寫個簡單點，比較小白的文檔，言語比較接地氣

Netty是什么？

NIO的高層封裝，NIO很難寫，所以有了Netty，方便異步的操作

service的主要代碼片段

public void run() throws Exception {

EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)

EventLoopGroup workerGroup = new NioEventLoopGroup();

try {

ServerBootstrap b = new ServerBootstrap(); // (2)

b.group(bossGroup, workerGroup)

.channel(NioServerSocketChannel.class) // (3)

.childHandler(new ChannelInitializer() { // (4)

@Override

public void initChannel(SocketChannel ch) throws Exception {

ch.pipeline().addLast(new DiscardServerHandler());

}

})

.option(ChannelOption.SO_BACKLOG, 128) // (5)

.childOption(ChannelOption.SO_KEEPALIVE, true); // (6)

// Bind and start to accept incoming connections.

ChannelFuture f = b.bind(port).sync(); // (7)

// Wait until the server socket is closed.

// In this example, this does not happen, but you can do that to gracefully

// shut down your server.

f.channel().closeFuture().sync();

} finally {

workerGroup.shutdownGracefully();

bossGroup.shutdownGracefully();

}

}

按照代碼順序解釋如下

(1) EventLoopGroup bossGroup = new NioEventLoopGroup();

事件循環隊列，用來接受或發送事件。大家可以把他想象成郵局，消息都要先到郵局，然后再分發出去，郵局維護了一個循環隊列，用來不斷的收信和發信。

(2)ServerBootstrap b = new ServerBootstrap();

啟動服務

(3) b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)

開啟了一個通道，這個通道是用來接受連接請求的，管道大家都知道吧，IO里也有，NIO中也有，一切Java中到處都是管道

(4).childHandler(new ChannelInitializer()

這個handler是用來表示響應什么樣的事件的，比如我們這里DiscardServerHandler，隨著程序的復雜，你會加上更多的handle，handler是具體干事的人

(5).option(ChannelOption.SO_BACKLOG, 128)

channel的配置參數，具體可以查手冊

(6).childOption(ChannelOption.SO_KEEPALIVE, true);

option()是 NioServerSocketChannel的配置，childOption()是被parent ServerChannel接受的channel，這里就指的是NioServerSocketChannel

(7)ChannelFuture f = b.bind(port).sync();

綁定端口并開始

再看看我們主要進行事件處理的handle

public class DiscardServerHandler extends ChannelHandlerAdapter { // (1)

@Override

public void channelRead(ChannelHandlerContext ctx, Object msg) { // (2)

// Discard the received data silently.

((ByteBuf) msg).release(); // (3)

}

@Override

public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { // (4)

// Close the connection when an exception is raised.

cause.printStackTrace();

ctx.close();

}

}

(1)DiscardServerHandler extends ChannelHandlerAdapter

表示：俺是具體干事的人

(2)我們overrider了 channelRead()，用來讀取接受到的信息

(3)異常處理，懂的...