gistfile1.java

public static void main(String[] args) throws Exception {
    // Configure the server.
    ServerBootstrap b = new ServerBootstrap();
    try {
        b.group(new NioEventLoopGroup(), new NioEventLoopGroup())
         .channel(new NioServerSocketChannel())
         .option(ChannelOption.SO_BACKLOG, 100)
         .localAddress(8080)
         .childOption(ChannelOption.TCP_NODELAY, true)
         .childHandler(new ChannelInitializer<SocketChannel>() {
             @Override
             public void initChannel(SocketChannel ch) throws Exception {
                 ch.pipeline().addLast(handler1, handler2, ...);
             }
         });

        // Start the server.
        ChannelFuture f = b.bind().sync();

        // Wait until the server socket is closed.
        f.channel().closeFuture().sync();
    } finally {
        // Shut down all event loops to terminate all threads.
        b.shutdown();
    }
}

Line 6 should be ".channel(NioServerSocketChannel.class)" since 4.0.0.Alpha4.
Cf. https://netty.io/Blog/Netty+400Alpha4+is+out