[andbin]

Ecco un esempio client-server su datagram: il client invia una stringa al server, il server riceve la stringa, la inverte e la rimanda al client.

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

public class StringReverseDatagramServer extends Thread
{
    private DatagramSocket socket;

    public StringReverseDatagramServer (int port)
        throws IOException
    {
        super ("StringReverseDatagramServer");

        socket = new DatagramSocket (port);
    }

    public void run ()
    {
        try
        {
            byte[] bufinp = new byte[256];

            DatagramPacket packet = new DatagramPacket (bufinp, bufinp.length);
            socket.receive (packet);

            String inp = new String (packet.getData (), 0, packet.getLength (), "UTF-8");
            String out = reverseString (inp);

            byte[] bufout = out.getBytes ("UTF-8");

            InetAddress address = packet.getAddress ();
            int port = packet.getPort ();
            packet = new DatagramPacket (bufout, bufout.length, address, port);
            socket.send (packet);
            socket.close ();
        }
        catch (IOException e)
        {
            e.printStackTrace ();
        }
    }

    private String reverseString (String s)
    {
        int len = s.length ();

        StringBuffer sb = new StringBuffer (len);

        for (int i=0; i<len; i++)
            sb.append (s.charAt (len-i-1));

        return sb.toString ();
    }
}

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

public class StringReverseDatagramClient
{
    public static void main (String[] args)
    {
        try
        {
            /* Avvia server */
            StringReverseDatagramServer server = new StringReverseDatagramServer (5555);
            server.start ();

            /* Avvia client */
            DatagramSocket socket = new DatagramSocket ();
            InetAddress address = InetAddress.getByName ("localhost");

            String inp = "Hello to server";

            byte[] bufinp = inp.getBytes ("UTF-8");

            DatagramPacket packet = new DatagramPacket (bufinp, bufinp.length, address, 5555);
            socket.send (packet);

            byte[] bufout = new byte[256];

            packet = new DatagramPacket (bufout, bufout.length);
            socket.receive (packet);

            String out = new String (packet.getData (), 0, packet.getLength (), "UTF-8");
            System.out.println (out);

            socket.close ();
        }
        catch (Exception e)
        {
            e.printStackTrace ();
        }
    }
}