场景很简单，就是多个客户端通过udp，连接到服务器(其实是无连接的，就是服务器保存了客户端的ip信息)。然后通过udp协议先服务器发送消息，然后服务器在通过udp转发在各个客服端。

这个是不是 观察者模式

server代码

public class Server {

private static LinkedList list=new LinkedList();

private static final ExecutorService executorService = Executors.newFixedThreadPool(4);//这里用多线程去转发，可以提高效率。emmm，udp没有3次握手，速度应该很快，多不多线程应该差不了太多

private static DatagramChannel server=null;

private static Selector selector=null;

static {

try{

server=DatagramChannel.open().bind(new InetSocketAddress(8889));

server.configureBlocking(false);

selector=Selector.open();

}catch (Exception e){

e.printStackTrace();

}

}

public static void main(String[] args)throws Exception {

server.register(selector, SelectionKey.OP_READ);

while (true){

if (selector.select()>0){

Set keys = selector.selectedKeys();

Iterator iterator = keys.iterator();

while (iterator.hasNext()){

SelectionKey selectionKey = iterator.next();

if (selectionKey.isReadable()){

String msg = readMsg(selectionKey);

broadcast(msg);

}

iterator.remove();

}}

}

}

public static void saveIP(SocketAddress address)throws Exception{

if (!list.contains(address)){

list.add(address);

System.out.println("新增ip："+address);

}

System.out.println("当前udp 保存的ip数量："+list.size());

}

public static void broadcast(String msg) throws Exception{

//DatagramPacket packet=new DatagramPacket(msg.getBytes(),0,msg.getBytes().length);

for (SocketAddress address:list

) {

ByteBuffer byteBuffer=ByteBuffer.wrap(msg.getBytes());

executorService.submit(new Runnable() {

@Override

public void run() {

try{

server.send(byteBuffer, address);

System.out.println(Thread.currentThread().getName()+":"+address+"发送成功");

}catch (Exception e){

System.out.println(Thread.currentThread().getName()+":"+address+"发送失败");

}

}

});

}

}

public static String readMsg(SelectionKey selectionKey)throws Exception{

DatagramChannel channel=(DatagramChannel)selectionKey.channel();

System.out.println(channel.getRemoteAddress()+":"+channel.getLocalAddress());

ByteBuffer byteBuffer=ByteBuffer.allocate(1024);

SocketAddress receive = channel.receive(byteBuffer);

saveIP(receive);

byteBuffer.flip();

String msg=new String(byteBuffer.array(),"utf-8");

System.out.println("收到消息："+msg);

return msg;

}

}

client 代码

public class Client {

public static DatagramSocket socket=null;

public static void main(String[] args) throws Exception{

try {

socket=new DatagramSocket();

Scanner scanner=new Scanner(System.in);

String msg;

new Thread(()->{

try{

while (true){

byte[] arr=new byte[1024];

DatagramPacket packet=new DatagramPacket(arr,arr.length);

socket.receive(packet);

String m1=new String(packet.getData(),"utf-8");

System.out.println("受到服务器消息:"+m1);

}

}catch (Exception e){

e.printStackTrace();

}

}).start();

while (!(msg=scanner.nextLine()).equals("exit")){

DatagramPacket packet=new DatagramPacket(msg.getBytes(),msg.getBytes().length,new InetSocketAddress("127.0.0.1",8889));

socket.send(packet);

}

}finally {

socket.close();

}

}

}