public class NioServer {
    private static ByteBuffer readBuffer;
    private static Selector selector;
    public static void main(String[] args)  throws Exception{
          // 服務(wù)端的初始化
          init();
          listen();
    }
    private static void init(){
        // 讀取請求數(shù)據(jù)的 Buffer
        readBuffer = ByteBuffer.allocate(128);
        ServerSocketChannel serverSocketChannel;
        try{
            // 1.打開服務(wù)端
            serverSocketChannel = ServerSocketChannel.open();
            // 配置為非阻塞IO
            serverSocketChannel.configureBlocking(false);
            // 設(shè)置端口，
            serverSocketChannel.socket().bind(new InetSocketAddress(9000),100);
            // 打開 多路復(fù)用選擇器
            selector = Selector.open();
            // 2.把 serverSocketChannel 注冊到 selector 上。 監(jiān)聽 serverSocketChannel 的連接請求事件，與各個(gè)客戶端建立連接請求
            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        }catch (IOException e){
            e.printStackTrace();
        }
    }
    private static void listen(){
        while (true){
            try{
                // 3. selector查看是否有注冊在 selector 上的 Channel 有網(wǎng)絡(luò)事件發(fā)生。這個(gè)方法是阻塞的。
                selector.select();
                Iterator<SelectionKey> keysIterator = selector.selectedKeys().iterator();
                // 4. 輪詢 SelectionKey 集合里的 SelectionKey，一個(gè) SelectionKey 代表一個(gè)網(wǎng)絡(luò)事件。
                while (keysIterator.hasNext()){
                    SelectionKey key = (SelectionKey) keysIterator.next();
                    keysIterator.remove();
                    handleKey(key);
                }
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }
    private static void handleKey(SelectionKey key){
        SocketChannel channel = null;
        // 5. 判斷網(wǎng)絡(luò)事件的類型并做出相應(yīng)的處理
        try {
            // 如果是客戶端要求連接的請求
            if(key.isAcceptable()){
                ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
                // 通過 TCP 三次握手，建立和獲取獲取客戶端和服務(wù)器的連接SocketChannel
                channel = serverSocketChannel.accept();
                channel.configureBlocking(false);
                // 注冊網(wǎng)絡(luò)讀事件
                channel.register(selector,SelectionKey.OP_READ);
                //如果是可以網(wǎng)絡(luò)讀的事件
            }else if(key.isReadable()){
                channel = (SocketChannel) key.channel();
                readBuffer.clear();// postion 變?yōu)?，limit = capacity,也就是復(fù)位操作，準(zhǔn)備把數(shù)據(jù)寫入Buffer了
                int count = channel.read(readBuffer); // 通過 Socket 來讀取數(shù)據(jù)并把數(shù)據(jù)寫入 Buffer 中。
                if(count > 0){
                    readBuffer.flip();// 開始從Buffer讀數(shù)據(jù)。
                    String request = StandardCharsets.UTF_8.decode(readBuffer).toString();
                    System.out.println("Server receive the request: "+request);
                    String response = "Server accept request";
                    channel.write(ByteBuffer.wrap(response.getBytes()));
                }
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

public class NioClient {
    public static void main(String[] args) throws Exception{
        // 啟動十個(gè)線程，模擬十個(gè)客戶端。
        for(int i=0;i<10;i++){
            new Worker().start();
        }
    }
    static class Worker extends Thread{
        @Override
        public void run() {
            SocketChannel channel = null;
            Selector selector = null;
            try{
                // 1.創(chuàng)建一個(gè) SocketChannel,用來與服務(wù)端連接，并實(shí)現(xiàn)網(wǎng)絡(luò)讀寫操作。
                channel = SocketChannel.open();
                channel.configureBlocking(false);
                // 指定網(wǎng)絡(luò)地址，通過三次握手實(shí)現(xiàn) TCP 連接
                channel.connect(new InetSocketAddress("localhost",9000));
                // 創(chuàng)建一個(gè) selector 對象， 并把 SocketChannel 注冊到 selector 上，并監(jiān)聽 請求連接事件 OP_CONNECT
                selector = Selector.open();
                channel.register(selector, SelectionKey.OP_CONNECT);
                // 2. 遍歷網(wǎng)絡(luò)事件
                while (true){
                    // 查找收到的網(wǎng)絡(luò)事件
                    selector.select();
                    Iterator<SelectionKey> keyIterator = selector.selectedKeys().iterator();
                    while (keyIterator.hasNext()){
                        SelectionKey key = (SelectionKey) keyIterator.next();
                        keyIterator.remove();
                        // 3. 判斷是否可以連接
                        if(key.isConnectable()){
                            // 如果連接成功了
                            if(channel.finishConnect()){
                                // 監(jiān)聽網(wǎng)絡(luò)讀事件
                                key.interestOps(SelectionKey.OP_READ);
                                // 向服務(wù)端發(fā)送數(shù)據(jù)
                                channel.write(ByteBuffer.wrap("hello,I'm client".getBytes()));
                            }else {
                                key.cancel();
                            }
                            // 4. 如果有數(shù)據(jù)需要讀取
                        }else if(key.isReadable()){
                            ByteBuffer byteBuffer = ByteBuffer.allocate(128);
                            // 把數(shù)據(jù)寫入 buffer
                            channel.read(byteBuffer);
                            byteBuffer.flip();
                            // 把數(shù)據(jù)讀出來。
                            String response = StandardCharsets.UTF_8.decode(byteBuffer).toString();
                            System.out.println("["+Thread.currentThread().getName()+"] receive response:"+response);
                            Thread.sleep(5000);
                            // 向服務(wù)端發(fā)送數(shù)據(jù)
                            channel.write(ByteBuffer.wrap("hello".getBytes()));
                        }
                    }
                }
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if(channel != null){
                    try{
                        channel.close();
                    }catch (Exception e){
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

// 1.打開服務(wù)端
serverSocketChannel = ServerSocketChannel.open();
// 配置為非阻塞IO
serverSocketChannel.configureBlocking(false);
// 設(shè)置端口，
serverSocketChannel.socket().bind(new InetSocketAddress(9000),100);
// 打開 多路復(fù)用選擇器
selector = Selector.open();
// 2.把 serverSocketChannel 注冊到 selector 上。 監(jiān)聽 serverSocketChannel 的連接請求事件，與各個(gè)客戶端建立連接請求
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

public static Selector open() throws IOException {
    return SelectorProvider.provider().openSelector();
}