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Java中的异步非阻塞AIO模型详解

作者:超大充电宝

这篇文章主要介绍了Java中的异步非阻塞AIO模型详解,AIO需要操作系统的支持,在linux内核2.6版本中加入了对真正异步IO的支持,java从jdk1.7开始支持AIO,本文提供了部分实现代码,需要的朋友可以参考下

1、AIO:异步非阻塞简介

AIO需要操作系统的支持,在linux内核2.6版本中加入了对真正异步IO的支持,java从jdk1.7开始支持AIO

核心类有AsynchronousSocketChannel 、AsynchronousServerSocketChannel、AsynchronousChannelGroup

AsynchronousChannelGroup是异步Channel的分组管理器,它可以实现资源共享。

创建AsynchronousChannelGroup时,需要传入一个ExecutorService,也就是绑定一个线程池,该线程池负责两个任务:处理IO事件和触发CompletionHandler回调接口。

2、AsynchronousServerSocketChannel:AIO中网络通信服务端Socket

accept() 方法: AsynchronousServerSocketChannel创建成功后,类似于ServerSocket,也是调用 accept() 方法来接受来自客户端的连接, 由于异步IO实际的IO操作是交给操作系统来做的,用户进程只负责通知操作系统进行IO和接受操作系统IO完成的通知。 所以异步的ServerChannel调用 accept() 方法后,当前线程不会阻塞, 程序也不知道accept()方法什么时候能够接收到客户端请求并且操作系统完成网络IO, 为解决这个问题,AIO为accept()方法提供两个版本:

Future<AsynchronousSocketChannel> accept() :
开始接收客户端请求,如果当前线程需要进行网络IO(即获得AsynchronousSocketChannel),则应该调用该方法返回的Future对象的get()方法,但是get()方法会阻塞该线程,所以这种方式是阻塞式的异步IO。

<&nbsp;A&nbsp;> void accept (Aattachment,CompletionHandler<AsynchronousSocketChannel,? super A> handler):
开始接受来自客户端请求,连接成功或失败都会触发CompletionHandler对象的相应方法。
其中AsynchronousSocketChannel就代表该CompletionHandler处理器在处理连接成功时的result是AsynchronousSocketChannel的实例。
而CompletionHandler接口中定义了两个方法,
completed(V result , A attachment):当IO完成时触发该方法,该方法的第一个参数代表IO操作返回的对象,
第二个参数代表发起IO操作时传入的附加参数。
faild(Throwable exc, A attachment):当IO失败时触发该方法,第一个参数代表IO操作失败引发的异常或错误。

3、AIO编程

服务端

public class AioServer {
    private static int DEFAULT_PORT = 12345;
    private static ServerHandler serverHandle;
    public volatile static long clientCount = 0;
    public static void start(){
        start(DEFAULT_PORT);
    }
    public static synchronized void start(int port){
        if(serverHandle!=null)
            return;
        serverHandle = new ServerHandler(port);
        new Thread(serverHandle,"Server").start();
    }
    public static void main(String[] args) {
        AioServer.start();
    }
}
public class ServerHandler implements Runnable{
    private AsynchronousServerSocketChannel channel;
    public ServerHandler(int port) {
        try {
            //创建服务端通道
            channel = AsynchronousServerSocketChannel.open();
            //绑定端口
            channel.bind(new InetSocketAddress(port));
            System.out.println("服务端已启动,端口号:"+port);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void run() {
        channel.accept(this, new AcceptHandler());
//        Future <AsynchronousSocketChannel> accept = channel.accept();
        //该步操作是异步操作 防止当前线程直接执行结束
        //方案1: while(true)+sleep
        while (true) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
//        //方案2 CountDownLatch 作用:在完成一组正在执行的操作之前,允许当前的现场一直阻塞 此处,让现场在此阻塞,防止服务端执行完成后退出
//
//        CountDownLatch count = new CountDownLatch(1);
//        channel.accept(this, new AcceptHandler());
//        try {
//            count.await();
//        } catch (InterruptedException e) {
//            e.printStackTrace();
//        }
    }
    // CompletionHandler<V,A>
    // V-IO操作的结果,这里是成功建立的连接,AsynchronousSocketChannel
   // A-IO操作附件,这里传入AsynchronousServerSocketChannel便于继续接收请求建立新连接
    class AcceptHandler implements CompletionHandler<AsynchronousSocketChannel, ServerHandler> {
        @Override
        public void completed(AsynchronousSocketChannel channel, ServerHandler serverHandler) {
            //创建新的Buffer
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            //异步读  第三个参数为接收消息回调的业务Handler
//            channel.read(buffer, buffer, new ReadHandler(channel));
            //继续接受其他客户端请求
            serverHandler.channel.accept(null, this);
        }
        @Override
        public void failed(Throwable exc, ServerHandler serverHandler) {
            exc.printStackTrace();
        }
    }
    class ReadHandler implements CompletionHandler<ByteBuffer, ByteBuffer> {
        //用户读取或者发送消息的channel
        private AsynchronousSocketChannel channel;
        public ReadHandler(AsynchronousSocketChannel channel) {
            this.channel = channel;
        }
        @Override
        public void completed(ByteBuffer result, ByteBuffer attachment) {
            result.flip();
            byte[] msg = new byte[result.remaining()];
            result.get(msg);
            try {
                String expression = new String(msg, "UTF-8");
                System.out.println("服务器收到消息: " + expression);
//                String result1 = "服务端收到消息\n";
                result.clear();
                //向客户端发送消息
                doWrite(expression);
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }
        //发送消息
        private void doWrite(String msg) {
            byte[] bytes = msg.getBytes();
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            buffer.put(bytes);
            buffer.flip();
            //异步写数据
            channel.write(buffer, buffer, new CompletionHandler <Integer, ByteBuffer>() {
                @Override
                public void completed(Integer result, ByteBuffer attachment) {
                    //如果没有发送完,继续发送
                    if (attachment.hasRemaining()) {
                        channel.write(attachment, attachment, this);
                    } else {
                        //创建新的Buffer
                        ByteBuffer allocate = ByteBuffer.allocate(1024);
                        //异步读 第三个参数为接收消息回调的业务Handler
//                        channel.read(allocate, attachment, new ReadHandler(channel));
                    }
                }
                @Override
                public void failed(Throwable exc, ByteBuffer attachment) {
                    exc.printStackTrace();
                    try {
                        channel.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        @Override
        public void failed(Throwable exc, ByteBuffer attachment) {
            exc.printStackTrace();
            try {
                channel.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

客户端

public class AioClient {
    private static String DEFAULT_HOST = "127.0.0.1";
    private static int DEFAULT_PORT = 12345;
    private static ClientHandler clientHandle;
    public static void start(){
        start(DEFAULT_HOST,DEFAULT_PORT);
    }
    public static synchronized void start(String ip,int port){
        if(clientHandle!=null)
            return;
        clientHandle = new ClientHandler(ip,port);
        new Thread(clientHandle,"Client").start();
    }
    //向服务器发送消息
    public static boolean sendMsg(String msg) throws Exception{
        if(msg.equals("exit")) return false;
        clientHandle.sendMsg(msg);
        return true;
    }
    public static void main(String[] args) throws Exception{
        AioClient.start();
        System.out.println("请输入请求消息:");
        Scanner scanner = new Scanner(System.in);
        while(AioClient.sendMsg(scanner.nextLine()));
    }
}
public class ClientHandler implements Runnable{
    private AsynchronousSocketChannel clientChannel;
    private String host;
    private int port;
    private CountDownLatch latch;
    public ClientHandler(String host, int port) {
        this.host = host;
        this.port = port;
        try {
            //创建异步的客户端通道
            clientChannel = AsynchronousSocketChannel.open();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void run() {
        //创建CountDownLatch等待
//        latch = new CountDownLatch(1);
        //发起异步连接操作,回调参数就是这个类本身,如果连接成功会回调completed方法
        clientChannel.connect(new InetSocketAddress(host, port), this, new AcceptHandler());
        while (true) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
//        try {
//            latch.await();
//        } catch (InterruptedException e1) {
//            e1.printStackTrace();
//        }
//        try {
//            clientChannel.close();
//        } catch (IOException e) {
//            e.printStackTrace();
//        }
    }
    //向服务器发送消息
    public void sendMsg(String msg){
        byte[] req = msg.getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
        System.out.println(">>>>>>msg:"+msg);
        writeBuffer.put(req);
        writeBuffer.flip();
        //异步写
        clientChannel.write(writeBuffer, writeBuffer,new WriteHandler(clientChannel));
    }
    /**
     * 接收类
     */
    class AcceptHandler implements CompletionHandler<Void, ClientHandler> {
        public AcceptHandler() {}
        @Override
        public void completed(Void result, ClientHandler attachment) {
            System.out.println("连接服务器成功");
    }
        @Override
        public void failed(Throwable exc, ClientHandler attachment) {
            exc.printStackTrace();
            try {
                attachment.clientChannel.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    class WriteHandler implements CompletionHandler<Integer, ByteBuffer> {
        private AsynchronousSocketChannel channel;
        public WriteHandler(AsynchronousSocketChannel channel) {
            this.channel = channel;
        }
        @Override
        public void completed(Integer result, ByteBuffer attachment) {
            //完成全部数据的写入
            if (attachment.hasRemaining()) {
                //数据没有写完,继续写
                System.out.println("WriteHandler.hasRemaining>>>>>");
                clientChannel.write(attachment, attachment, this);
            } else {
                //读取数据
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                clientChannel.read(readBuffer, readBuffer, new ReadHandler(clientChannel));
            }
        }
        @Override
        public void failed(Throwable exc, ByteBuffer attachment) {
            exc.printStackTrace();
            try {
                channel.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    class ReadHandler implements CompletionHandler<Integer, ByteBuffer> {
        private AsynchronousSocketChannel clientChannel;
        public ReadHandler(AsynchronousSocketChannel clientChannel) {
            this.clientChannel = clientChannel;
        }
        @Override
        public void completed(Integer result,ByteBuffer buffer) {
            buffer.flip();
            byte[] bytes = new byte[buffer.remaining()];
            buffer.get(bytes);
            String body;
            try {
                body = new String(bytes,"UTF-8");
                System.out.println("客户端收到结果:"+ body);
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }
        @Override
        public void failed(Throwable exc,ByteBuffer attachment) {
            System.err.println("数据读取失败...");
            try {
                clientChannel.close();
            } catch (IOException e) {
            }
        }
    }
}

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