（一）BIO（Blocking I/O 阻塞I/O）

阻塞I/O的连接accept()方法及数据读取的read()方法都是阻塞的，也就是说没有客户端发起连接时会阻塞，客户端发起连接后不发送数据也会阻塞。

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;/**
* 阻塞IO
*/
public class BioServerDemo {public static void main(String[] args) throws IOException {ServerSocket serverSocket = new ServerSocket(9000);while(true){System.out.println("等待连接。。");//阻塞方法//可以通过控制台输入命令进行连接：telnet localhost 9000，CTRL+]进入Telnet指令Socket clientSocket = serverSocket.accept();System.out.println("有客户端连接了。。");//虽然采用多线程可以支持多个线程同时访问，但是会引发C10K问题//C10K->connection=1w，C10M->connection=1000w，就是连接数很多的意思//new Thread(new Runnable() {//	@Override//	public void run() {//		try {handler(clientSocket);//		} catch (IOException e) {//			e.printStackTrace();//		}//	}//}).start();}}private static void handler(Socket clientSocket) throws IOException {byte[] bytes = new byte[1024];System.out.println("准备read。。");//接收客户端的数据，阻塞方法，客户端没有发送数据，服务端就会没有数据可读时就阻塞int read  = clientSocket.getInputStream().read(bytes);System.out.println("read完毕。。");if (read !=-1){System.out.println("接收客户端的数据："+new String(bytes,0,read));}//clientSocket.getOutputStream().write("HelloClint".getBytes(StandardCharsets.UTF_8));//clientSocket.getOutputStream().flush();}
}

（二）NIO（Non-Blocking I/O 非阻塞I/O）

非阻塞I/O在客户端连接方法accept()和read()方法中都不会阻塞，我们可以通过返回值判断是否有客户端发起连接或者发送数据，进行相应的处理。
简单的NIO因为是通过遍历的方式，会有大量的空循环

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;/***初版- NIO（非阻塞）编程*/
public class NioServer {static List<SocketChannel> channelList = new ArrayList<>();public static void main(String[] args) throws IOException {ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();serverSocketChannel.socket().bind(new InetSocketAddress(9000));//这里可选非阻塞和阻塞，如果选择阻塞true，下面的accept()方法会阻塞线程serverSocketChannel.configureBlocking(false);System.out.println("服务启动成功");while (true){SocketChannel socketChannel = serverSocketChannel.accept();if(socketChannel!=null){System.out.println("连接成功");//这里可选非阻塞和阻塞，如果选择阻塞true，下面的read()方法会阻塞线程socketChannel.configureBlocking(false);//将所有连接channel交给一个集合进行管理channelList.add(socketChannel);}//问题点： 空循环时间耗时太久Iterator<SocketChannel> iterator = channelList.iterator();//遍历访问所有channel集合获取客户端发送的数据，如果有任何一个连接客户端发送了数据，那么就处理当前channel里的数据while (iterator.hasNext()){SocketChannel sc = iterator.next();ByteBuffer byteBuffer = ByteBuffer.allocate(128);int len = sc.read(byteBuffer);if (len>0){System.out.println("接收到消息："+new String(byteBuffer.array()));}else if(len ==-1){iterator.remove();System.out.println("客户端断开连接");}}}}
}

（三）IO多路复用–Selector

通过一个多路复用器selector对channel进行管理，这样

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
/***进阶版- NIO（非阻塞）编程* 这是netty和Redis的雏形*/
public class NioSelectorServer {public static void main(String[] args) throws IOException {ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();serverSocketChannel.socket().bind(new InetSocketAddress(9000));serverSocketChannel.configureBlocking(false);//启用epoll模型，这个对应epoll_create()方法Selector selector = Selector.open();//注册阻塞事件：创建连接，这个对应epoll模型的epoll_ctl()方法SelectionKey selectionKey = serverSocketChannel.register(selector,SelectionKey.OP_ACCEPT);System.out.println("服务启动成功");while (true){//阻塞等待需要处理的事件发生，包括连接事件和数据读取事件，如果没有客户端发起连接或者客户端发送数据，这里会一直阻塞。这个对应epoll模型的epoll_wait()方法selector.select();//获取阻塞的事件Set<SelectionKey> selectionKeys = selector.selectedKeys();//对阻塞事件进行遍历Iterator<SelectionKey> iterator = selectionKeys.iterator();if(iterator.hasNext()){SelectionKey key =iterator.next();if(key.isAcceptable()){//这里只针对连接事件，ServerSocketChannel server = (ServerSocketChannel) key.channel();SocketChannel socketChannel = server.accept();socketChannel.configureBlocking(false);//连接建立后，注册阻塞事件：读取数据SelectionKey selKey = socketChannel.register(selector,SelectionKey.OP_READ);}else if(key.isReadable()){//这里只针对read事件，有需要可以针对write事件处理SocketChannel socketChannel = (SocketChannel) key.channel();ByteBuffer byteBuffer = ByteBuffer.allocate(128);socketChannel.configureBlocking(false);int len  = socketChannel.read(byteBuffer);if(len >0 ){System.out.println("接收到消息："+new String(byteBuffer.array()));}else if(len ==-1 )//关闭socketsocketChannel.close();System.out.println("接收完成");}}//把处理完的阻塞事件移除iterator.remove();}}}
}

（四）Netty

Netty核心组件

• Bootstrap和ServerBootstrap：当需要连接客户端或者服务器绑定指定端口时需要使用Bootstrap，ServerBootstrap有两种类型，一种是用于客户端的Bootstrap，一种是用于服务端 的ServerBootstrap。
• Channel：相当于socket，与另一端进行通信的通道，具备bind、connect、read、write等IO操作的能力。
• EventLoop：事件循环，负责处理Channel的IO事件,一个EventLoopGroup包含多个EventLoop，一个EventLoop可被分配至多个Channel，一个Channel只能注册于一个EventLoop，一个EventLoop只能与一个Thread绑定。
• ChannelFuture：channel IO事件的异步操作结果。
• ChannelHandler：包含IO事件具体的业务逻辑。
• ChannelPipeline：ChannelHandler的管道容器。

DEMO
Netty服务端

public class NettyServer {public static void main(String[] args) throws InterruptedException {EventLoopGroup parentGroup = new NioEventLoopGroup();EventLoopGroup childGroup = new NioEventLoopGroup();try {//2.创建服务端启动引导/辅助类：ServerBootstrapServerBootstrap bootstrap = new ServerBootstrap();//3.给引导类配置两大线程组,确定了线程模型bootstrap.group(parentGroup, childGroup)// (非必备)打印日志.handler(new LoggingHandler(LogLevel.INFO))// 4.指定 IO 模型.channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ChannelPipeline pipeline = ch.pipeline();pipeline.addLast(new StringDecoder());pipeline.addLast(new StringEncoder());/***  服务端添加IdleStateHandler心跳检测处理器,添加自定义处理Handler类实现userEventTriggered()方法作为超时事件的逻辑处理.*  IdleStateHandler心跳检测每十五秒进行一次读检测，如果十五秒内ChannelRead()方法未被调用则触发一次userEventTrigger()方法*  服务端为读IDLE*  pipeline.AddLast(new IdleStateHandler(15, 0, 0));//第一个参数为读，第二个为写，第三个为读写全部*/pipeline.addLast(new IdleStateHandler(15, 0, 0, TimeUnit.SECONDS));//5.可以自定义客户端消息的业务处理逻辑pipeline.addLast(new DemoSocketServerHandler());}});//            ChannelFuture future = bootstrap.bind(8888).sync().addListener(new ChannelFutureListener() {
//                @Override
//                public void operationComplete(ChannelFuture channelFuture) throws Exception {
//                    System.out.println("监听端口已经启动");
//                }
//            });ChannelFuture future = bootstrap.bind(8888).sync().addListener( future1 -> {if (future1.isSuccess()){System.out.println("监听端口已经启动!");} else {System.out.println("监听端口还未启动!");}} );System.out.println("服务器已启动。。。");future.channel().closeFuture().sync();} finally {parentGroup.shutdownGracefully();childGroup.shutdownGracefully();}}
}

Netty客户端

public class NettyClient {public static void main(String[] args) throws InterruptedException {NioEventLoopGroup eventLoopGroup = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ChannelPipeline pipeline = ch.pipeline();pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));pipeline.addLast(new DemoSocketClientHandler());}});ChannelFuture future = bootstrap.connect("localhost", 8888).sync();future.channel().closeFuture().sync();} finally {if(eventLoopGroup != null) {eventLoopGroup.shutdownGracefully();}}}
}

服务端处理handler

public class DemoSocketServerHandler extends ChannelInboundHandlerAdapter {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {InetSocketAddress inetSocketAddress = (InetSocketAddress) ctx.channel().remoteAddress();String ip = inetSocketAddress.getAddress().getHostAddress();int port = inetSocketAddress.getPort();super.channelActive(ctx);System.out.println(ip+":"+port+" 上线了");}@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {System.out.println(msg);System.out.println("Client Address ====== " + ctx.channel().remoteAddress());ctx.channel().writeAndFlush("from server:" + UUID.randomUUID());ctx.fireChannelActive();TimeUnit.MILLISECONDS.sleep(500);}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}@Overridepublic void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {if (evt instanceof IdleStateEvent) {IdleStateEvent idleStateEvent = (IdleStateEvent) evt;if (idleStateEvent.state() == IdleState.READER_IDLE) {InetSocketAddress inetSocketAddress = (InetSocketAddress) ctx.channel().remoteAddress();String ip = inetSocketAddress.getAddress().getHostAddress();System.out.println((ip + ":" + inetSocketAddress.getPort() + "close"));ctx.channel().close();}}}
}

客户端处理handler

public class DemoSocketClientHandler extends ChannelInboundHandlerAdapter {@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg)throws Exception {System.out.println(msg);ctx.channel().writeAndFlush("from client: " + System.currentTimeMillis());TimeUnit.MILLISECONDS.sleep(5000);}@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {ctx.channel().writeAndFlush("from client：begin talking");}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}//超时则关闭链路@Overridepublic void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {if (evt instanceof IdleStateEvent) {IdleStateEvent idleStateEvent = (IdleStateEvent) evt;if (idleStateEvent.state() == IdleState.READER_IDLE) {InetSocketAddress inetSocketAddress = (InetSocketAddress) ctx.channel().remoteAddress();String ip = inetSocketAddress.getAddress().getHostAddress();System.out.println((ip + ":" + inetSocketAddress.getPort() + "close"));ctx.channel().close();}}}
}