Netty权威指南读书笔记-第三章

首先回顾一下用NIO开发TimeServer的步骤：

1.创建ServerSocketChannel，配置为非阻塞模式；

2.绑定监听，配置TCP参数，比如backlog大小；

3.创建一个独立的IO线程，用于轮询多路复用器Selector；

4.创建Selector，将之前创建的ServerSocketChannel注册到Selector上，监听SelectionKey.OP_ACCEPT；

5.启动IO线程，在循环体中执行Selector.select()方法，轮询就绪的Channel；

6.当轮询到了处于就绪状态的Channel时，需要对其进行判断，如果是OP_ACCEPT状态，说明是新的客户端接入，则调用ServerSocketChannel.accept()方法接受新的客户端；

7.设置新接入的客户端链路SocketChannel为非阻塞模式，配置其他的一些TCP参数；

8.将SocketChannel注册到Selector，监听OP_READ操作位；

9.如果轮询的Channel为OP_READ，则说明SocketChannel有新的数据包可读取，则构造ByteBuffer对象读取；

10.如果轮询的Channel为OP_WRITE,则说明还有数据没有发送完成，需要继续发送。

一个简单的NIO服务器端程序如果用JDK的NIO类库进行开发，则需要以上的10多个步骤才能完成消息的发送和读取，这也是我们为什么选择用Netty或者其他NIO框架进行开发的原因。

下面用Netty实现时间服务器

1.服务器端代码

package com.yy.test.netty;


import java.util.Date;

import org.apache.log4j.Logger;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
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 TimeServer {
	static Logger logger = Logger.getLogger(TimeServer.class);
	
	public void bind(int port) throws Exception{
		//配置NIO服务器端线程组
		EventLoopGroup bossGroup = new NioEventLoopGroup();
		EventLoopGroup workerGroup = new NioEventLoopGroup();
		try{
		ServerBootstrap server = new ServerBootstrap();
		server.group(bossGroup, workerGroup)
		.channel(NioServerSocketChannel.class)
		.option(ChannelOption.SO_BACKLOG, 1024)
		.childHandler(new childHandler());
		
		//绑定端口。同步等待		
		ChannelFuture channelFuture = server.bind(port).sync();
		//等待服务器端监听端口关闭
		channelFuture.channel().closeFuture().sync();
		}finally{
			bossGroup.shutdownGracefully();//优雅的退出，释放NIO线程组
			workerGroup.shutdownGracefully();
		}
	}

	public static void main(String[] args) {
		try {
			new TimeServer().bind(8085);
		} catch (Exception e) {
			logger.error("TimeServer.main error:",e);
		}
	}
	
	
}
class childHandler extends ChannelInitializer{

	@Override
	protected void initChannel(SocketChannel ch) throws Exception {
		ch.pipeline().addLast(new TimeServerHandler());
	}

	
}

class TimeServerHandler extends ChannelHandlerAdapter{
	static Logger logger = Logger.getLogger(TimeServerHandler.class);
	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
		ByteBuf buf = (ByteBuf) msg;
		byte[] bytes = new byte[buf.readableBytes()];
		buf.readBytes(bytes);
		String content = new String(bytes,"utf-8");
		System.out.println("The server received "+content);
		String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(content) ? new Date(System.currentTimeMillis()).toString():"BAD QUERY";
		ByteBuf writeBuf = Unpooled.copiedBuffer(currentTime.getBytes());
		ctx.write(writeBuf);
	}
	
	@Override
	public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
		ctx.flush();
	}
	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		ctx.close();
	}
}

2.客户端代码

package com.yy.test.netty;

import java.net.InetSocketAddress;

import org.apache.log4j.Logger;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

public class TimeClient {
	static Logger logger = Logger.getLogger(TimeClient.class);
	
	public void connect(String host,int port) throws Exception{
		//配置NIO客户端线程组
		NioEventLoopGroup group = new NioEventLoopGroup();
		try{
		Bootstrap client = new Bootstrap();
		client.group(group)
		.option(ChannelOption.TCP_NODELAY, true)
		.channel(NioSocketChannel.class)
		.handler(new ChannelInitializer() {

			@Override
			protected void initChannel(SocketChannel ch) throws Exception {
				ch.pipeline().addLast(new TimeClientHandler());
			}
		});
		//发起异步连接请求	
		ChannelFuture channelFuture = client.connect(new InetSocketAddress(host, port)).sync();
		//等待客户端链路关闭
		channelFuture.channel().closeFuture().sync();
		}finally{
			group.shutdownGracefully();//优雅的退出，释放NIO线程组
		}
	}
	public static void main(String[] args) {
		try {
			new TimeClient().connect("127.0.0.1", 8085);
		} catch (Exception e) {
			logger.error("TimeClient.main error:",e);
		}
	}

}
class TimeClientHandler extends ChannelHandlerAdapter{
	static Logger logger = Logger.getLogger(TimeClientHandler.class);
	private ByteBuf buffer;
	public TimeClientHandler(){
		
		byte[] bytes = "QUERY TIME ORDER".getBytes();
		buffer = Unpooled.buffer(bytes.length);
		buffer.writeBytes(bytes);
	}
	
	@Override
	public void channelActive(ChannelHandlerContext ctx) throws Exception {
		ctx.writeAndFlush(buffer);
	}
	
	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
		ByteBuf buf = (ByteBuf)msg;
		byte[] bytes = new byte[buf.readableBytes()];
		buf.readBytes(bytes);
		String body = new String(bytes,"utf-8");
		logger.info("Now is "+body);
	}
	
	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		logger.error("TimeClientHandler.error:",cause);
		ctx.close();
	}
}

3.运行结果

通过用Netty重构时间服务器程序，可以发现相比于传统的NIO程序，Netty的代码更加简洁、开发难度更低、拓展度也更好，非常适合作为基础通信框架被用户集成和使用。