> For the complete documentation index, see [llms.txt](https://jupiter-1992.gitbook.io/jupiter-note/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jupiter-1992.gitbook.io/jupiter-note/hou-duan/netty/02-netty-server.md). # 02 Netty Server Netty 是一个提供了易于使用的 API 客户端/服务器框架。特性： * 高并发 - NIO（非阻塞 IO） * 传输快 - 零拷贝 Netty 服务器流程： * 构建一对主从线程组 * 定义服务器启动类 * 为服务器设置 Channel * 设置处理从线程池的助手类初始化器 * 监听启动和关闭服务器 ![channel 初始化器](https://raw.githubusercontent.com/chanshiyucx/yoi/master/2019/Netty-服务器/11_channel_初始化器.png) ## Netty Server ```java @Component public class WSServer { private EventLoopGroup mainGroup; private EventLoopGroup subGroup; private ServerBootstrap server; private ChannelFuture channelFuture; private static class SingletionWSServer { static final WSServer instance = new WSServer(); } public static WSServer getInstance() { return SingletionWSServer.instance; } public WSServer() { // 主线程组，用于接收客户端连接，不做任何处理 mainGroup = new NioEventLoopGroup(); // 从线程组，专门处理主线程组的任务 subGroup = new NioEventLoopGroup(); // netty 服务器 server = new ServerBootstrap(); server.group(mainGroup, subGroup) // 设置主从线程组 .channel(NioServerSocketChannel.class) // 设置 nio 的双向通道 .childHandler(new WSServerInitializer()); // 子处理器，用于处理 subGroup } public void start() { this.channelFuture = server.bind(8088); System.out.println("netty websocket server 启动完毕..."); } } ``` ## Netty Server Initializer ```java public class WSServerInitializer extends ChannelInitializer { @Override protected void initChannel(NioSocketChannel nioSocketChannel) throws Exception { // 通过 SocketChannel 去获得对应的管道，通过管道添加 handler ChannelPipeline pipeline = nioSocketChannel.pipeline(); /** * ========================================================================== * 以下用于支持 http 协议 * ========================================================================== */ // HttpServerCodec 是由 netty 提供的助手类，可以理解为拦截器，当请求到服务端做解码，响应到客户端做编码 // websocket 基于 http 协议，所以要有 http 编解码器 pipeline.addLast(new HttpServerCodec()); // 对写大数据流的支持 pipeline.addLast(new ChunkedWriteHandler()); // 对 httpMessage 进行聚合，聚合成 FullHttpRequest 或 FullHttpResponse，几乎在 netty 中的编程，都会使用到此 handler pipeline.addLast(new HttpObjectAggregator(1024*64)); /** * ============================================================================ * websocket 服务器处理协议 * 对于 websokcet 来讲，都是以 frames 进行传输的，不同的数据类型对应不同的 frames 也不同 * ============================================================================ */ pipeline.addLast(new WebSocketServerProtocolHandler("/ws")); pipeline.addLast(new ChatHandler()); // 消息测试 } } ``` ## ChatHandler ```java public class ChatHandler extends SimpleChannelInboundHandler { // 用于记录和管理所有客户端的 channel private static ChannelGroup clients = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE); @Override protected void channelRead0(ChannelHandlerContext channelHandlerContext, TextWebSocketFrame textWebSocketFrame) throws Exception { // 获取客户端传输过来的消息 String content = textWebSocketFrame.text(); System.out.println("接受数据消息：" + content); // 此方法给全部 channel 刷入消息 clients.writeAndFlush(new TextWebSocketFrame("[接收消息" + LocalDateTime.now() + "] " + content)); } /** * 当客户端连接服务器之后（打开连接） * 获取客户端的 channel，并且放到 ChannelGroup 中去管理 * @param ctx * @throws Exception */ @Override public void handlerAdded(ChannelHandlerContext ctx) throws Exception { clients.add(ctx.channel()); } @Override public void handlerRemoved(ChannelHandlerContext ctx) throws Exception { // 当触发 handlerRemoved 时，ChannelGroup 会自动移除对应客户端的 channel，无需手动移除 // clients.remove(ctx.channel()); System.out.println("客户端断开连接，channel 对应的长 id 为：" + ctx.channel().id().asLongText()); } } ``` ## Netty Booter ```java @Component public class NettyBooter implements ApplicationListener { @Override public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) { if (contextRefreshedEvent.getApplicationContext().getParent() == null) { try { WSServer.getInstance().start(); } catch (Exception e) { e.printStackTrace(); } } } } ``` ## 概念 ### ChannelInboundHandlerAdapter vs SimpleChannelInboundHandler `SimpleChannelInboundHandler是有泛型参数的`，可以指定一个具体的类型参数，通过 decoder 配合使用，非常方便。`ChannelInboundHandlerAdapter` 则是直接操作 byte 数组的。 类的关系： ```java ChannelInboundHandlerAdapter extends ChannelHandlerAdapter implements ChannelInboundHandler SimpleChannelInboundHandler extends ChannelInboundHandlerAdapter ``` 可以看出 `SimpleChannelInboundHandler` 是继承 `ChannelInboundHandlerAdapter` 的，也就是说 `SimpleChannelInboundHandler` 也拥有 `ChannelInboundHandlerAdapter` 的方法。 一般而言业务代码 `SimpleChannelInboundHandler` 写在 `channelRead0` 方法中，而 `ChannelInboundHandlerAdapter` 写在 `channelRead` 方法中，注意后面有 0 后缀区别。 **`SimpleChannelInboundHandler` 对 `channelRead` 的重写：** ```java public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { boolean release = true; try { if (acceptInboundMessage(msg)) { //类型匹配 I imsg = (I) msg; channelRead0(ctx, imsg); } else { release = false; ctx.fireChannelRead(msg); } } finally { if (autoRelease && release) { ReferenceCountUtil.release(msg); //释放引用 } } } ``` `SimpleChannelInboundHandler` 的 `channelRead` 相比 `ChannelInboundHandlerAdapter` 而言，主要做了类型匹配以及用完之后释放指向保存该消息的 ByteBuf 的内存引用。 如果说 channelRead 都是同步操作的话，`SimpleChannelInboundHandler` 是不错的选择，如果操作是异步的话，那他的逻辑就有点麻烦了，例如你把数据交给另外的线程处理了，还没处理就会释放了，这时候 `ChannelInboundHandlerAdapter` 处理自由的优点也就提现出来了，可以更好的处理更多的特定场景。 `SimpleChannelInboundHandler` 的好处是可以处理不同的类型对象，并且可以做释放。`ChannelInboundHandlerAdapter` 的好处则是更自由，在异步的场景下更适合。 参考文章：\ [从零开始学 netty](https://www.imooc.com/article/27677) --- # Agent Instructions This documentation is published with GitBook. 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