package datagram;import java.io.IOException;import java.net.InetSocketAddress;import java.net.SocketAddress;import java.nio.ByteBuffer;import java.nio.channels.DatagramChannel;import java.nio.charset.Charset;public class UDPServer {    private int port = 8008;    private DatagramChannel channel;    private int MAX_SIZE = 1024;                    public UDPServer(int port, int size) throws IOException {                this.port = port;        this.MAX_SIZE = size;        channel = DatagramChannel.open();        SocketAddress localAddr = new InetSocketAddress(this.port);        channel.bind(localAddr);        System.out.println("Server Starting...");            }            public UDPServer() throws IOException {                this(8008, 1024);    }            public String echo(String msg) {                return "echo:" + msg;    }            public void service() {                ByteBuffer receiveBuffer = ByteBuffer.allocate(MAX_SIZE);        while(true) {            try {                receiveBuffer.clear();                InetSocketAddress client = (InetSocketAddress) channel.receive(receiveBuffer);                receiveBuffer.flip();                String msg = Charset.forName("GBK").decode(receiveBuffer).toString();                System.out.println(client.getAddress().getHostAddress() + ":" + client.getPort() + " > " + msg);                                channel.send(ByteBuffer.wrap(echo(msg).getBytes()), client);                                if(msg.startsWith("bye"))                    break;                            }            catch (IOException e) {                e.printStackTrace();            }        }    }            public static void main(String[] args) throws IOException {                new UDPServer().service();    }}

package datagram;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.net.InetAddress;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.CharBuffer;import java.nio.channels.DatagramChannel;import java.nio.channels.SelectionKey;import java.nio.channels.Selector;import java.nio.charset.Charset;import java.util.Iterator;import java.util.Set;public class UDPClient {    private DatagramChannel datagramChannel = null;    private ByteBuffer sendBuffer = ByteBuffer.allocate(1024);    private ByteBuffer receiveBuffer = ByteBuffer.allocate(1024);    private Charset charset = Charset.forName("GBK");    private Selector selector;            public UDPClient(int port) throws IOException {                datagramChannel = DatagramChannel.open();        InetAddress ia = InetAddress.getByName("10.11.3.220");        InetSocketAddress isa = new InetSocketAddress(ia, port);        datagramChannel.configureBlocking(false);        datagramChannel.bind(isa);                ia = InetAddress.getByName("10.11.3.160");        isa = new InetSocketAddress(ia, 8008);        datagramChannel.connect(isa);        selector = Selector.open();    }            public UDPClient() throws IOException {                this(7000);    }            public static void main(String[] args) throws IOException {                int port = 7000;        if(args.length > 0)            port = Integer.parseInt(args[0]);                final UDPClient client = new UDPClient(port);        Thread receiver = new Thread() {            public void run() {                client.receiveFromUser();            }        };                receiver.start();        client.talk();    }            public void receiveFromUser() {                try {            BufferedReader localReader = new BufferedReader(new InputStreamReader(System.in));            String msg = null;            while((msg = localReader.readLine()) != null) {                synchronized(sendBuffer) {                    sendBuffer.put(encode(msg + "\r\n"));                }                if(msg.equals("bye"))                     break;             }        }        catch (IOException e) {            e.printStackTrace();        }    }            public void talk() throws IOException {                datagramChannel.register(selector, SelectionKey.OP_READ|SelectionKey.OP_WRITE);        while(selector.select() > 0) {            Set<SelectionKey> readyKeys = selector.selectedKeys();            Iterator<SelectionKey> it = readyKeys.iterator();            while(it.hasNext()) {                SelectionKey key = null;                try {                    key = it.next();                    it.remove();                                        if(key.isReadable()) {                        receive(key);                    }                                        if(key.isWritable()) {                        send(key);                    }                }                catch (IOException e) {                    e.printStackTrace();                    try {                        if(key != null) {                            key.cancel();                            key.channel().close();                        }                    }                    catch(Exception ex) {                        ex.printStackTrace();                    }                }            }        }    }            public void send(SelectionKey key) throws IOException {                DatagramChannel datagramChannel = (DatagramChannel) key.channel();        synchronized(sendBuffer) {            sendBuffer.flip();            datagramChannel.write(sendBuffer);            sendBuffer.compact();        }    }            public void receive(SelectionKey key) throws IOException {                DatagramChannel datagramChannel = (DatagramChannel) key.channel();        datagramChannel.read(receiveBuffer);        receiveBuffer.flip();                String receiveData = decode(receiveBuffer);        if(receiveData.indexOf("\n") == -1)            return;                String outputData = receiveData.substring(0, receiveData.indexOf("\n")+1);        System.out.println(outputData);                if(outputData.equals("echo:bye\r\n")) {            key.cancel();            datagramChannel.close();            System.out.println("Closed connection with Server");            selector.close();            System.exit(0);        }                ByteBuffer temp = encode(outputData);        receiveBuffer.position(temp.limit());        receiveBuffer.compact();    }            public String decode(ByteBuffer buffer) {                CharBuffer charBuffer = charset.decode(buffer);        return charBuffer.toString();    }            public ByteBuffer encode(String str) {                return charset.encode(str);    }}