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之前的一片文章里面总结了一下IO模型的演进（BIO、NIO、Netty演化总结-CSDN博客），里面给了一个示例AsyncNonBlockingServerWithThreadPool，最近想了想，发现这个代码跟netty的模型还是有一些出入，说是netty的雏形好像有点牵强，于是想了一下，还是决定写一个更接近netty的极简版代码，仅供交流，有不对的地方欢迎指正，不喜勿喷，直接上代码
public class MyBossGroup {//多路复用器private Selector selector;private ServerSocketChannel serverChannel;//读写处理线程（对应netty里面的worker线程组）private MyWorkerGroup[] myWorkerGroups = new MyWorkerGroup[10];//计数器，用于从线程组中挑选一个线程来处理事件private final AtomicLong idx = new AtomicLong();public MyBossGroup(int port) throws IOException {// 创建选择器和服务器通道selector = Selector.open();serverChannel = ServerSocketChannel.open();serverChannel.bind(new InetSocketAddress(port));serverChannel.configureBlocking(false);// 注册服务器通道到选择器，并注册接收连接事件serverChannel.register(selector, SelectionKey.OP_ACCEPT);for (int i = 0; i < myWorkerGroups.length; i++) {myWorkerGroups[i] = new MyWorkerGroup();}}public void start() throws IOException {System.out.println("Server started.");while (true) {// 阻塞等待事件发生selector.select();// 处理连接事件Iterator<SelectionKey> keyIterator = selector.selectedKeys().iterator();while (keyIterator.hasNext()) {SelectionKey key = keyIterator.next();keyIterator.remove();// 接收连接事件handleAccept(key);}}}private void handleAccept(SelectionKey key) throws IOException {ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();SocketChannel clientChannel = serverChannel.accept();clientChannel.configureBlocking(false);//挑选一个线程，将clientChannel绑定到这个线程中去MyWorkerGroup myWorkerGroup = myWorkerGroups[(int) Math.abs(idx.getAndIncrement() % myWorkerGroups.length)];//已经建立连接的socket交给worker线程组myWorkerGroup.register(clientChannel);System.out.println("New client connected: " + clientChannel.getRemoteAddress());}public static void main(String[] args) {try {MyBossGroup server = new MyBossGroup(8080);server.start();} catch (IOException e) {e.printStackTrace();}}
}这个MyBossGroup就是我们在编写netty应用程序的时候的bossgroup的核心逻辑，负责接收客户端连接，并且将连接的socket注册到worker线程组中，下面的MyWorkerGroup就是编写netty应用程序的时候的workergroup的核心逻辑，负责数据的读写：
public class MyWorkerGroup {private Selector selector;private Thread thread;private ByteBuffer buffer;public MyWorkerGroup() {try {selector = Selector.open();} catch (IOException e) {e.printStackTrace();}thread = new Thread(new MyRunnable());buffer = ByteBuffer.allocate(1024);}class MyRunnable implements Runnable {@Overridepublic void run() {while (true) {try {selector.select();// 处理连接事件Iterator<SelectionKey> keyIterator = selector.selectedKeys().iterator();while (keyIterator.hasNext()) {SelectionKey key = keyIterator.next();keyIterator.remove();SocketChannel clientChannel = (SocketChannel) key.channel();if (key.isReadable()) {buffer.clear();int bytesRead = 0;try {bytesRead = clientChannel.read(buffer);} catch (IOException e) {e.printStackTrace();closeSocketChannel(key, clientChannel);continue;}if (bytesRead == -1) {closeSocketChannel(key, clientChannel);try {System.out.println("Client disconnected: " + clientChannel.getRemoteAddress());} catch (IOException e) {e.printStackTrace();}continue;}buffer.flip();byte[] data = new byte[buffer.remaining()];buffer.get(data);System.out.println("Received message from client: " + new String(data));clientChannel.write(ByteBuffer.wrap((new String("server_response:") + new String(data)).getBytes()));System.err.println("current_thread:" + thread.getName());} else {closeSocketChannel(key, clientChannel);}}} catch (Exception e) {e.printStackTrace();}}}private void closeSocketChannel(SelectionKey key, SocketChannel socketChannel) {try {System.out.println("Client disconnected: " + socketChannel.getRemoteAddress());// 客户端关闭连接key.cancel();socketChannel.close();} catch (IOException e) {e.printStackTrace();}}}public void register(SocketChannel socketChannel) {//这里唤醒是因为当连接数量超过myWorkerGroups数组长度的时候，可能会因为selector.select()阻塞，导致下面的register方法无法运行selector.wakeup();try {socketChannel.register(selector, SelectionKey.OP_READ);} catch (ClosedChannelException e) {e.printStackTrace();}if (!thread.isAlive()) {thread.start();}}
}可以看到两个group其核心逻辑都是一个死循环，监听selector里面的事件，只是在netty里面将这两个死循环合并到了一个类里面，也就是NioEventLoop的run方法，每一个NioEventLoop独立维护一个自己的selector和任务队列（在这里没有体现），客户端连接第一次连接过来的socket绑定到一个NioEventLoop之后，后面这个socket的读写事件就全部由这个NioEventLoop负责，这样就有几个好处：
1、selector.select是一个阻塞的方法，由于每一个workergroup独立维护自己的selector，不会相互影响
2、每一个连接的客户端在绑定workergroup的时候实际上就是绑定了一个selector，这样每一个workergroup所负责管理的客户端连接的socket之间也相互不影响
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