Relaying Datagrams

Following the idea of the TCP relay, a UDP datagram relay receives datagrams on a particular port number and resends them to another address and port.

Listing 31.3 shows a simple datagram relay.

Code Listing 31.3. Source Code for DatagramRelay.java
package usingj2ee.net;

import java.net.*;
import java.io.*;

public class DatagramRelay
{
    public static void main(String[] args)
    {
        if (args.length < 3)
        {
            System.out.println("Please supply a local port, a remote host "+
                " and a remote port.");
            System.exit(0);
        }

        int localPort = 0;

        try
        {
            localPort = Integer.parseInt(args[0]);
        }
        catch (Exception exc)
        {
            System.out.println("Invalid local port: "+args[0]);
            System.exit(0);
        }  int remotePort = 0; try { remotePort = Integer.parseInt(args[2]); ...

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