public class NioServer {

    private static Map<String, SocketChannel> clientMap = new HashMap<>();

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

        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();

        serverSocketChannel.configureBlocking(false);

        ServerSocket serverSocket = serverSocketChannel.socket();

        serverSocket.bind(new InetSocketAddress(8899));

        Selector selector = Selector.open();

        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        while (true){

            try {

                selector.select();

                Set<SelectionKey> selectionKeys = selector.selectedKeys();

                selectionKeys.forEach( selectionKey -> {

                    final SocketChannel  client;

                    try{

                        //客户端向服务端发起一个连接

                        if(selectionKey.isAcceptable()){

                            ServerSocketChannel server = (ServerSocketChannel)selectionKey.channel();

                            client = server.accept();

                            client.configureBlocking(false);

                            client.register(selector, SelectionKey.OP_READ);

                            String key = "[" +  UUID.randomUUID() + "]";

                            clientMap.put(key, client);

                        }

                        //有数据可读

                        else if(selectionKey.isReadable()){

                            client = (SocketChannel)selectionKey.channel();

                            ByteBuffer readBuffer = ByteBuffer.allocate(1024);

                            int count = client.read(readBuffer);

                            if(count > 0){

                                readBuffer.flip();

                                Charset charset = Charset.forName("utf-8");

                                String receivedMessage = String.valueOf(charset.decode(readBuffer).array());

                                System.out.println(client + ": " + receivedMessage);

                                String senderKey = null;

                                for(Map.Entry<String,SocketChannel> entry : clientMap.entrySet()){

                                    if(client == entry.getValue()){

                                        senderKey = entry.getKey();

                                        break;

                                    }

                                }

                                for(Map.Entry<String,SocketChannel> entry : clientMap.entrySet()){

                                    SocketChannel value = entry.getValue();

                                    ByteBuffer writeBuffer = ByteBuffer.allocate(1024);

                                    writeBuffer.put((senderKey + ":" + receivedMessage).getBytes());

                                    writeBuffer.flip();

                                    value.write(writeBuffer);

                                }

                            }

                        }

                    }catch (Exception ex){

                        ex.printStackTrace();

                    }

                });

                selectionKeys.clear();

            }catch (Exception ex){

                ex.printStackTrace();

            }

        }

    }

}

public class NioClient {

    public static void main(String[] args) {

        try{

            SocketChannel socketChannel = SocketChannel.open();

            socketChannel.configureBlocking(false);

            Selector selector = Selector.open();

            socketChannel.register(selector, SelectionKey.OP_CONNECT);

            socketChannel.connect(new InetSocketAddress("127.0.0.1",8899));

            while (true){

                selector.select();

                Set<SelectionKey> keySet = selector.selectedKeys();

                for(SelectionKey selectionKey : keySet){

                    //与服务端已经建立好了连接

                    if(selectionKey.isConnectable()){

                        SocketChannel client = (SocketChannel)selectionKey.channel();

                        if(client.isConnectionPending()){

                            client.finishConnect();

                            //向服务端发数据

                            ByteBuffer writeBuffer = ByteBuffer.allocate(1024);

                            writeBuffer.put((LocalDateTime.now() + "连接成功").getBytes());

                            writeBuffer.flip();

                            client.write(writeBuffer);

                            //  启动一个线程，不断的读取标准输入的内容。然后将内容向回个服务端

                            ExecutorService executorService = Executors.newSingleThreadExecutor(Executors.defaultThreadFactory());

                            executorService.submit(() -> {

                                while (true){

                                    try {

                                        writeBuffer.clear();

                                        InputStreamReader input = new InputStreamReader(System.in);

                                        BufferedReader br = new BufferedReader(input);

                                        String sendMessage = br.readLine();

                                        writeBuffer.put(sendMessage.getBytes());

                                        writeBuffer.flip();

                                        client.write(writeBuffer);

                                    }catch (Exception ex){

                                        ex.printStackTrace();

                                    }

                                }

                            });

                        }

                        client.register(selector, SelectionKey.OP_READ);

                    }else if(selectionKey.isReadable()){

                        SocketChannel client = (SocketChannel)selectionKey.channel();

                        ByteBuffer readBuffer = ByteBuffer.allocate(1024);

                        int count = client.read(readBuffer);

                        if(count > 0){

                            String receivedMessage = new String(readBuffer.array(), 0, count);

                            System.out.println(receivedMessage);

                        }

                    }

                }

                keySet.clear();

            }

        }catch (Exception ex){

            ex.printStackTrace();

        }

    }

}