static final ClosedChannelException CLOSED_CHANNEL_EXCEPTION = new ClosedChannelException();...static {CLOSED_CHANNEL_EXCEPTION.setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);NOT_YET_CONNECTED_EXCEPTION.setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);}...@Overridepublic void write(Object msg, ChannelPromise promise) {ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;if (outboundBuffer == null) {// If the outboundBuffer is null we know the channel was closed and so// need to fail the future right away. If it is not null the handling of the rest// will be done in flush0()// See https://github.com/netty/netty/issues/2362
                safeSetFailure(promise, CLOSED_CHANNEL_EXCEPTION);// release message now to prevent resource-leak
                ReferenceCountUtil.release(msg);return;}outboundBuffer.addMessage(msg, promise);}

    public static void main(String[] args) throws IOException, InterruptedException {Bootstrap b = new Bootstrap();b.group(new NioEventLoopGroup()).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {}});b.connect("localhost", 8090).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (future.isSuccess()) {future.channel().write(Unpooled.buffer().writeBytes("123".getBytes()));future.channel().flush();}}});

public class SimpleServer {public static void main(String[] args) throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup(1);EventLoopGroup workerGroup = new NioEventLoopGroup();ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_REUSEADDR, true).childHandler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {ch.pipeline().addLast(new SimpleServerHandler());}});b.bind(8090).sync().channel().closeFuture().sync();}
}public class SimpleServerHandler extends ChannelInboundHandlerAdapter {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {ctx.channel().close().sync();}@Overridepublic void channelRead(ChannelHandlerContext ctx, final Object msg) throws Exception {System.out.println(123);}@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {System.out.println("inactive");}
}

private static void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {final NioUnsafe unsafe = ch.unsafe();if (!k.isValid()) {// close the channel if the key is not valid anymore
            unsafe.close(unsafe.voidPromise());return;}try {int readyOps = k.readyOps();// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead// to a spin loopif ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {unsafe.read();if (!ch.isOpen()) {// Connection already closed - no need to handle write.
                    return;}}if ((readyOps & SelectionKey.OP_WRITE) != 0) {// Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write
                ch.unsafe().forceFlush();}if ((readyOps & SelectionKey.OP_CONNECT) != 0) {// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking// See https://github.com/netty/netty/issues/924int ops = k.interestOps();ops &= ~SelectionKey.OP_CONNECT;k.interestOps(ops);unsafe.finishConnect();}} catch (CancelledKeyException e) {unsafe.close(unsafe.voidPromise());}}

public class SimpleClient {private static final Logger logger = LoggerFactory.getLogger(SimpleClient.class);public static void main(String[] args) throws IOException, InterruptedException {Bootstrap b = new Bootstrap();b.group(new NioEventLoopGroup()).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {}});b.connect("localhost", 8090).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (future.isSuccess()) { future.channel().close();future.channel().write(Unpooled.buffer().writeBytes("123".getBytes())).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (!future.isSuccess()) {logger.error("Error", future.cause());}}});future.channel().flush();}}});}
}

public class SimpleClient {private static final Logger logger = LoggerFactory.getLogger(SimpleClient.class);public static void main(String[] args) throws IOException, InterruptedException {Bootstrap b = new Bootstrap();b.group(new NioEventLoopGroup()).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {}});Channel channel = b.connect("localhost", 8090).sync().channel();Thread.sleep(3000);channel.writeAndFlush(Unpooled.buffer().writeBytes("123".getBytes())).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (!future.isSuccess()) {logger.error("error", future.cause());}}});}
}

public class SimpleServer {public static void main(String[] args) throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup(1);EventLoopGroup workerGroup = new NioEventLoopGroup();ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_REUSEADDR, true).childHandler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {ch.pipeline().addLast(new SimpleServerHandler());}});b.bind(8090).sync().channel().closeFuture().sync();}
}