本文共 3942 字，大约阅读时间需要 13 分钟。

前言

上一篇博文中主要介绍了三种IO模式，Netty是一个高性能、异步事件驱动的Java NIO框架，本文以一个简单的Netty程序带领大家先来领略一下Netty的风采，程序的功能主要是获取当前的服务器时间。

客户端

TimeClient.java

public class TimeClient {    public void connect(int port, String host) throws Exception{        EventLoopGroup group = new NioEventLoopGroup();        try {            Bootstrap b = new Bootstrap();            b.group(group).channel(NioSocketChannel.class)                    .option(ChannelOption.TCP_NODELAY, true)                    .handler(new ChannelInitializer
   
    () {                        @Override                        public void initChannel(SocketChannel ch) throws Exception{                            ch.pipeline().addLast(new TimeClientHandler());                        }                    });            ChannelFuture f = b.connect(host, port).sync();            f.channel().closeFuture().sync();        }finally {            group.shutdownGracefully();        }    }    public static void main(String[] args) throws Exception{        int port = 8800;        new TimeClient().connect(port, "localhost");    }}
   

TimeClientHandler.java

public class TimeClientHandler extends ChannelHandlerAdapter {
       private final ByteBuf firstMessage;    public TimeClientHandler(){        byte[] req = "QUERY TIME ORDER".getBytes();        firstMessage = Unpooled.buffer(req.length);        firstMessage.writeBytes(req);    }    public void channelActive(ChannelHandlerContext ctx){        ctx.writeAndFlush(firstMessage);    }    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{        ByteBuf buf = (ByteBuf)msg;        byte[] req = new byte[buf.readableBytes()];        buf.readBytes(req);        String body = new String(req, "UTF-8");        System.out.println("Now is : " + body);    }    public void exceptionCaught(ChannelHandlerContext ctx) throws Exception{        ctx.close();    }}

服务端

TimeServer.java

public class TimeServer {
       public void bind(int port) throws Exception{        EventLoopGroup bossGroup = new NioEventLoopGroup();        EventLoopGroup workerGroup = new NioEventLoopGroup();        try {            ServerBootstrap b = new ServerBootstrap();            b.group(bossGroup, workerGroup)                    .channel(NioServerSocketChannel.class)                    .option(ChannelOption.SO_BACKLOG, 1024)                    .childHandler(new ChannelInitializer
   
    (){                        @Override                        protected void initChannel(SocketChannel ch) throws Exception {                            ch.pipeline().addLast(new TimeServerHandler());                        }                    });            ChannelFuture f = b.bind(port).sync();            f.channel().closeFuture().sync();        }finally {            bossGroup.shutdownGracefully();            workerGroup.shutdownGracefully();        }    }    public static void main(String[] args) throws Exception{        int port = 8800;        new TimeServer().bind(port);    }}
   

TimeServerHandler.java

public class TimeServerHandler extends ChannelHandlerAdapter {
       public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{        ByteBuf buf = (ByteBuf)msg;        byte[] req = new byte[buf.readableBytes()];        buf.readBytes(req);        String body = new String(req, "UTF-8");        System.out.println("The time server receive order : " + body);        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)?new Date(System.currentTimeMillis()).toString() : "BAD ORDER";        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());        ctx.write(resp);    }    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception{        ctx.flush();    }    public void exceptionCaught(ChannelHandlerContext ctx) throws Exception{        ctx.close();    }}

运行结果

客户端

总结

“蚊子虽小，五脏俱全”。上述代码功能虽然简单，但是却涵盖了例如Channel、ChannelPipeline、EventLoopGroup、EventLoopGroup等Netty最核心的组件，这些核心组件会在后续的博文中详细讲述。