UDP Echo implementation using Java

In the following program, we will demonstrate, how data can be transferred between client and server using Transport Layer Protocol - UDP. This code is self-explanatory. Hence, first, you will learn to develop a server-side application. Then, you will learn to develop client-side applications.

We know that UDP is a connectionless protocol, hence at the time of testing you may not get a response from the server in many times.

EchoServer.java

import java.net.*; import java.io.*; public class EchoServer { public static final int SERVICE_PORT = 7; public static final int BUFSIZE = 4096; private DatagramSocket socket; public EchoServer() { try { socket = new DatagramSocket( SERVICE_PORT ); System.out.println ("Server active on port " + socket.getLocalPort() ); } catch (Exception e) { System.err.println ("Unable to bind port"); } } public void serviceClients() { byte[] buffer = new byte[BUFSIZE]; for (;;) { try { DatagramPacket packet = new DatagramPacket( buffer, BUFSIZE ); socket.receive(packet); System.out.println ("Packet received from " + packet.getAddress() + ":" + packet.getPort() +" of length " + packet.getLength() ); socket.send(packet); } catch (IOException ioe) { System.err.println ("Error : " + ioe); } } } public static void main(String args[]) { EchoServer server = new EchoServer(); server.serviceClients(); } }

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EchoClient.java

import java.io.BufferedReader; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStreamReader; import java.io.InterruptedIOException; import java.net.DatagramPacket; import java.net.DatagramSocket; import java.net.InetAddress; import java.net.UnknownHostException; public class EchoClient { public static final int SERVICE_PORT = 7; public static final int BUFSIZE = 256; public static void main(String args[]) { if (args.length != 1) { System.err.println("Syntax - java EchoClient hostname"); return; } String hostname = args[0]; InetAddress addr = null; try { addr = InetAddress.getByName(hostname); } catch (UnknownHostException uhe) { System.err.println("Unable to resolve host"); return; } try { DatagramSocket socket = new DatagramSocket(); socket.setSoTimeout(2 * 1000); for (int i = 1; i <= 10; i++) { String message = "Packet number " + i; char[] cArray = message.toCharArray(); byte[] sendbuf = new byte[cArray.length]; for (int offset = 0; offset < cArray.length; offset++) { sendbuf[offset] = (byte) cArray[offset]; } DatagramPacket sendPacket = new DatagramPacket(sendbuf, cArray.length, addr, SERVICE_PORT); System.out.println("Sending packet to " + hostname); socket.send(sendPacket); System.out.print("Waiting for packet.... "); byte[] recbuf = new byte[BUFSIZE]; DatagramPacket receivePacket = new DatagramPacket(recbuf, BUFSIZE); boolean timeout = false; try { socket.receive(receivePacket); } catch (InterruptedIOException ioe) { timeout = true; } if (!timeout) { System.out.println("packet received!"); System.out.println("Details : " + receivePacket.getAddress()); ByteArrayInputStream bin = new ByteArrayInputStream(receivePacket.getData(), 0, receivePacket.getLength()); BufferedReader reader = new BufferedReader(new InputStreamReader(bin)); for (;;) { String line = reader.readLine(); if (line == null) break; else System.out.println(line); } } else { System.out.println("packet lost!"); } try { Thread.sleep(1000); } catch (InterruptedException ie) { } } } catch (IOException ioe) { System.err.println("Socket error " + ioe); } } }

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Happy Exploring!