BIO

当确定客户端连接数很少时，BIO也可以使用，简单不易出错，效率低下不代表没有用武之地。

BIO的accept,read,write都是阻塞的，一个线程老在那阻塞着，其实它没干事，但是它脑门上贴着一个“I`m busying”我很忙，效率极其低下，即使用线程池还不是一堆线程在那"Busy"

server端：

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

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket ss = new ServerSocket();
        ss.bind(new InetSocketAddress("127.0.0.1", 8888));
        while(true) {
            Socket s = ss.accept(); //阻塞方法

            new Thread(() -> {
                handle(s);
            }).start();
        }

    }

    static void handle(Socket s) {
        try {
            byte[] bytes = new byte[1024];
            int len = s.getInputStream().read(bytes);
            System.out.println(new String(bytes, 0, len));

            s.getOutputStream().write(bytes, 0, len);
            s.getOutputStream().flush();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

client端：

import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;

public class Client {
    public static void main(String[] args) throws IOException {
        Socket s = new Socket("127.0.0.1", 8888);
        s.getOutputStream().write("HelloServer".getBytes());
        s.getOutputStream().flush();
        //s.getOutputStream().close();
        System.out.println("write over, waiting for msg back...");
        byte[] bytes = new byte[1024];
        int len = s.getInputStream().read(bytes);
        System.out.println(new String(bytes, 0, len));
        s.close();
    }
}

NIO

单线程模型

selector选择器大管家，专门做监听这件事，监听连接、读、写事件。

只需要一个连接就可以处理客户端的连接，客户端的读，客户端的写，selector全部都能处理。

使用到的设计模式就是observer观察者模式。

selector说：我对某些事感兴趣，哪些事呢？关于客户端的连接、读、写这些事我统统感兴趣！我会每隔一段时间就去检查server这些事件有没有发生，如果有一个客户端要连接了，selector就帮助客户端和server建立连接，来一个就帮忙建立一个连接，来一个建一个。selector除了负责客户端的连接之外，还会盯着已经连接好的客户端通道有没有需要读和写的数据，需要读就读过来，需要写就写出去。

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;
import java.util.Set;

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocketChannel ssc = ServerSocketChannel.open();
        ssc.socket().bind(new InetSocketAddress("127.0.0.1", 8888));
        ssc.configureBlocking(false);

        System.out.println("server started, listening on :" + ssc.getLocalAddress());
        Selector selector = Selector.open();
        ssc.register(selector, SelectionKey.OP_ACCEPT);

        while(true) {
            selector.select();
            Set<SelectionKey> keys = selector.selectedKeys();
            Iterator<SelectionKey> it = keys.iterator();
            while(it.hasNext()) {
                SelectionKey key = it.next();
                it.remove();
                handle(key);
            }
        }

    }

    private static void handle(SelectionKey key) {
        if(key.isAcceptable()) {
            try {
                ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                SocketChannel sc = ssc.accept();
                sc.configureBlocking(false);
                //new Client
                //
                //String hostIP = ((InetSocketAddress)sc.getRemoteAddress()).getHostString();

			/*
			log.info("client " + hostIP + " trying  to connect");
			for(int i=0; i<clients.size(); i++) {
				String clientHostIP = clients.get(i).clientAddress.getHostString();
				if(hostIP.equals(clientHostIP)) {
					log.info("this client has already connected! is he alvie " + clients.get(i).live);
					sc.close();
					return;
				}
			}*/

                sc.register(key.selector(), SelectionKey.OP_READ );
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
            }
        } else if (key.isReadable()) { //flip
            SocketChannel sc = null;
            try {
                sc = (SocketChannel)key.channel();
                ByteBuffer buffer = ByteBuffer.allocate(512);
                buffer.clear();
                int len = sc.read(buffer);

                if(len != -1) {
                    System.out.println(new String(buffer.array(), 0, len));
                }

                ByteBuffer bufferToWrite = ByteBuffer.wrap("HelloClient".getBytes());
                sc.write(bufferToWrite);
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                if(sc != null) {
                    try {
                        sc.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

Reactor模型

引入了线程池，selector领着一帮工人在干活，成了一个包工头，不再是一个人单打独斗了。

selector就是一个boss，只负责客户端的连接，线程池就是worker，需要读写了就交给worker来处理，worker中谁闲着就交给谁来处理，而不是像NIO单线程模型一样有读有写了就new一个工人出来。

代码实现

import java.io.ByteArrayOutputStream;
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;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class PoolServer {

    ExecutorService pool = Executors.newFixedThreadPool(50);

    private Selector selector;
    //中文测试

    /**
     *
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {
        PoolServer server = new PoolServer();
        server.initServer(8000);
        server.listen();
    }

    /**
     *
     * @param port
     * @throws IOException
     */
    public void initServer(int port) throws IOException {
        //
        ServerSocketChannel serverChannel = ServerSocketChannel.open();
        //
        serverChannel.configureBlocking(false);
        //
        serverChannel.socket().bind(new InetSocketAddress(port));
        //
        this.selector = Selector.open();

        serverChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("服务端启动成功！");
    }

    /**
     *
     * @throws IOException
     */
    @SuppressWarnings("unchecked")
    public void listen() throws IOException {
        // 轮询访问selector  
        while (true) {
            //
            selector.select();
            //
            Iterator ite = this.selector.selectedKeys().iterator();
            while (ite.hasNext()) {
                SelectionKey key = (SelectionKey) ite.next();
                //
                ite.remove();
                //
                if (key.isAcceptable()) {
                    ServerSocketChannel server = (ServerSocketChannel) key.channel();
                    //
                    SocketChannel channel = server.accept();
                    //
                    channel.configureBlocking(false);
                    //
                    channel.register(this.selector, SelectionKey.OP_READ);
                    //
                } else if (key.isReadable()) {
                    //
                    key.interestOps(key.interestOps()&(~SelectionKey.OP_READ));
                    //
                    pool.execute(new ThreadHandlerChannel(key));
                }
            }
        }
    }
}

/**
 *
 * @param
 * @throws IOException
 */
class ThreadHandlerChannel extends Thread{
    private SelectionKey key;
    ThreadHandlerChannel(SelectionKey key){
        this.key=key;
    }
    @Override
    public void run() {
        //
        SocketChannel channel = (SocketChannel) key.channel();
        //
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        //
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            int size = 0;
            while ((size = channel.read(buffer)) > 0) {
                buffer.flip();
                baos.write(buffer.array(),0,size);
                buffer.clear();
            }
            baos.close();
            //
            byte[] content=baos.toByteArray();
            ByteBuffer writeBuf = ByteBuffer.allocate(content.length);
            writeBuf.put(content);
            writeBuf.flip();
            channel.write(writeBuf);//
            if(size==-1){

                channel.close();
            }else{
                //
                key.interestOps(key.interestOps()|SelectionKey.OP_READ);
                key.selector().wakeup();
            }
        }catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

AIO

NIO需要不停地轮询server有没有事件发生。

AIO大概是这样的：有客户端要连接的时候，交给操作系统OS去连接，OS一旦连接上客户端，就会给大管家selector发一消息说有人要连上来，要不要给它连，大管家可以有多个，但一般是一个，它只负责连接客户端，跟NIO不同的是，selector只需要在那里坐着等就行，不用转圈去轮询server。

AIO与NIO底层都是使用OS的epoll系统调用函数实现的，epoll就是轮询，而NIO也是轮询，所以netty就直接封装了NIO，其API封装的更像是AIO。

Windows实现的AIO是真正的AIO异步IO，效率要比Linux要高。但是服务器大多数选择的是Linux而非Windows。

AIO用到的设计模式是钩子函数（模板方法）。

并不是线程数越多越好，线程数太多会增加线程切换的开销。

IO都是OS操作系统来实现的，要不然你程序可以随便往硬盘里写点东西，不经过OS老大也太放肆了吧？

单线程AIO代码实现

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;

public class Server {
    public static void main(String[] args) throws Exception {
        final AsynchronousServerSocketChannel serverChannel = AsynchronousServerSocketChannel.open()
                .bind(new InetSocketAddress(8888));

        serverChannel.accept(null, new CompletionHandler<AsynchronousSocketChannel, Object>() {
            @Override
            public void completed(AsynchronousSocketChannel client, Object attachment) {
                serverChannel.accept(null, this);
                try {
                    System.out.println(client.getRemoteAddress());
                    ByteBuffer buffer = ByteBuffer.allocate(1024);
                    client.read(buffer, buffer, new CompletionHandler<Integer, ByteBuffer>() {
                        @Override
                        public void completed(Integer result, ByteBuffer attachment) {
                            attachment.flip();
                            System.out.println(new String(attachment.array(), 0, result));
                            client.write(ByteBuffer.wrap("HelloClient".getBytes()));
                        }

                        @Override
                        public void failed(Throwable exc, ByteBuffer attachment) {
                            exc.printStackTrace();
                        }
                    });


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

            @Override
            public void failed(Throwable exc, Object attachment) {
                exc.printStackTrace();
            }
        });

        while (true) {
            Thread.sleep(1000);
        }

    }
}

线程池AIO代码实现

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousChannelGroup;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ServerWithThreadGroup {
    public static void main(String[] args) throws Exception {

        ExecutorService executorService = Executors.newCachedThreadPool();
        AsynchronousChannelGroup threadGroup = AsynchronousChannelGroup.withCachedThreadPool(executorService, 1);

        //中文测试
        final AsynchronousServerSocketChannel serverChannel = AsynchronousServerSocketChannel.open(threadGroup)
                .bind(new InetSocketAddress(8888));

        serverChannel.accept(null, new CompletionHandler<AsynchronousSocketChannel, Object>() {
            @Override
            public void completed(AsynchronousSocketChannel client, Object attachment) {
                serverChannel.accept(null, this);
                try {
                    System.out.println(client.getRemoteAddress());
                    ByteBuffer buffer = ByteBuffer.allocate(1024);
                    client.read(buffer, buffer, new CompletionHandler<Integer, ByteBuffer>() {
                        @Override
                        public void completed(Integer result, ByteBuffer attachment) {
                            attachment.flip();
                            System.out.println(new String(attachment.array(), 0, result));
                            client.write(ByteBuffer.wrap("HelloClient".getBytes()));
                        }

                        @Override
                        public void failed(Throwable exc, ByteBuffer attachment) {
                            exc.printStackTrace();
                        }
                    });


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

            @Override
            public void failed(Throwable exc, Object attachment) {
                exc.printStackTrace();
            }
        });

        while (true) {
            Thread.sleep(1000);
        }

    }
}

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Java IO模型--BIO、NIO Single Thread、NIO Reactor、AIO单线程及多线程AIO

BIO

server端：

client端：

NIO

单线程模型

Reactor模型

代码实现

AIO

单线程AIO代码实现

线程池AIO代码实现

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