【从入门到放弃-Java】并发编程-NIO使用

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。

更多文章见:https://nc2era.com

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