《Netty源码学习一：pipleLine、FrameDecoder、Reactor多线程模型思想》

本文链接：https://blog.youkuaiyun.com/weixin_41262453/article/details/89034474

本文详细介绍了Netty的入门代码示例，着重解析了消息如何在Pipeline中流转，FrameDecoder的解码过程，以及Netty的Reactor多线程模型思想。通过Server和Client的交互，展示了ChannelHandler的生命周期方法，并讨论了ChannelPipeline的Upstream和Downstream机制。最后，深入讲解了FrameDecoder的工作原理，以及从NIO的Reactor模型理解Netty的Reactor实现。

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《Netty源码学习一： pipleLine、FrameDecoder、Reactor多线程模型思想》

Netty入门代码例子
Netty中的消息如何在管道pipeline中流转
如何理解Netty的编解码器FrameDecoder
从NIO Reactor多线程模型理解Netty Reactor模型

Netty入门代码例子

服务端：Server

import java.net.InetSocketAddress;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.jboss.netty.bootstrap.ServerBootstrap;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.socket.nio.NioServerSocketChannelFactory;
import org.jboss.netty.handler.codec.string.StringDecoder;
import org.jboss.netty.handler.codec.string.StringEncoder;
public class Server {
   
   
	public static void main(String[] args) {
   
   
		//服务类
		ServerBootstrap bootstrap = new ServerBootstrap();		
		//boss线程监听端口，worker线程负责数据读写
		ExecutorService boss = Executors.newCachedThreadPool();
		ExecutorService worker = Executors.newCachedThreadPool();		
		//设置niosocket工厂
		bootstrap.setFactory(new NioServerSocketChannelFactory(boss, worker));		
		//设置管道的工厂
		bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
   
   		
			@Override
			public ChannelPipeline getPipeline() throws Exception {
   
   
				ChannelPipeline pipeline = Channels.pipeline();
				pipeline.addLast("decoder", new StringDecoder());
				pipeline.addLast("encoder", new StringEncoder());
				pipeline.addLast("helloHandler", new HelloHandler());
				return pipeline;
			}
		});		
		bootstrap.bind(new InetSocketAddress(10101));		
		System.out.println("start!!!");		
	}
}

HelloHandler 继承了SimpleChannelHandler，SimpleChannelHandler用于处理消息接收和写的handler类的父类。为了messageReceived、exceptionCaught、channelConnected、channelDisconnected、channelClosed方法能运行效果更加明显，增加输出语句。

import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelStateEvent;
import org.jboss.netty.channel.ExceptionEvent;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.channel.SimpleChannelHandler;
public class HelloHandler extends SimpleChannelHandler {
   
   
	/**
	 * 接收消息
	 */
	@Override
	public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
   
   
	//由于服务端管道增加了编码解码器，所以接收后的数据处理起来可以直接转换
		String s = (String) e.getMessage();
		System.out.println(s);		
		//回写数据
		ctx.getChannel().write("hi");
		super.messageReceived(ctx, e);
	}
	/**
	 * messageReceived执行出异常，会执行该方法 捕获异常
	 */
	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception {
   
   
		System.out.println("exceptionCaught");
		super.exceptionCaught(ctx, e);
	}
	/**
	 * 新连接
	 */
	@Override
	public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
   
   
		System.out.println("channelConnected");
		super.channelConnected(ctx, e);
	}
	/**
	 * 必须是链接已经建立，关闭通道的时候才会触发
	 */
	@Override
	public void channelDisconnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
   
   
		System.out.println("channelDisconnected");
		super.channelDisconnected(ctx, e);
	}
	/**
	 * channel关闭的时候触发
	 */
	@Override
	public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
   
   
		System.out.println("channelClosed");
		super.channelClosed(ctx, e);
	}
}

客户端：

import java.net.InetSocketAddress;
import java.util.Scanner;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.jboss.netty.bootstrap.ClientBootstrap;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelFuture;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.socket.nio.NioClientSocketChannelFactory;
import org.jboss.netty.handler.codec.string.StringDecoder;
import org.jboss.netty.handler.codec.string.StringEncoder;
public class Client {
   
   
	public static void main(String[] args) {
   
   		
		//服务类
		ClientBootstrap bootstrap = new  ClientBootstrap();		
		//线程池
		ExecutorService boss = Executors.newCachedThreadPool();
		ExecutorService worker = Executors.newCachedThreadPool();		
		//socket工厂
		bootstrap.setFactory(new NioClientSocketChannelFactory(boss, worker));		
		//管道工厂
		bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
   
   			
			@Override
			public ChannelPipeline getPipeline() throws Exception {
   
   
				ChannelPipeline pipeline = Channels.pipeline();
				pipeline.addLast("decoder", new StringDecoder());
				pipeline.addLast("encoder", new StringEncoder());
				pipeline.addLast("hiHandler", new HiHandler());
				return pipeline;
			}
		});		
		//连接服务端
		ChannelFuture connect = bootstrap.connect(new InetSocketAddress("127.0.0.1", 10101));
		Channel channel = connect.getChannel();		
		System.out.