NIO2.0 AIO入門

NIO 2.0引入了新的異步通道的概念，並提供了異步文件通道和異步套接字通道的實現。異步通道提供一下兩種方式獲取操作結果。

1. 通過java.util.concurrent.Future類來表示異步操作的結果；
2. 在執行異步操作的時候傳入一個java.nio.channels。
   CompletionHandler接口的實現類作爲操作完成的回調

NIO 2.0的異步套接字通道是真正的異步非阻塞I/O，對應於UNIX網絡編程中的事件驅動I/O(AIO)。它不需要通過多路複用器(Selector)對註冊的通道進行輪詢操作即可實現異步讀寫，從而簡化了NIO的編程模型。

簡單的說，NIO1.0 和NIO2.0 相比最大的區別是NIO1.0通過多路複用器輪詢來獲取讀寫事件，然後執行具體的操作，NIO2.0採用和Future和回調，使用上更加簡潔。

下面是一個例子，客戶端向服務端發一個時間查詢消息，服務端返回查詢的結果。
eg
服務端：

public class TimeServer {
    public static void main(String[] args) {
        AsyncTimeServerHandler asyncTimeServerHandler=new AsyncTimeServerHandler(8080);
        new Thread(asyncTimeServerHandler,"AI0-SERVER").start();
    }
}

public class AsyncTimeServerHandler implements Runnable {
    private int port;
    CountDownLatch latch;
    AsynchronousServerSocketChannel asynchronousServerSocketChannel;

    AsyncTimeServerHandler(int port) {
        this.port = port;
        try {
            //創建一個服務端通道
            asynchronousServerSocketChannel = AsynchronousServerSocketChannel.open();
            //綁定監聽端口
            asynchronousServerSocketChannel.bind(new InetSocketAddress(port));
            System.out.println("The time server is start in port:" + port);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void run() {
        latch = new CountDownLatch(1);
        //接收客戶端請求
        doAccept();
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public void doAccept() {
        //註冊接收客戶端請求，接收到請求會回調acceptCompletionHandler類
        asynchronousServerSocketChannel.accept(this, new AcceptCompletionHandler());
    }
}

public class AcceptCompletionHandler implements CompletionHandler<AsynchronousSocketChannel, AsyncTimeServerHandler> {
    @Override
    public void completed(AsynchronousSocketChannel result, AsyncTimeServerHandler attachment) {
        //接收到客戶端請求後，在註冊接收請求，用於接收其他客戶端的請求
        attachment.asynchronousServerSocketChannel.accept(attachment, this);
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        //監聽該客戶端連接上的讀請求，如果接收到消息，會調用readCompletionHandler
        result.read(buffer, buffer, new ReadCompletionHandler(result));
    }

    @Override
    public void failed(Throwable exc, AsyncTimeServerHandler attachment) {
        //接收失敗的回調
        exc.printStackTrace();
        attachment.latch.countDown();
    }
}

public class ReadCompletionHandler implements CompletionHandler<Integer,ByteBuffer>{
    private AsynchronousSocketChannel channel;

    public ReadCompletionHandler(AsynchronousSocketChannel channel){
        this.channel=channel;
    }

    @Override
    public void completed(Integer result, ByteBuffer attachment) {
        //讀取客戶端請求
        attachment.flip();
        byte[] body=new byte[attachment.remaining()];
        attachment.get(body);
        try {
            String req=new String(body,"UTF-8");
            System.out.println("The time server receive order:"+req);
            String currentTime="QUERY TIME ORDER".equalsIgnoreCase(req)?
                    new Date(System.currentTimeMillis()).toString():"BAD ORDER";
            //回覆客戶端消息
            doWrite(currentTime);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void failed(Throwable exc, ByteBuffer attachment) {
        try {
            this.channel.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void doWrite(String currentTime){
        if(currentTime!=null&&currentTime.trim().length()>0){
            byte[] bytes=currentTime.getBytes();
            ByteBuffer writeBuffer=ByteBuffer.allocate(bytes.length);
            writeBuffer.put(bytes);
            writeBuffer.flip();
            //向客戶端回覆消息
            channel.write(writeBuffer, writeBuffer,
                    new CompletionHandler<Integer, ByteBuffer>() {
                        @Override
                        public void completed(Integer result, ByteBuffer attachment) {
                            // 如果沒有發送完成，繼續發送
                            if(attachment.hasRemaining()){
                                channel.write(attachment,attachment,this);
                            }
                        }

                        @Override
                        public void failed(Throwable exc, ByteBuffer attachment) {
                            try {
                                channel.close();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }
                    });
        }
    }
}

客戶端:

public class TimeClient {
    public static void main(String[] args) {
        AsyncTimeClientHandler asyncTimeClientHandler = new AsyncTimeClientHandler("127.0.0.1", 8080);
        new Thread(asyncTimeClientHandler, "client-1").start();
    }
}

public class AsyncTimeClientHandler implements CompletionHandler<Void, AsyncTimeClientHandler>, Runnable {
    private AsynchronousSocketChannel client;
    private String host;
    private int port;
    private CountDownLatch latch;

    public AsyncTimeClientHandler(String host, int port) {
        this.host = host;
        this.port = port;
        try {
            //創建一個連接通道
            client = AsynchronousSocketChannel.open();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void run() {
        latch = new CountDownLatch(1);
        //異步連接服務端，連接成功回調this
        client.connect(new InetSocketAddress(host, port), this, this);
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        try {
            client.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void completed(Void result, AsyncTimeClientHandler attachment) {
        //連接成功發送消息
        byte[] req = "QUERY TIME ORDER".getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
        writeBuffer.put(req);
        writeBuffer.flip();
        client.write(writeBuffer, writeBuffer,
                new CompletionHandler<Integer, ByteBuffer>() {
                    @Override
                    public void completed(Integer result, ByteBuffer attachment) {
                        if (attachment.hasRemaining()) {
                            client.write(attachment, attachment, this);
                        } else {
                            ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                            //發送完消息，監聽讀消息
                            client.read(
                                    readBuffer,
                                    readBuffer,
                                    new CompletionHandler<Integer, ByteBuffer>() {
                                        @Override
                                        public void completed(Integer result, ByteBuffer attachment) {
                                            attachment.flip();
                                            byte[] bytes = new byte[attachment.remaining()];
                                            attachment.get(bytes);
                                            String body;
                                            try {
                                                body = new String(bytes, "UTF-8");
                                                System.out.println("Now is :" + body);
                                                latch.countDown();
                                            } catch (UnsupportedEncodingException e) {
                                                e.printStackTrace();
                                            }
                                        }

                                        @Override
                                        public void failed(Throwable exc, ByteBuffer attachment) {
                                            try {
                                                client.close();
                                                latch.countDown();
                                            } catch (IOException e) {
                                                e.printStackTrace();
                                            }
                                        }
                                    }
                            );
                        }
                    }

                    @Override
                    public void failed(Throwable exc, ByteBuffer attachment) {
                        try {
                            client.close();
                            latch.countDown();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                });
    }

    @Override
    public void failed(Throwable exc, AsyncTimeClientHandler attachment) {
        try {
            client.close();
            latch.countDown();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}