Netty之BIO（同步阻塞IO）、PIO（伪异步阻塞IO）、NIO（异步非阻塞IO）、AIO（异步非阻塞IO）、Netty

学习书籍：Netty权威指南

多种IO方式的比较：

1、BIO（同步阻塞IO）

使用ServerSocket绑定IP地址和监听端口，客户端发起连接，通过三次握手建立连接，用socket来进行通信，通过输入输出流的方式来进行同步阻塞的通信

每次客户端发起连接请求，都会启动一个线程

线程数量：客户端并发访问数为1：1，由于线程是JAVA虚拟机中非常宝贵的资源，一旦线程数急剧增加，系统性能会急剧下降，导致线程栈溢出，创建新的线程失败，并最终导致宕机

所以在JDK1.4之前，人们想到了一种方法，即PIO方式

2、PIO（伪异步阻塞IO）

使用线程池来处理客户端的请求

客户端个数：线程池最大线程数=M：N，其中M远大于N

在read和write的时候，还是IO阻塞的，只是把每个线程交由线程池来控制管理

3、NIO（异步阻塞IO）

用NIO方式处理IO

使用多路复用器Selector来轮询每个通道Channel，当通道中有事件时就通知处理，不会阻塞

使用相当复杂

4、AIO（真正的异步非阻塞IO）

NIO2.0引入了新的异步通道的概念，不需要使用多路复用器（Selector）对注册通道进行轮询即可实现异步读写，从而简化了NIO编程模型

使用Netty框架进行编程步骤

1、构建事件处理池

2、使用引导程序关联事件处理池、通道、事件处理器

3、绑定端口服务

4、等待操作完成

5、关闭事件处理池

几种IO的功能和特性对比

按照书上的例子码了一遍：

服务端：

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 NettyServer {public void bind(int port) throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workGroup = new NioEventLoopGroup();try {ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 1024).childHandler(new ChildChannelHandler());// 绑定端口，同步等待成功ChannelFuture f = b.bind(port).sync();// 等待服务端监听端口关闭f.channel().closeFuture().sync();} catch (Exception e) {// TODO: handle exception} finally {// 优雅退出，释放线程池资源bossGroup.shutdownGracefully();workGroup.shutdownGracefully();}}private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new NettyServerHandle());}}public static void main(String[] args) throws Exception {int port = 8080;if (args != null && args.length > 0) {try {port = Integer.valueOf(args[0]);} catch (Exception e) {e.printStackTrace();}}new NettyServer().bind(port);}}

服务端处理器：

import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;public class NettyServerHandle extends ChannelHandlerAdapter {public void channelRead(ChannelHandlerContext ctx, Object msg)throws Exception {ByteBuf buf = (ByteBuf) msg;byte[] req = new byte[buf.readableBytes()];buf.readBytes(req);String body = new String(req, "UTF-8");System.out.println("The time server receive order:" + body);String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new java.util.Date(System.currentTimeMillis()).toString() : "BAD ORDER";ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());ctx.write(resp);}public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {ctx.flush();}public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {ctx.close();}}

客户端：

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 NettyClient {public void connect(int port, String host) throws Exception {// 1、创建线程池EventLoopGroup group = new NioEventLoopGroup();try {// 2、使用引导器关联线程池、通道、通达处理器、设置执行参数Bootstrap b = new Bootstrap();b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true).handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch)throws Exception {ch.pipeline().addLast(new NettyClientHandle());}});// 发起异步连接操作 3、绑定端口同步操作ChannelFuture f = b.connect(host, port).sync();// 4、监听端口关闭f.channel().closeFuture().sync();} catch (Exception e) {// TODO: handle exception} finally {// 优雅退出，释放NIO线程组 5、释放资源group.shutdownGracefully();}}public static void main(String[] args) throws Exception {int port = 8080;if (args != null && args.length > 0) {try {port = Integer.valueOf(args[0]);} catch (Exception e) {e.printStackTrace();}}new NettyClient().connect(port, "127.0.0.1");}}

客户端处理器：

import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import java.util.logging.Logger;public class NettyClientHandle extends ChannelHandlerAdapter {private static final Logger logger = Logger.getLogger(NettyClientHandle.class.getName());private final ByteBuf firstMessage;public NettyClientHandle() {byte[] req = "QUERY TIME ORDER".getBytes();firstMessage = Unpooled.buffer(req.length);firstMessage.writeBytes(req);}public void channelActive(ChannelHandlerContext ctx) {ctx.writeAndFlush(firstMessage);}public void channelRead(ChannelHandlerContext ctx, Object msg)throws Exception {ByteBuf buf = (ByteBuf) msg;byte[] req = new byte[buf.readableBytes()];buf.readBytes(req);String body = new String(req, "UTF-8");System.out.println("Now is:" + body);}public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {// 释放资源logger.warning("Unexpected exception from downstream:"+ cause.getMessage());ctx.close();}}