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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<SocketChannel>() {@Overridepublic void initChannel(SocketChannel ch)throws Exception {// 注册handlerch.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);@Overridepublic 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();}@Overridepublic 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<SocketChannel>() {@Overridepublic 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@Overridepublic 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@Overridepublic 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：

<?xml version="1.0"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"><log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"><appender name="CONSOLE" class="org.apache.log4j.ConsoleAppender"><layout class="org.apache.log4j.PatternLayout"><param name="ConversionPattern" value="[%-5p] [%d] [%t] [%c] %m%n"/></layout></appender><appender name="FILE" class="org.apache.log4j.DailyRollingFileAppender"><param name="File" value="./log/netty.log"/><layout class="org.apache.log4j.PatternLayout"><param name="ConversionPattern" value="[%-5p] [%d] [%t] [%c] %m%n"/></layout></appender><appender name="FILE_ERR" class="org.apache.log4j.DailyRollingFileAppender"><param name="File" value="./log/netty_err.log"/><param name="Threshold" value="ERROR" /><layout class="org.apache.log4j.PatternLayout"><param name="ConversionPattern" value="[%-5p] [%d] [%t] [%c] %m%n"/></layout></appender>	    <logger name="io.netty" additivity="false"><level value="INFO,DEBUG" /><appender-ref ref="FILE" /><appender-ref ref="FILE_ERR" /><appender-ref ref="CONSOLE" /></logger><logger name="com.yao" additivity="false"><level value="INFO,DEBUG" /><appender-ref ref="FILE" /><appender-ref ref="FILE_ERR" /><appender-ref ref="CONSOLE" /></logger><root><level value="debug"/><appender-ref ref="FILE"/><appender-ref ref="CONSOLE"/><appender-ref ref="FILE_ERR" /></root></log4j:configuration>

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。