使用netty进行服务端网络编程及数据高效分发功能实现

       这篇文章起了一个很牛b的名字，实际要讲的内容很简单。但是还是发现很多人把这个功能写复杂了。netty的服务端网络编程，按照官方提供的demo，稍加修改即可，但是一些参数选项，需要自己去完善设置。而数据分发功能，就是面向所有连接分发数据，很多人的做法是使用java concurrent包下的相关容器保存连接，然后需要分发数据时，遍历集合中的元素，一个一个的调用writeAndFlush()将数据发出去。其实可以更简单一些，使用线程安全的ChannelGroup保存连接并分发数据。性能提高多少，我没有对比过，至少代码看着简化了。下面是相关实现代码，实际生产环境中，下面代码应该还有很多很多需要优化的地方，目前我还没有在超过10k并发连接情况下测试过下面的代码。

public class NetServer implements Runnable {

    private static Logger LOGGER = LoggerFactory.getLogger(NetServer.class);
    private final static int PORT = 9500;
    private final static int MAX_MESSAGE_LENGTH = 8192;
    private final ChannelGroup channels_ = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    public NetServer() {
    }

    // 分发数据
    public void dispatcher(String message) {
        channels_.writeAndFlush(message);
    }

    @Override
    public void run() {
        startup();
    }

    private void startup() {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup);
            b.channel(NioServerSocketChannel.class);
            b.option(ChannelOption.SO_BACKLOG, 128);
            b.option(ChannelOption.TCP_NODELAY, true);
            b.childHandler(new ChannelInitializer() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ChannelPipeline p = ch.pipeline();

                    p.addLast(new LengthFieldBasedFrameDecoder(MAX_MESSAGE_LENGTH, 0, 4, 0 ,4));
                    p.addLast(new LengthFieldPrepender(4));
                    p.addLast(new StringDecoder(CharsetUtil.UTF_8));
                    p.addLast(new StringEncoder(CharsetUtil.UTF_8));
                    p.addLast(new NetServerHandler(channels_));
                }
            });

            ChannelFuture future = b.bind(PORT).sync();
            future.addListener(new GenericFutureListener>() {
                @Override
                public void operationComplete(Future future) throws Exception {
                    if (future.isSuccess()) {
                        LOGGER.info("服务器启动成功...");
                    } else {
                        LOGGER.info("服务器启动失败...");
                        if (future.cause() != null) {
                            LOGGER.error("异常信息: " + future.cause().getMessage());
                        }
                    }
                }
            });

            future.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            LOGGER.error("服务器启动出现异常..." + e.getMessage());
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

}

public class NetServerHandler extends SimpleChannelInboundHandler {

    private ChannelGroup channels_;
    private static Logger LOGGER = LoggerFactory.getLogger(NetServerHandler.class);

    public NetServerHandler(ChannelGroup channels) {
        channels_ = channels;
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        channels_.add(ctx.channel());
        LOGGER.info("{} is up...当前连接数量: {}", ctx.channel().remoteAddress(), channels_.size());
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        ctx.close();
        LOGGER.info("{} is down...当前连接数量: {}", ctx.channel().remoteAddress(), channels_.size());
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
        LOGGER.error("与客户端 {} 连接出现异常, 异常信息: " + cause.getMessage(), ctx.channel().remoteAddress());
    }

}