netty

高性能，异步，事件驱动库

Unix io模型

阻塞io
非阻塞io，netty主要就是基于epoll的多路复用技术。
io复用模型
信号驱动io模型
异步io

linux io多路复用的调用：select，pselect，poll，epoll

epoll改进

进程打开的socket 描述符（fd）不受限制
io效率不会随着fd增加而下降
使用mmap加速内核与用户空间的消息传递
api简单

各种io对比

io.png

为什么使用netty

java原生nio库难用，netty开发门槛低
功能强大，内置多种编解码功能
稳定，性能强
bug少

Example

echo服务器

<dependency>
  <groupId>io.netty</groupId>
  <artifactId>netty</artifactId>
  <version>3.10.6.Final</version>
</dependency>

EchoServer.java

package com.netty;

import java.net.InetSocketAddress;
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.frame.DelimiterBasedFrameDecoder;
import org.jboss.netty.handler.codec.frame.Delimiters;
import org.jboss.netty.handler.codec.string.StringDecoder;
import org.jboss.netty.handler.codec.string.StringEncoder;

public class EchoServer {
    
    public static void main(String[] args) {
        ServerBootstrap bootstrap = new ServerBootstrap(
                new NioServerSocketChannelFactory(
                        Executors.newCachedThreadPool(),
                        Executors.newCachedThreadPool()));

        bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
            public ChannelPipeline getPipeline() {
                ChannelPipeline pipeline = Channels.pipeline();
                pipeline.addLast("framer", new DelimiterBasedFrameDecoder(
                                          8192, Delimiters.lineDelimiter()));
                pipeline.addLast("decoder", new StringDecoder());
                pipeline.addLast("encoder", new StringEncoder());
                          
                pipeline.addLast("echo", new EchoServerHandler());
                return pipeline; 
            }
        });
        bootstrap.bind(new InetSocketAddress(8090));
    }
     
}

EchoServerHandler.java

package com.netty;

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.SimpleChannelUpstreamHandler;

public class EchoServerHandler extends SimpleChannelUpstreamHandler {
  
      @Override
      public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
          e.getChannel().write("connect success.");
      }
    
      @Override
      public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
          e.getChannel().write(e.getMessage());
      }
  
      @Override
      public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) {
          e.getCause().printStackTrace();
          e.getChannel().close();
      }
 }