (up to five times) if the reply is
not received before the timeout.

3. Terminate the client.

UDPEchoClientTimeout.java

0 import java.net.*; // for DatagramSocket, DatagramPacket, and InetAddress
1 import java.io.*; // for IOException

2
3 public class UDPEchoClientTimeout {
4
5 private static final int TIMEOUT = 3000; // Resend timeout (milliseconds)

6 private static final int MAXTRIES = 5; // Maximum retransmissions

7
8

public static void main(String[] args) throws IOException {

9
10

if ((args.length < 2) || (args.length > 3)) // Test for correct # of args

11

throw new IllegalArgumentException("Parameter(s): <Server> <Word> [<Port>]");

12
13

InetAddress serverAddress = InetAddress.getByName(args[0]); // Server address

14

// Convert the argument String to bytes using the default encoding

15

byte[] bytesToSend = args[1].getBytes();

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int servPort = (args.length == 3) ? Integer.parseInt(args[2]) : 7;

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DatagramSocket socket = new DatagramSocket();

20
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socket.setSoTimeout(TIMEOUT); // Maximum receive blocking time (milliseconds)

22
23 DatagramPacket sendPacket = new DatagramPacket(bytesToSend, // Sending packet

24 bytesToSend.length, serverAddress, servPort);

25
26

DatagramPacket receivePacket = // Receiving packet

27 new DatagramPacket(new byte[bytesToSend.length], bytesToSend.length);

28
29 int tries = 0; // Packets may be lost, so we have to keep trying

30 boolean receivedResponse = false;

31

do {

32

socket.send(sendPacket); // Send the echo string

33

try {

34

socket.receive(receivePacket); // Attempt echo reply reception

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if (!receivePacket.getAddress().equals(serverAddress)) // Check source

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throw new IOException("Received packet from an unknown source");

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receivedResponse = true;