Server与Client建立连接后，会执行以下的步骤： 1、Client向Server发送消息：Are you ok? 2、Server接收客户端发送的消息，并打印出来。 3、Server端向客户端发送消息：I am ok! 4、Client接收Server端发送的消息，并打印出来，通讯结束。 涉及到的类有4个： 1、HelloServer ：server类，启动Netty server 2、HelloServerInHandler：server的handler，接收客户端消息，并向客户端发送消息 3、HelloClient：client类，建立于Netty server的连接

4、HelloClientIntHandler：client的handler，接收server端的消息，并向服务端发送消息

一、先加入必要的类库：

二、HelloServer代码如下：

package com.yao.netty;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.SocketChannel;import io.netty.channel.socket.nio.NioServerSocketChannel;public class HelloServer {	public void start(int port) throws Exception {		EventLoopGroup bossGroup = new NioEventLoopGroup();		EventLoopGroup workerGroup = new NioEventLoopGroup();		try {			ServerBootstrap b = new ServerBootstrap();			b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)					.childHandler(new ChannelInitializer
    
     () {						@Override						public void initChannel(SocketChannel ch)								throws Exception {							// 注册handler							ch.pipeline().addLast(new HelloServerInHandler());						}					}).option(ChannelOption.SO_BACKLOG, 128)					.childOption(ChannelOption.SO_KEEPALIVE, true);			ChannelFuture f = b.bind(port).sync();			f.channel().closeFuture().sync();		} finally {			workerGroup.shutdownGracefully();			bossGroup.shutdownGracefully();		}	}	public static void main(String[] args) throws Exception {		HelloServer server = new HelloServer();		server.start(8000);	}}
    

三、 HelloServerInHandler代码如下：

package com.yao.netty;import io.netty.buffer.ByteBuf;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.ChannelInboundHandlerAdapter;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;// 该handler是InboundHandler类型public class HelloServerInHandler extends ChannelInboundHandlerAdapter {	private static Log logger = LogFactory.getLog(HelloServerInHandler.class);	@Override	public void channelRead(ChannelHandlerContext ctx, Object msg)			throws Exception {		logger.info("HelloServerInHandler.channelRead");		ByteBuf result = (ByteBuf) msg;		byte[] result1 = new byte[result.readableBytes()];		// msg中存储的是ByteBuf类型的数据，把数据读取到byte[]中		result.readBytes(result1);		String resultStr = new String(result1);		// 接收并打印客户端的信息		System.out.println("Client said:" + resultStr);		// 释放资源，这行很关键		result.release();		// 向客户端发送消息		String response = "I am ok!";		// 在当前场景下，发送的数据必须转换成ByteBuf数组		ByteBuf encoded = ctx.alloc().buffer(4 * response.length());		encoded.writeBytes(response.getBytes());		ctx.write(encoded);		ctx.flush();	}	@Override	public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {		ctx.flush();	}}

四、 HelloClient代码如下：

package com.yao.netty;import io.netty.bootstrap.Bootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.SocketChannel;import io.netty.channel.socket.nio.NioSocketChannel;public class HelloClient {	public void connect(String host, int port) throws Exception {		EventLoopGroup workerGroup = new NioEventLoopGroup();		try {			Bootstrap b = new Bootstrap();			b.group(workerGroup).channel(NioSocketChannel.class).option(ChannelOption.SO_KEEPALIVE, true)			.handler(new ChannelInitializer
    
     () {				@Override				public void initChannel(SocketChannel ch) throws Exception {					ch.pipeline().addLast(new HelloClientIntHandler());				}			});			// Start the client.			ChannelFuture f = b.connect(host, port).sync();			// Wait until the connection is closed.			f.channel().closeFuture().sync();		} finally {			workerGroup.shutdownGracefully();		}	}	public static void main(String[] args) throws Exception {		HelloClient client = new HelloClient();		client.connect("127.0.0.1", 8000);	}}
    

五、 HelloClientIntHandler代码如下：

package com.yao.netty;import io.netty.buffer.ByteBuf;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.ChannelInboundHandlerAdapter;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;public class HelloClientIntHandler extends ChannelInboundHandlerAdapter {	private static Log logger = LogFactory.getLog(HelloClientIntHandler.class);	// 接收server端的消息，并打印出来	@Override	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {		logger.info("HelloClientIntHandler.channelRead");		ByteBuf result = (ByteBuf) msg;		byte[] result1 = new byte[result.readableBytes()];		result.readBytes(result1);		System.out.println("Server said:" + new String(result1));		result.release();	}	// 连接成功后，向server发送消息	@Override	public void channelActive(ChannelHandlerContext ctx) throws Exception {		logger.info("HelloClientIntHandler.channelActive");		String msg = "Are you ok?";		ByteBuf encoded = ctx.alloc().buffer(4 * msg.length());		encoded.writeBytes(msg.getBytes());		ctx.write(encoded);		ctx.flush();	}}

六、还有log4j.xml文件：

总结： 通过上面简单的实例可以发现： 1、在没有任何encoder、decoder的情况下，Netty发送接收数据都是按照ByteBuf的形式，其它形式都是不合法的。 2、接收发送数据操作都是通过handler实现的，handler在netty中占据了非常重要的位置。 3、netty的handler是基于事件触发的，例如当client连接server成功后，client中的HelloClientIntHandler的channelActive方法会自动调用。