Netty学习之理解selector原理示例

public class BioServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(9000);
        // 任务处理线程池
        ExecutorService pool = Executors.newFixedThreadPool(10);
        while (true) {
            System.out.println("server start");
            //阻塞方法等待客户端连接
            Socket clientSocket = serverSocket.accept();
            System.out.println("new client");
            pool.execute(()->{
                handler(clientSocket);
            });
        }
    }
    private static void handler(Socket clientSocket) {
        try {
            byte[] bytes = new byte[1024];
            System.out.println("reading");
            //接收客户端的数据，阻塞方法，没有数据可读时就阻塞
            int read = clientSocket.getInputStream().read(bytes);
            System.out.println("read over");
            if (read != -1) {
                System.out.println("received data：" + new String(bytes, 0, read));
            }
            clientSocket.getOutputStream().write("HelloClient".getBytes());
            clientSocket.getOutputStream().flush();
        } catch (Exception e) {
        }
    }
}

public class NioServer {
    public static void main(String[] args) throws IOException, InterruptedException {
        // 创建NIO ServerSocketChannel
        ServerSocketChannel serverSocket = ServerSocketChannel.open();
        serverSocket.socket().bind(new InetSocketAddress(9000));
        serverSocket.configureBlocking(false);
        // 打开Selector处理Channel，底层调用epoll_create
        Selector selector = Selector.open();
        // 把ServerSocketChannel注册到selector上，并且selector对客户端accept连接操作感兴趣，底层调用epoll_ctl
        serverSocket.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("服务启动成功");
        while (true) {
            // 阻塞等待需要处理的事件发生，即调用epoll_wait
            selector.select();
            // 获取selector中注册的全部事件的 SelectionKey 实例
            Set<SelectionKey> selectionKeys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = selectionKeys.iterator();
            // 遍历SelectionKey对事件进行处理
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                // 如果是OP_ACCEPT事件，则进行连接获取和事件注册
                if (key.isAcceptable()) {
                    ServerSocketChannel server = (ServerSocketChannel) key.channel();
                    SocketChannel socketChannel = server.accept();
                    socketChannel.configureBlocking(false);
                    // 这里只注册了读事件，如果需要给客户端发送数据可以注册写事件，底层调用epoll_ctl
                    socketChannel.register(selector, SelectionKey.OP_READ);
                    System.out.println("客户端连接成功");
                } else if (key.isReadable()) {  // 如果是OP_READ事件，则进行读取和打印
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    ByteBuffer byteBuffer = ByteBuffer.allocate(128);
                    int len = socketChannel.read(byteBuffer);
                    // 如果有数据，把数据打印出来
                    if (len > 0) {
                        System.out.println("接收到消息：" + new String(byteBuffer.array()));
                    } else if (len == -1) { // 如果客户端断开连接，关闭Socket
                        System.out.println("客户端断开连接");
                        socketChannel.close();
                    }
                }
                //从事件集合里删除本次处理的key，防止下次select重复处理
                iterator.remove();
            }
        }
    }
}