Netty官网：https://netty.io/
Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients.
Java技术栈方向的朋友应该或多或少都听说过Netty是对Java中nio ( Non Blocking IO )的封装，让我们能快速开发出性能更高、扩展性更好的网络应用程序。那么Netty究竟对nio做了怎样的封装呢？本文主要从源码角度揭开这层面纱。
源码追踪中，我使用阿里的语雀产品的思维图记录主要方法调用，上面的图片是部分截图，完整原貌见：
预备知识在初探Netty源码之前，至少需要理解Reactor Pattern、java.nio基本使用、Netty基本使用，这样后面才能把Netty的源码与java.nio对比着来看。
Reactor Pattern不识Netty真面目，只缘未读此真经。Doug Lea (java.util.concurrent包的作者) 在《Scalable IO in Java》中循序渐进地分析了如何构建可伸缩的高性能IO服务以及服务模型的演变与进化。文中描述的Reactor Pattern，也被Netty等大多数高性能IO服务框架所借鉴。因此仔细阅读《Scalable IO in Java》有助于更好地理解Netty框架的架构与设计。详情见：
传统的服务模式Server端为每一个Client端的连接请求都开启一个独立线程，也就是所谓的BIO (Blocking IO)，即java.net.ServerSocket包下api的使用。
Reactor responds to IO events by dispatching the appropriate handler (Similar to AWT thread)
Handlers perform non-blocking actions (Similar to AWT ActionListeners)
Manage by binding handlers to events (Similar to AWT addActionListener)
(1) 单线程版本
(2) 多线程版本
(3) 多Reactor版本 (一主多从、多主多从)
Netty正是借鉴了这种多Reactor版本的设计。 快速上手java.nio
Channels：Connections to files, sockets etc that support non-blocking reads
Buffers：Array-like objects that can be directly read or written by Channels
Selectors：Tell which of a set of Channels have IO events
SelectionKeys：Maintain IO event status and bindings
注意：以下Demo仅专注于主逻辑，没有处理异常，也没有关闭资源。
Server端 import java.io.IOException; import java.net.InetSocketAddress; import java.nio.ByteBuffer; import java.nio.channels.SelectionKey; import java.nio.channels.Selector; import java.nio.channels.ServerSocketChannel; import java.nio.channels.SocketChannel; import java.nio.channels.spi.SelectorProvider; import java.util.Iterator; public class NIOServer { private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider(); public static void main(String[] args) throws IOException { // ServerSocketChannel.open() ServerSocketChannel serverSocketChannel = DEFAULT_SELECTOR_PROVIDER.openServerSocketChannel(); serverSocketChannel.configureBlocking(false); serverSocketChannel.socket().bind(new InetSocketAddress(8080)); // Selector.open() Selector selector = DEFAULT_SELECTOR_PROVIDER.openSelector(); // register this serverSocketChannel with the selector serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT); // selector.select() while (!Thread.interrupted()) { selector.select(); Iterator<SelectionKey> it = selector.selectedKeys().iterator(); while (it.hasNext()) { SelectionKey key = it.next(); it.remove(); // handle IO events handle(key); } } } private static void handle(SelectionKey key) throws IOException { if (key.isAcceptable()) { ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel(); SocketChannel socketChannel = serverSocketChannel.accept(); socketChannel.configureBlocking(false); socketChannel.register(key.selector(), SelectionKey.OP_READ); } else if (key.isReadable()) { SocketChannel socketChannel = (SocketChannel) key.channel(); // read client data ByteBuffer buffer = ByteBuffer.allocate(1024); int len = socketChannel.read(buffer); if (len != -1) { String msg = String.format("recv client[%s] data：%s", socketChannel.getRemoteAddress(), new String(buffer.array(), 0, len)); System.out.println(msg); } // response client ByteBuffer data = ByteBuffer.wrap("Hello, NIOClient!".getBytes()); socketChannel.write(data); key.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE); } else if (key.isWritable()) { // ... } } } Client端 import java.io.IOException; import java.net.InetSocketAddress; import java.nio.ByteBuffer; import java.nio.channels.SelectionKey; import java.nio.channels.Selector; import java.nio.channels.SocketChannel; import java.nio.channels.spi.SelectorProvider; import java.util.Iterator; public class NIOClient { private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider(); public static void main(String[] args) throws IOException { // SocketChannel.open() SocketChannel socketChannel = DEFAULT_SELECTOR_PROVIDER.openSocketChannel(); socketChannel.configureBlocking(false); socketChannel.connect(new InetSocketAddress("127.0.0.1", 8080)); // Selector.open() Selector selector = DEFAULT_SELECTOR_PROVIDER.openSelector(); // register this socketChannel with the selector socketChannel.register(selector, SelectionKey.OP_CONNECT); // selector.select() while (!Thread.interrupted()) { selector.select(); Iterator<SelectionKey> it = selector.selectedKeys().iterator(); while (it.hasNext()) { SelectionKey key = it.next(); it.remove(); // handle IO events if (key.isConnectable()) { SocketChannel channel = (SocketChannel) key.channel(); if (channel.isConnectionPending()) { channel.finishConnect(); } channel.configureBlocking(false); // request server ByteBuffer buffer = ByteBuffer.wrap("Hello, NIOServer!".getBytes()); channel.write(buffer); channel.register(selector, SelectionKey.OP_READ); } else if (key.isReadable()) { SocketChannel channel = (SocketChannel) key.channel(); // read server data ByteBuffer buffer = ByteBuffer.allocate(1024); int len = channel.read(buffer); if (len != -1) { String msg = String.format("recv server[%s] data：%s", channel.getRemoteAddress(), new String(buffer.array(), 0, len)); System.out.println(msg); } } } } } } 快速上手Netty更多官方example，请参考：