netty 学习 （1）

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>() {
						@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<SocketChannel>() {
				@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：

<?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。