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