Netty

Server

// 把 NettyServer 的创建交给 Spring 管理
@Component
public class NettyServer {

    private Logger logger = LoggerFactory.getLogger(getClass());

    @Value("${netty.port}")
    private Integer port;

    @Resource
    private NettyServerHandlerInitializer nettyServerHandlerInitializer;

    // boss 线程组，用于服务端接受客户端的连接
    private EventLoopGroup bossGroup = new NioEventLoopGroup();
  
    // worker 线程组，用于服务端接受客户端的数据读写
    private EventLoopGroup workerGroup = new NioEventLoopGroup();
  
    // Netty Server Channel
    private Channel channel;

    // 启动 Netty Server
    @PostConstruct
    public void start() throws InterruptedException {
        // 创建 ServerBootstrap 对象，用于 Netty Server 启动
        ServerBootstrap bootstrap = new ServerBootstrap();
        // 设置 ServerBootstrap 的各种属性
      	// 设置两个 EventLoopGroup 对象
        bootstrap.group(bossGroup, workerGroup)
          			// 指定 Channel 为服务端 NioServerSocketChannel
                .channel(NioServerSocketChannel.class)
          			// 设置 Netty Server 的端口
                .localAddress(new InetSocketAddress(port)) 
          			// 服务端 accept 队列的大小
                .option(ChannelOption.SO_BACKLOG, 1024) 
          			// TCP Keepalive 机制，实现 TCP 层级的心跳保活功能
                .childOption(ChannelOption.SO_KEEPALIVE, true) 
          			// 允许较小的数据包的发送，降低延迟
                .childOption(ChannelOption.TCP_NODELAY, true)
          			// 处理器
                .childHandler(nettyServerHandlerInitializer);
        // 绑定端口，并同步等待成功，即启动服务端
        ChannelFuture future = bootstrap.bind().sync();
        if (future.isSuccess()) {
            channel = future.channel();
            logger.info("[start][Netty Server 启动在 {} 端口]", port);
        }
    }

    // 关闭 Netty Server
    @PreDestroy
    public void shutdown() {
        // 关闭 Netty Server
        if (channel != null) {
            channel.close();
        }
        // <3.2> 优雅关闭两个 EventLoopGroup 对象
        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();
    }

}

NettyServerHandlerInitializer

@Component
public class NettyServerHandlerInitializer extends ChannelInitializer<Channel> {

    /**
     * 心跳超时时间
     */
    private static final Integer READ_TIMEOUT_SECONDS = 3 * 60;
  
    @Resource
    private NettyServerHandler nettyServerHandler;

    @Override
    protected void initChannel(Channel ch) {
        // 获得 Channel 对应的 ChannelPipeline
        ChannelPipeline channelPipeline = ch.pipeline();
        // 添加一堆 NettyServerHandler 到 ChannelPipeline 中
        channelPipeline
                // 空闲检测
                .addLast(new ReadTimeoutHandler(READ_TIMEOUT_SECONDS, TimeUnit.SECONDS))
                // 编码器
                .addLast(new InvocationEncoder())
                // 解码器
                .addLast(new InvocationDecoder())
                // 消息分发器
                .addLast(messageDispatcher)
                // 服务端处理器
                .addLast(nettyServerHandler)
        ;
    }

}