Java Tutorial/Network/UDP Server

UDP Echo Server With Channels

import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
public class MainClass {
  public static void main(String[] args) throws Exception {
    DatagramChannel channel = DatagramChannel.open();
    DatagramSocket socket = channel.socket();
    SocketAddress address = new InetSocketAddress(9999);
    socket.bind(address);
    ByteBuffer buffer = ByteBuffer.allocateDirect(65507);
    while (true) {
      SocketAddress client = channel.receive(buffer);
      buffer.flip();
      channel.send(buffer, client);
      buffer.clear();
    }
  }
}

UDP pocket sender and receiver

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
class PacketReceiver {
  public static void main(String[] args) throws Exception {
    byte[] buffer = new byte[1024];
    DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
    DatagramSocket socket = new DatagramSocket(5002);
    socket.receive(packet);
    System.out.println(packet.getSocketAddress());
    buffer = packet.getData();
    System.out.println(new String(buffer));
  }
}
class PacketSender {
  public static void main(String[] args) throws Exception {
    byte[] buffer = "data".getBytes();
    DatagramPacket packet = new DatagramPacket(buffer, buffer.length, new InetSocketAddress(
        "localhost", 5002));
    DatagramSocket socket = new DatagramSocket(5003);
    socket.send(packet);
  }
}

UDP time server based on New IO

import java.io.IOException;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.DatagramChannel;
public class UDPTimeServer {
  public final static int DEFAULT_PORT = 37;
  public static void main(String[] args) throws IOException {
    int port = 37;
    ByteBuffer in = ByteBuffer.allocate(8192);
    ByteBuffer out = ByteBuffer.allocate(8);
    out.order(ByteOrder.BIG_ENDIAN);
    SocketAddress address = new InetSocketAddress(port);
    DatagramChannel channel = DatagramChannel.open();
    DatagramSocket socket = channel.socket();
    socket.bind(address);
    System.err.println("bound to " + address);
    while (true) {
      try {
        in.clear();
        SocketAddress client = channel.receive(in);
        System.err.println(client);
        long secondsSince1970 = System.currentTimeMillis();
        out.clear();
        out.putLong(secondsSince1970);
        out.flip();
        out.position(4);
        channel.send(out, client);
      } catch (Exception ex) {
        System.err.println(ex);
      }
    }
  }
}