摘要：前言上文【从入门到放弃-SpringBoot】SpringBoot源码分析-请求过程中我们了解到，tomcat接收、返回请求的过程都是基于NIO实现的。日常工作中有很多基于NIO的使用，我们知道NI前

前言上文【从入门到放弃-SpringBoot】SpringBoot源码分析-请求过程中我们了解到，tomcat接收、返回请求的过程都是基于NIO实现的。日常工作中有很多基于NIO的使用，我们知道NI

前言

上文【从入门到放弃-SpringBoot】SpringBoot源码分析-请求过程中我们了解到，tomcat接收、返回请求的过程都是基于NIO实现的。日常工作中有很多基于NIO的使用，我们知道NIO可以提高系统的并发度，接下来的系列我们来深入学习下NIO，本文先从使用上简单概述。

NIO概述

NIO即non-blocking（New IO），是指jdk1.4 及以上版本里提供的新api。

NIO和IO最大的区别：IO是以流的方式处理数据，而NIO是以块的方式处理数据；IO对事件的处理是阻塞的，NIO是非阻塞的

NIO的核心部分：

• Channel
• Buffer
• Selector

NIO主要分为标准输入输出和网络请求

标准输入输出NIO

读取

private static void readNio() {    try {        //1、开启文件读取流        FileInputStream fileInputStream = new FileInputStream("/Users/my/Desktop/123.txt");        //2、获取fileChannel        FileChannel channel = fileInputStream.getChannel();        //3、设置ByteBuffer大小，一次能容纳capacity字节        int capacity = 9;        ByteBuffer bf = ByteBuffer.allocate(capacity);        //4、当read返回-1时，表示文件读取完毕        int length = -1;        while ((length = channel.read(bf)) != -1) {            byte[] bytes = bf.array();            System.out.println(new String(bytes, 0, length));            //4、将bf position置为0，方便下次读取            bf.clear();        }        channel.close();        fileInputStream.close();    } catch (IOException e) {        e.printStackTrace();    }}

写入

private static void writeNio() {    try {        //1、打开文件写入流        FileOutputStream fileOutputStream = new FileOutputStream("/Users/my/Desktop/123.txt");        //2、获取fileChannel        FileChannel channel = fileOutputStream.getChannel();        //3、初始化byteBuffer        String str = "萨达案发生大大sdada34;sdds'";        ByteBuffer bf = ByteBuffer.allocate(1024);        //4、将bf position置为0，方便下次读取        bf.clear();        //5、从byteBuffer的position位置填充byte        bf.put(str.getBytes());        //6、将bf position置为0，limit设置为position避免写入内容过多        bf.flip();        int length = 0;        //7、如果position小于limit即未写入完毕        while (bf.hasRemaining()) {            //8、将buffer内容写入channel            length = channel.write(bf);            System.out.println(bf);        }        channel.close();        fileOutputStream.close();    } catch (IOException e) {        e.printStackTrace();    }}

网络NIO

服务端

package com.my.tools.nio;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;public class ServerSocket {    private static ServerSocket serverSocket;    private Selector selector;    public static void main(String[] args) throws Exception {        ServerSocket.getInstance().init(8001).listen();    }    public static ServerSocket getInstance() {        if (serverSocket == null) {            synchronized (ServerSocket.class) {                if (serverSocket == null) {                    serverSocket = new ServerSocket();                }            }        }        return serverSocket;    }    public ServerSocket init(int port) throws IOException {        //初始化channel        ServerSocketChannel server = ServerSocketChannel.open();        //绑定本机8001端口        server.socket().bind(new InetSocketAddress(8001));        //设置为非阻塞模式        server.configureBlocking(false);        //开启selector管理器        selector = Selector.open();        //将selector注册至server，并设置只处理accept事件        server.register(selector, SelectionKey.OP_ACCEPT);        return this;    }    public void listen() throws Exception {        System.out.println("server start");        //无限循环持续监听        while (true) {            //会阻塞 直到监听到注册的事件            selector.select();            //获取唤醒的事件            Iterator<SelectionKey> selectorKeys = selector.selectedKeys().iterator();            while (selectorKeys.hasNext()) {                SelectionKey key = selectorKeys.next();                //将已取出的SelectionKey删除，防止重复处理                selectorKeys.remove();                if (key.isAcceptable()) {                    //获取到服务端的socket                    ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();                    //获取接收到的客户端socket                    SocketChannel socketChannel = serverSocketChannel.accept();                    socketChannel.configureBlocking(false);                    //向客户端写消息                    socketChannel.write(ByteBuffer.wrap(new String("hello, this is server").getBytes()));                    //注册监听read事件                    socketChannel.register(selector, SelectionKey.OP_READ);                    System.out.println("accept");                } else if (key.isReadable()) {                    //使用selector获取channel                    SocketChannel socketChannel = (SocketChannel) key.channel();                    socketChannel.configureBlocking(false);                    ByteBuffer buffer = ByteBuffer.allocate(1024);                    //读消息                    int length = socketChannel.read(buffer);                    String string = new String(buffer.array(), 0 , length);                    System.out.println("read:" + socketChannel + string);                    //写消息                    socketChannel.write(ByteBuffer.wrap(("server " + System.currentTimeMillis()).getBytes()));                    Thread.sleep(10000);                }            }        }    }}

客户端

package com.my.tools.nio;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.SocketChannel;import java.util.Iterator;public class ClientSocket {    public static ClientSocket clientSocket;    private static Selector selector;    public static void main(String[] args) throws Exception {        ClientSocket.getInstance().init("localhost", 8001).listen();    }    public static ClientSocket getInstance() {        if (clientSocket == null) {            synchronized (ClientSocket.class) {                if (clientSocket == null) {                    clientSocket = new ClientSocket();                }            }        }        return clientSocket;    }    public ClientSocket init(String ip, int port) throws IOException {        SocketChannel socketChannel = SocketChannel.open();        socketChannel.connect(new InetSocketAddress(ip, port));        socketChannel.configureBlocking(false);        selector = Selector.open();        socketChannel.register(selector, SelectionKey.OP_CONNECT | SelectionKey.OP_READ);        return this;    }    public void listen() throws Exception {        System.out.println("client start");        while (true) {            selector.select();            Iterator<SelectionKey> selectionKeys = selector.selectedKeys().iterator();            while (selectionKeys.hasNext()) {                SelectionKey selectionKey = selectionKeys.next();                selectionKeys.remove();                if (selectionKey.isConnectable()) {                    SocketChannel socketChannel = (SocketChannel) selectionKey.channel();                    socketChannel.configureBlocking(false);                    ByteBuffer buffer = ByteBuffer.wrap(new String("hello, this is client").getBytes());                    socketChannel.write(buffer);                    socketChannel.register(selector, SelectionKey.OP_READ);                    System.out.println("client write");                } else if (selectionKey.isReadable()) {                    SocketChannel socketChannel = (SocketChannel) selectionKey.channel();                    socketChannel.configureBlocking(false);                    ByteBuffer buffer = ByteBuffer.allocate(1024);                    int length = socketChannel.read(buffer);                    System.out.println("client read: " + socketChannel + new String(buffer.array(), 0, length));                    socketChannel.write(ByteBuffer.wrap(("client " + System.currentTimeMillis()).getBytes()));                    Thread.sleep(10000);                }            }        }    }}

总结

上述示例展示了最简单的文件NIO和网络NIO用法，接下来会深入分析每个方法的源码，并对性能进行调优。

原文链接：https://yq.aliyun.com/articles/707061?utm_content=g_1000067871

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