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Java IO系列之四:NIO通信模型

分布式rpc框架有很多,比如dubbo,netty,还有很多其他的产品。但他们大部分都是基于nio的,

nio是非阻塞的io,那么它的内部机制是怎么实现的呢。

1.由一个专门的线程处理所有IO事件,并负责分发。

2.事件驱动机制,事件到来的时候触发操作,不需要阻塞的监视事件。

3.线程之前通过wait,notify通信,减少线程切换。

 

NIO使用步骤

服务端步骤:

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.UnknownHostException;
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;

public class NIOServer {
    public static void main(String[] args) throws IOException {
        new Thread(new ReactorTask()).start();
    }

    public static class ReactorTask implements Runnable {
        private Selector selector;
        public ReactorTask() {
            try {
                // 第一步:打开ServerSocketChannel,用于监听客户端的连接,它是所有客户端连接的父管道
                ServerSocketChannel acceptorSvr = ServerSocketChannel.open();

                // 第二步:绑定监听端口,设置连接为非阻塞模式
                acceptorSvr.socket().bind(new InetSocketAddress(InetAddress.getByName("localhost"), 1234));
                acceptorSvr.configureBlocking(false);

                // 第三步:创建Reactor线程,创建多路复用器并启动线程
                selector = Selector.open();

                // 第四步:将ServerSocketChannel注册到Reactor线程的多路复用器Selector上,监听Accept事件
                SelectionKey key = acceptorSvr.register(selector, SelectionKey.OP_ACCEPT);

            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void run() {
            // 第五步:在run方法中无限循环体内轮询准备就绪的Key
            while (true) {
                try {
                    selector.select(1000);
                    Set<SelectionKey> selectedKeys = selector.selectedKeys();
                    Iterator<SelectionKey> it = selectedKeys.iterator();
                    SelectionKey key = null;
                    while (it.hasNext()) {
                        key = it.next();
                        it.remove();
                        try {
                            if (key.isValid()) {
                                // 处理新接入的请求消息
                                if (key.isAcceptable()) {
                                    // 第六步:多路复用器监听到有新的客户端接入,处理新的接入请求,完成TCP三次握手,建立物理链路
                                    ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                                    SocketChannel sc = ssc.accept();
                                    // 第七步:设置客户端链路为非阻塞模式
                                    sc.configureBlocking(false);
                                    sc.socket().setReuseAddress(true);
                                    // 第八步:将新接入的客户端连接注册到Reactor线程的多路复用器上,监听读操作,读取客户端发送的网络消息
                                    sc.register(selector, SelectionKey.OP_READ);
                                }
                                if (key.isReadable()) {
                                    // 第九步:异步读取客户端请求消息到缓存区
                                    SocketChannel sc = (SocketChannel) key.channel();
                                    ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                                    int readBytes = sc.read(readBuffer);

                                    // 第十步:对ByteBuffer进行编解码,如果有半包消息指针reset,继续读取后续的报文
                                    if (readBytes > 0) {
                                        readBuffer.flip();
                                        byte[] bytes = new byte[readBuffer.remaining()];
                                        readBuffer.get(bytes);
                                        String body = new String(bytes, "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";
                                        //写应答
                                        byte[] bytes2 = currentTime.getBytes();
                                        ByteBuffer writeBuffer = ByteBuffer.allocate(bytes2.length);
                                        writeBuffer.put(bytes2);
                                        writeBuffer.flip();
                                        sc.write(writeBuffer);
                                    } else if (readBytes < 0) {
                                        // 对端链路关闭
                                        key.cancel();
                                        sc.close();
                                    } else
                                        ; // 读到0字节,忽略
                                }
                            }
                        } catch (Exception e) {
                            if (key != null) {
                                key.cancel();
                                if (key.channel() != null)
                                    key.channel().close();
                            }
                        }
                    }
                } catch (Throwable t) {
                    t.printStackTrace();
                }
            }
        }
    }
}

注意:如果发送区TCP缓冲区满,会导致写半包,此时,需要注册监听写操作位,循环写,直到整包消息写入TCP缓冲区

客户端步骤:

 

客户端:

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;
import java.util.Set;

public class TimeClientHandle implements Runnable {

    private String host;
    private int port;
private Selector selector; private SocketChannel socketChannel; private volatile boolean stop; public TimeClientHandle(String host, int port) { this.host = host == null ? "127.0.0.1" : host; this.port = port; try { //第一步:打开SocketChannel,用于创建客户端连接 socketChannel = SocketChannel.open(); //第二步:设置SocketChannel为非阻塞模式 socketChannel.configureBlocking(false); //第三步:创建多路复用器(在Reactor线程中) selector = Selector.open(); } catch (IOException e) { e.printStackTrace(); System.exit(1); } } @Override public void run() { try { // 第四步:socketChannel发起连接 if (socketChannel.connect(new InetSocketAddress(host, port))) { //第五步:如果直接连接成功,则注册到多路复用器上 socketChannel.register(selector, SelectionKey.OP_READ); //第六步:发送请求消息,读应答 byte[] req = "QUERY TIME ORDER".getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(req.length); writeBuffer.put(req); writeBuffer.flip(); socketChannel.write(writeBuffer); if (!writeBuffer.hasRemaining()) System.out.println("Send order 2 server succeed."); } else socketChannel.register(selector, SelectionKey.OP_CONNECT); } catch (IOException e) { e.printStackTrace(); System.exit(1); } while (!stop) { try { //第七步:多路复用器在run的无限循环体内轮询准备就绪的Key selector.select(1000); Set<SelectionKey> selectedKeys = selector.selectedKeys(); Iterator<SelectionKey> it = selectedKeys.iterator(); SelectionKey key = null; while (it.hasNext()) { key = it.next(); it.remove(); try { if (key.isValid()) { //第八步:将连接成功的Channel注册到多路复用器上 // 判断是否连接成功 SocketChannel sc = (SocketChannel) key.channel(); if (key.isConnectable()) { if (sc.finishConnect()) { sc.register(selector, SelectionKey.OP_READ); //发送请求消息,读应答 byte[] req = "QUERY TIME ORDER".getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(req.length); writeBuffer.put(req); writeBuffer.flip(); sc.write(writeBuffer); if (!writeBuffer.hasRemaining()) System.out.println("Send order 2 server succeed."); } else System.exit(1);// 连接失败,进程退出 } //监听读操作,读取服务端写回的网络信息 if (key.isReadable()) { //第九步:读取信息到缓冲区 ByteBuffer readBuffer = ByteBuffer.allocate(1024); int readBytes = sc.read(readBuffer); if (readBytes > 0) { readBuffer.flip(); byte[] bytes = new byte[readBuffer.remaining()]; readBuffer.get(bytes); String body = new String(bytes, "UTF-8"); System.out.println("Now is : " + body); this.stop = true; } else if (readBytes < 0) { // 对端链路关闭 key.cancel(); sc.close(); } else ; // 读到0字节,忽略 } } } catch (Exception e) { if (key != null) { key.cancel(); if (key.channel() != null) key.channel().close(); } } } } catch (Exception e) { e.printStackTrace(); System.exit(1); } } // 多路复用器关闭后,所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭,所以不需要重复释放资源 if (selector != null) try { selector.close(); } catch (IOException e) { e.printStackTrace(); } } } package com.dxz.springsession.nio.demo6; public class TimeClient { /** * @param args */ public static void main(String[] args) { int port = 1234; if (args != null && args.length > 0) { try { port = Integer.valueOf(args[0]); } catch (NumberFormatException e) { // 采用默认值 } } new Thread(new TimeClientHandle("127.0.0.1", port), "TimeClient-001") .start(); } }

 

 抄录地址:

  1. Java NIO系列教程(一) Java NIO 概述
  2. java nio详解
  3. java NIO 运行原理介绍

 

posted @ 2019-04-23 14:56  海米傻傻  阅读(...)  评论(...编辑  收藏