package com.ddcx.utils;

/**
 * @author: xc
 * @ClassName: Test
 * @Date: 2021-03-03 12:47
 * @Description:
 */

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

class Reactor implements Runnable {
    final Selector selector;
    final ServerSocketChannel serverSocket;

    Reactor(int port) throws IOException { //Reactor初始化
        selector = Selector.open();
        serverSocket = ServerSocketChannel.open();
        //要监听的网络端口号
        serverSocket.socket().bind(new InetSocketAddress(port));
        //非阻塞
        serverSocket.configureBlocking(false);
        //分步处理,第一步,接收accept事件
        SelectionKey sk =
                serverSocket.register(selector, SelectionKey.OP_ACCEPT);
        //attach callback object, Acceptor
        sk.attach(new Acceptor());
    }

    @Override
    public void run() {
        try {
            while (!Thread.interrupted()) {
                //阻塞到至少有一个通道在你注册的事件上就绪了。 
                selector.select();
                Set selected = selector.selectedKeys();
                Iterator it = selected.iterator();
                while (it.hasNext()) {
                    //Reactor负责dispatch收到的事件
                    dispatch((SelectionKey) (it.next()));
                }
                selected.clear();
            }
        } catch (IOException ex) { /* ... */ }
    }

    void dispatch(SelectionKey k) {
        Runnable r = (Runnable) (k.attachment());
        //调用之前注册的callback对象
        if (r != null) {
            //这里是Acceptor的run方法
            r.run();
        }
    }

    // inner class
    class Acceptor implements Runnable {

        @Override
        public void run() {
            try {
                //阻塞到获取网络连接通道
                SocketChannel channel = serverSocket.accept();
                if (channel != null) {
                    //连接已经就绪,将相应的感兴趣的读写事件注册到回调中
                    new ReadHander(selector, channel);
                }
            } catch (IOException ex) { /* ... */ }
        }
    }


    public static void main(String[] args) throws IOException {
        Reactor reactor = new Reactor(9000);
        reactor.run();
    }
}


package com.ddcx.utils;

/**
 * @author: xc
 * @ClassName: ReadHander
 * @Date: 2021-03-03 12:48
 * @Description:
 */

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;

class ReadHander implements Runnable {
    final SocketChannel channel;
    final SelectionKey sk;
    ByteBuffer input = ByteBuffer.allocate(90);
    ByteBuffer output = ByteBuffer.allocate(400);
    static final int READING = 0, SENDING = 1;
    int state = READING;

    ReadHander(Selector selector, SocketChannel c) throws IOException {
        channel = c;
        c.configureBlocking(false);
        // Optionally try first read now
        sk = channel.register(selector, 0);

        //将Handler作为callback对象
        sk.attach(this);

        //第二步,注册Read就绪事件
        sk.interestOps(SelectionKey.OP_READ);
        selector.wakeup();
    }

    boolean inputIsComplete() {
        /* ... */
        return false;
    }

    boolean outputIsComplete() {

        /* ... */
        return false;
    }

    void process() {
        /* ... */
        return;
    }

    @Override
    public void run() {
        try {
            if (state == READING) {
                read();
            } else if (state == SENDING) {
                send();
            }
        } catch (IOException ex) { /* ... */ }
    }

    void read() throws IOException {
        channel.read(input);
        if (inputIsComplete()) {
            process();
            state = SENDING;
            // Normally also do first write now
            //第三步,接收write就绪事件
            sk.interestOps(SelectionKey.OP_WRITE);
        }
    }

    void send() throws IOException {
        channel.write(output);

        //write完就结束了, 关闭select key
        if (outputIsComplete()) {
            sk.cancel();
        }
    }
}

①.通过Selector的select（）方法可以选择已经准备就绪的通道

②.通过ServerSocketChannel.accept()方法监听新进来的连接。当accept()方法返回的时候，它返回一个包含新进来的连接的SocketChannel。因此， accept()方法会一直阻塞到有新连接到达。通常不会仅仅只监听一个连接

单线程版 Reactor模型,其实就是做了一件事情,就是把要监听的socket端口注册到selector中去,并且轮询线程内可以获取到多个已经准备就绪的socket连接通道,同时进行处理这些事件

?

2. 多线程Reactor模型

多线程主要体现在handler处理的时候,因为处理的事件可能耗时相对于久一些,这样做可以更快的处理感兴趣的事件

selectionKey.attach(new HandlerThreadPool(socketChannel));