目标客户端和服务端互相通信本文主要是实战练习照着敲然后debug看为什么就行前置理解模型核心类特点简述BIOServerSocket / Socket一个连接一个线程accept()和read()都会阻塞简单但连接多了线程爆炸NIOSelector / ServerSocketChannel / SocketChannel / ByteBuffer一个 Selector 管理多个 Channel非阻塞轮询复杂但一个线程扛几百连接NettyServerBootstrap / EventLoopGroup / Pipeline / Handler封装了 NIO 的复杂性用责任链处理数据高性能框架写业务逻辑就行练习递进关系BIO 理解通信本质 → NIO 理解多路复用 → Netty 理解工程化封装。三种服务端可以混搭客户端底层都是 TCP 协议BIO 客户端可以连 NIO 服务端反之亦然。IO服务端publicclassIOServer{privatestaticfinalThreadPoolExecutorclientPoolnewThreadPoolExecutor(2,//最小线程数3,//最大线程数60L,//线程空闲时间TimeUnit.SECONDS,// 时间单位newArrayBlockingQueue(1),// 任务队列容量newThreadPoolExecutor.CallerRunsPolicy()// 拒绝策略);publicstaticvoidmain(String[]args)throwsIOException{//IO服务端ServerSocketserverSocketnewServerSocket(8888);while(true){// 添加线程池状态监控System.out.println(当前线程池状态 - 活跃线程: clientPool.getActiveCount(), 队列大小: clientPool.getQueue().size());SocketclientSocketserverSocket.accept();System.out.println(客户端连接: clientSocket.getInetAddress());// new Thread(()-handleClient(clientSocket)).start();try{// 提交任务clientPool.execute(()-handleClient(clientSocket));System.out.println(✅ 任务已提交);}catch(Exceptione){System.err.println(❌ 提交失败);clientSocket.close();}}}privatestaticvoidhandleClient(SocketclientSocket){try{clientSocket.setSoTimeout(60000);}catch(SocketExceptione){return;}//inpustStream获取输入流//outputStream获取输出流//InputStreamReader将输入流转换为字符流//BufferedReader将字符流转换为缓冲流try(InputStreaminputStreamclientSocket.getInputStream();BufferedReaderreadernewBufferedReader(newInputStreamReader(inputStream));){Stringline;while((linereader.readLine())!null){System.out.printf(Thread.currentThread().getName()收到客户端消息:line\n);}System.out.println(客户端已断开);}catch(SocketTimeoutExceptione){System.out.println(客户端空闲超时主动踢下线);}catch(IOExceptione){e.printStackTrace();}finally{try{clientSocket.close();// 只关客户端不关服务端System.out.println(资源已清理线程退出);}catch(IOExceptione){e.printStackTrace();}}}}客户端publicclassIOClient{publicstaticvoidmain(String[]args)throwsIOException{//IO客户端SocketsocketnewSocket(127.0.0.1,8888);OutputStreamossocket.getOutputStream();ScannerscnewScanner(System.in);while(sc.hasNext()){Stringmsgsc.nextLine();if(exit.equalsIgnoreCase(msg)){socket.shutdownOutput();// 关闭输出流通知服务端读完了break;}os.write((msg\n).getBytes());os.flush();}os.close();socket.close();}}NIO服务端publicclassNIOServer{publicstaticfinalThreadPoolExecutortpnewThreadPoolExecutor(2,10,60L,TimeUnit.SECONDS,newArrayBlockingQueue(1),newThreadPoolExecutor.CallerRunsPolicy());privateNIOServerstart()throwsIOException{//配置nio管理员SelectorselectorSelector.open();ServerSocketChannelserverSocketChannelServerSocketChannel.open();serverSocketChannel.bind(newInetSocketAddress(8888));serverSocketChannel.configureBlocking(false);//取消阻塞// 注册serverSocketChannel.register(selector,SelectionKey.OP_ACCEPT);while(true){selector.select();SetSelectionKeyselectionKeysselector.selectedKeys();//获取迭代器IteratorSelectionKeyiteratorselectionKeys.iterator();while(iterator.hasNext()){SelectionKeykeyiterator.next();iterator.remove();// 处理不同事件if(key.isAcceptable()){handleAccept(key);// 新客户端连接}elseif(key.isReadable()){handleRead(key);// 客户端发消息}}}}publicstaticvoidmain(String[]args)throwsIOException{newNIOServer().start();}privatestaticvoidhandleAccept(SelectionKeykey)throwsIOException{ServerSocketChannelserver(ServerSocketChannel)key.channel();SocketChannelchannelserver.accept();channel.configureBlocking(false);channel.register(key.selector(),SelectionKey.OP_READ,ByteBuffer.allocate(1024));System.out.println(\n新客户端连接channel.getRemoteAddress());}privatestaticvoidhandleRead(SelectionKeykey){SocketChannelclient(SocketChannel)key.channel();ByteBufferbuffer(ByteBuffer)key.attachment();try{intlenclient.read(buffer);// 非阻塞读取if(len-1){// 客户端断开System.out.println(客户端断开client.getRemoteAddress());client.close();key.cancel();return;}// 切换读模式buffer.flip();StringmsgnewString(buffer.array(),0,len);buffer.clear();System.out.println(收到消息msg);tp.execute(()-{System.out.println(Thread.currentThread().getName() 执行业务 → msg);});}catch(IOExceptione){// 强制断开try{client.close();key.cancel();}catch(IOExceptionex){ex.printStackTrace();}}}}客户端publicclassNIOClient{publicstaticvoidmain(String[]args)throwsIOException{// 1. 打开客户端通道SocketChannelclientSocketChannel.open(newInetSocketAddress(127.0.0.1,8888));client.configureBlocking(false);// 非阻塞模式ScannerscnewScanner(System.in);ByteBufferbufferByteBuffer.allocate(1024);while(sc.hasNext()){Stringmsgsc.nextLine();if(exit.equalsIgnoreCase(msg)){break;}// 写数据到服务端buffer.clear();buffer.put((msg\n).getBytes());buffer.flip();client.write(buffer);}client.close();}}Netty客户端public class NettyClient { private Channel channel; public final EventLoopGroup group new NioEventLoopGroup(); public static void main(String[] args) throws InterruptedException { NettyClient client new NettyClient(); new Thread(()-{ try { client.start(127.0.0.1,8888); } catch (InterruptedException e) { throw new RuntimeException(e); } }).start(); Scanner sc new Scanner(System.in); while (sc.hasNext()){ String msg sc.nextLine(); if(exit.equalsIgnoreCase(msg)) { client.sendMsg(拜拜); client.close(); break; } client.sendMsg(msg); } } public void start(String host,Integer port) throws InterruptedException { Bootstrap bootstrap new Bootstrap(); bootstrap .group(group) .channel(NioSocketChannel.class) .handler(new ChannelInitializerSocketChannel() { Override protected void initChannel(SocketChannel ch) throws Exception { ch.pipeline() // .addLast(new LoggingHandler(LogLevel.INFO)) // 拆包参数和服务端一模一样 .addLast(new LengthFieldBasedFrameDecoder(1024 * 1024, 0, 4, 0, 4)) .addLast(new LengthFieldPrepender(4)) .addLast(new StringDecoder()) .addLast(new StringEncoder()) // 客户端心跳 .addLast(new IdleStateHandler(30, 60, 120)) // 客户端自定义业务处理器 .addLast(new MyClientHandler()); } }); ChannelFuture future bootstrap.connect(host, port).sync(); this.channel future.channel(); future.channel().closeFuture().sync(); } public void sendMsg(String msg) { if (channel ! null channel.isActive()) { channel.writeAndFlush(msg); } else { System.out.println(连接未成功无法发送); } } public void close() { if (channel ! null) channel.close(); group.shutdownGracefully(); } }方法配置public class MyClientHandler extends SimpleChannelInboundHandlerString { Override protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception { System.out.println(客户端收到服务端消息 msg); } // 连接成功建立 Override public void channelActive(ChannelHandlerContext ctx) { System.out.println(客户端成功连接服务端); // 连接成功主动发一条消息 ctx.writeAndFlush(客户端上线啦); } // 连接断开 Override public void channelInactive(ChannelHandlerContext ctx) { System.out.println(客户端与服务端连接断开); } // 心跳事件处理 Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) { // 判断是不是空闲事件 if (evt instanceof IdleStateEvent) { IdleStateEvent event (IdleStateEvent) evt; // 如果是【写空闲】 30秒没发消息 if (event.state() IdleState.WRITER_IDLE) { // 自动发一个心跳包 ctx.writeAndFlush(heartbeat); } } } }服务端public class NettyServer { private static final EventLoopGroup boss new NioEventLoopGroup(1); private static final EventLoopGroup worker new NioEventLoopGroup(); public void start(int port) throws InterruptedException { try { ServerBootstrap bootstrap new ServerBootstrap(); bootstrap .group(boss, worker) .channel(NioServerSocketChannel.class) .childHandler(new ChannelInitializerSocketChannel() { Override protected void initChannel(SocketChannel ch) throws Exception { //输入输出 ChannelPipeline pipeline ch.pipeline(); // pipeline.addLast(new LoggingHandler(LogLevel.INFO)); //日志打印 pipeline.addLast(new LengthFieldBasedFrameDecoder(1024 * 1024, 0, 4, 0, 4)); pipeline.addLast(new LengthFieldPrepender(4)); pipeline.addLast(new StringDecoder()); pipeline.addLast(new StringEncoder()); pipeline.addLast(new IdleStateHandler(60, 30, 120)); pipeline.addLast(new MyServerHandler()); } }); //绑定端口 同步阻塞 ChannelFuture channelFuture bootstrap.bind(port).sync(); //等待服务关闭通道 channelFuture.channel().closeFuture().sync(); }catch(Exception e){ e.printStackTrace(); }finally { boss.shutdownGracefully(); worker.shutdownGracefully(); } } public static void main(String[] args) throws InterruptedException { // 启动服务端 new NettyServer().start(8888); } }方法配置public class MyServerHandler extends SimpleChannelInboundHandlerString { //全局用户集合concurrentHashMap public static final SetString ONLINE_CLIENTS ConcurrentHashMap.newKeySet(); private static final ThreadPoolExecutor tp new ThreadPoolExecutor(5, 10, 60L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue(1),new ThreadPoolExecutor.AbortPolicy()); Override public void channelActive(ChannelHandlerContext ctx) { SocketAddress socketAddress ctx.channel().remoteAddress(); tp.execute(() - { ONLINE_CLIENTS.add(socketAddress.toString()); System.out.println(有新客户端连接 ctx.channel().remoteAddress()); System.out.println(当前人数ONLINE_CLIENTS.size()); ctx.writeAndFlush(欢迎连接); ctx.writeAndFlush(当前人数ONLINE_CLIENTS.size()); }); } Override public void channelReadComplete(ChannelHandlerContext ctx) { ctx.flush(); } Override public void channelInactive(ChannelHandlerContext ctx) { String clientAddr ctx.channel().remoteAddress().toString(); tp.execute(() - { System.out.println(客户端断开 clientAddr); ONLINE_CLIENTS.remove(clientAddr); System.out.println(当前在线人数 ONLINE_CLIENTS.size()); }); } Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { System.err.println(异常 cause.getMessage()); ctx.close(); } Override protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception { String name ctx.channel().remoteAddress().toString(); tp.execute(() - { try { System.out.println(name 发来一条消息 msg); ctx.writeAndFlush(ACK_OK); } catch (Exception e) { e.printStackTrace(); } }); } }