Java IO系列之四：NIO通信模型

分布式rpc框架有很多，比如dubbo,netty,還有很多其他的產品。但他們大部分都是基於nio的，

nio是非阻塞的io,那么它的內部機制是怎么實現的呢。

1.由一個專門的線程處理所有IO事件，並負責分發。

2.事件驅動機制，事件到來的時候觸發操作，不需要阻塞的監視事件。

3.線程之前通過wait,notify通信，減少線程切換。

 

NIO使用步驟

服務端步驟：

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：打開ServerSocketChannel，用於監聽客戶端的連接，它是所有客戶端連接的父管道
                ServerSocketChannel acceptorSvr = ServerSocketChannel.open();

                // 第二步：綁定監聽端口，設置連接為非阻塞模式
                acceptorSvr.socket().bind(new InetSocketAddress(InetAddress.getByName("localhost"), 1234));
                acceptorSvr.configureBlocking(false);

                // 第三步：創建Reactor線程，創建多路復用器並啟動線程
                selector = Selector.open();

                // 第四步：將ServerSocketChannel注冊到Reactor線程的多路復用器Selector上，監聽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方法中無限循環體內輪詢准備就緒的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()) {
                                // 處理新接入的請求消息
                                if (key.isAcceptable()) {
                                    // 第六步：多路復用器監聽到有新的客戶端接入，處理新的接入請求，完成TCP三次握手，建立物理鏈路
                                    ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                                    SocketChannel sc = ssc.accept();
                                    // 第七步：設置客戶端鏈路為非阻塞模式
                                    sc.configureBlocking(false);
                                    sc.socket().setReuseAddress(true);
                                    // 第八步：將新接入的客戶端連接注冊到Reactor線程的多路復用器上，監聽讀操作，讀取客戶端發送的網絡消息
                                    sc.register(selector, SelectionKey.OP_READ);
                                }
                                if (key.isReadable()) {
                                    // 第九步：異步讀取客戶端請求消息到緩存區
                                    SocketChannel sc = (SocketChannel) key.channel();
                                    ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                                    int readBytes = sc.read(readBuffer);

                                    // 第十步：對ByteBuffer進行編解碼，如果有半包消息指針reset，繼續讀取后續的報文
                                    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";
                                        //寫應答
                                        byte[] bytes2 = currentTime.getBytes();
                                        ByteBuffer writeBuffer = ByteBuffer.allocate(bytes2.length);
                                        writeBuffer.put(bytes2);
                                        writeBuffer.flip();
                                        sc.write(writeBuffer);
                                    } else if (readBytes < 0) {
                                        // 對端鏈路關閉
                                        key.cancel();
                                        sc.close();
                                    } else
                                        ; // 讀到0字節，忽略
                                }
                            }
                        } catch (Exception e) {
                            if (key != null) {
                                key.cancel();
                                if (key.channel() != null)
                                    key.channel().close();
                            }
                        }
                    }
                } catch (Throwable t) {
                    t.printStackTrace();
                }
            }
        }
    }
}

注意：如果發送區TCP緩沖區滿，會導致寫半包，此時，需要注冊監聽寫操作位，循環寫，直到整包消息寫入TCP緩沖區

客戶端步驟：

 

客戶端：

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：打開SocketChannel,用於創建客戶端連接
            socketChannel = SocketChannel.open();
            //第二步：設置SocketChannel為非阻塞模式
            socketChannel.configureBlocking(false);
            //第三步：創建多路復用器（在Reactor線程中）
            selector = Selector.open();
            
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    @Override
    public void run() {
        try {
            // 第四步：socketChannel發起連接
            if (socketChannel.connect(new InetSocketAddress(host, port))) {
                //第五步：如果直接連接成功，則注冊到多路復用器上
                socketChannel.register(selector, SelectionKey.OP_READ);
                //第六步：發送請求消息，讀應答
                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：多路復用器在run的無限循環體內輪詢准備就緒的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：將連接成功的Channel注冊到多路復用器上
                            // 判斷是否連接成功
                            SocketChannel sc = (SocketChannel) key.channel();
                            if (key.isConnectable()) {
                                if (sc.finishConnect()) {
                                    sc.register(selector, SelectionKey.OP_READ);
                                    //發送請求消息，讀應答
                                    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);// 連接失敗，進程退出
                            }
                            //監聽讀操作，讀取服務端寫回的網絡信息
                            if (key.isReadable()) {
                                //第九步：讀取信息到緩沖區
                                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) {
                                    // 對端鏈路關閉
                                    key.cancel();
                                    sc.close();
                                } else
                                    ; // 讀到0字節，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);
            }
        }

        // 多路復用器關閉后，所有注冊在上面的Channel和Pipe等資源都會被自動去注冊並關閉，所以不需要重復釋放資源
        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) {
        // 采用默認值
        }
    }
    new Thread(new TimeClientHandle("127.0.0.1", port), "TimeClient-001")
        .start();
    }
}

 

 抄錄地址：

1. Java NIO系列教程（一） Java NIO 概述
2. java nio詳解
3. java NIO 運行原理介紹