先看看AsynchronousServerSocketChannel來啟動(dòng)一個(gè)server，代碼如下。注意accept，無論用future還是handler，這里的調(diào)用都是非阻塞的立即返回。這里選用handler的方式，如果有客戶端連接上來，handler的會(huì)被回調(diào)。

public class AioServer {
    
    public final int port = 8080;
    public final int backlog = 2; //跟bio和nio的backlog其實(shí)是一樣的。指定accpet等待隊(duì)列的長(zhǎng)度
    private AioAcceptHandler acceptHandler;
    private AsynchronousServerSocketChannel serverSocket;
    
    public static void main(String[] args) throws Exception {
        new AioServer().startup();
    }

    private void startup() throws Exception {
        int availableProcessors = Runtime.getRuntime().availableProcessors();
        ExecutorService channelWorkers = Executors.newFixedThreadPool(availableProcessors * 2);
        AsynchronousChannelGroup channelGroup = AsynchronousChannelGroup.withCachedThreadPool(channelWorkers , 1);
        serverSocket = AsynchronousServerSocketChannel.open(channelGroup);
        serverSocket.bind(new InetSocketAddress(port), backlog);
        acceptHandler = new AioAcceptHandler();
        accept();
    }

    public void accept() {
        serverSocket.accept(this, acceptHandler); //非阻塞
    }
}

接下來CompletionHandler的接口吧，代碼如下。看到泛型的 V result 就說嘛，當(dāng)我們使用CompletionHandler的時(shí)候，自己需要清楚的知道返回結(jié)果是什么。
比如accept中指定的CompletionHandler。它是處理接受連接的，成功返回的話，結(jié)果就是套接字，那么我們就要指定泛型V的實(shí)際類型為AsynchronousSocketChannel。
再比如read方法中指定CompletionHandler。read是將數(shù)據(jù)讀取到ByteBuffer，而回調(diào)CompletionHandler的時(shí)候，結(jié)果V是讀取的數(shù)量。所以我們就要指定泛型V的實(shí)際類型為Integer。
具體可以看下面的實(shí)現(xiàn)代碼 AioAcceptHandler 和 AioReadHandler。

public interface CompletionHandler {
    //調(diào)用結(jié)果，附件
    void completed(V result, A attachment);
    //異常對(duì)象、附件
    void failed(Throwable exc, A attachment);
}

AioAcceptHandler

public class AioAcceptHandler implements CompletionHandler{

    public void completed(AsynchronousSocketChannel socket, AioServer aioServer) {
        try {
            System.out.printf("客戶端%s連接成功.
", socket.getRemoteAddress().toString());
            readData(socket);
        } catch (Exception e) {
            e.printStackTrace();
            try {
                socket.close();
            } catch (IOException e1) {}
        } finally {
            aioServer.accept();
        }
    }

    private void readData(AsynchronousSocketChannel socket) {
        ByteBuffer buf = ByteBuffer.allocate(32);   //測(cè)試時(shí)，可以不設(shè)置太大，觀察aio的多次read
        socket.read(buf, buf, new AioReadHandler(socket));
    }

    public void failed(Throwable exc, AioServer aioServer) {
        exc.printStackTrace();
    }
}

AioReadHandler

public class AioReadHandler implements CompletionHandler {

    private AsynchronousSocketChannel socket;
    private ByteArrayOutputStream baos = new ByteArrayOutputStream();
    public AioReadHandler(AsynchronousSocketChannel socket){
        this.socket = socket;
    }
    
    public void completed(Integer result, ByteBuffer buf) {
        System.out.println("result = " + result + " buf = " + buf);
        if (result > 0) {
            buf.flip();
            try {
                baos.write(buf.array()); 
            } catch (IOException e) {
                e.printStackTrace();
            }
            buf.clear();
            socket.read(buf, buf, this);
        } else if (result == -1) { //result為-1的時(shí)候，客戶端的socket已經(jīng)正常關(guān)閉。
            try {
                System.out.printf("客戶端%s已經(jīng)斷開.
", socket.getRemoteAddress().toString());
                String info = new String(baos.toByteArray(), Charset.forName("UTF8"));
                System.out.println(info);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                buf = null;
                try {
                    socket.close();
                } catch (IOException e) {}
            }
        }
    }

    public void failed(Throwable exc, ByteBuffer buf) {
        exc.printStackTrace();
    }
}

基本上，一個(gè)簡(jiǎn)單的AIOServer就上面這點(diǎn)代碼拉。實(shí)際上我感覺代碼比NIO用Selector的方式還是簡(jiǎn)單清晰多了。至于aio的原理，實(shí)際上就是去看看epoll等資料就知道了。

這里附上一個(gè)測(cè)試的客戶端代碼：

public class BioClient {
    public static void main(String[] args) throws Exception {
        String txt = "美國(guó)在發(fā)布的朝鮮軍力評(píng)估報(bào)告中也認(rèn)為：“朝鮮發(fā)展航天運(yùn)載工具對(duì)開發(fā)射程可達(dá)美國(guó)的遠(yuǎn)程導(dǎo)彈意義重要，射程也許能覆蓋美國(guó)部分地區(qū)。不過，由于朝鮮還沒有研發(fā)出能夠重返大氣層的運(yùn)載火箭，所以‘大浦洞2號(hào)’尚不具備搭載彈頭的攻擊能力。”";
        Socket socket = new Socket("localhost", 8080);
        PrintStream print = new PrintStream(socket.getOutputStream());
        print.print(txt);
        print.close();
        socket.close();
        System.out.println("ok.");
    }
}