2.3Java 异步io式（AIO）

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本文深入解析Java异步IO（AIO）的工作原理，采用proactor模型，线程发起IO请求后立即返回，由操作系统完成IO操作并通知线程。通过服务器和客户端代码示例，展示了如何使用AsynchronousServerSocketChannel和AsynchronousSocketChannel实现非阻塞的网络通信。

Java 异步io式（AIO）

执行流程

AIO(proactor模型)：线程发起IO请求，立即返回；内存做好IO操作的准备之后，做IO操作，直到操作完成或者失败，通过调用注册的回调函数通知线程做IO操作完成或者失败。
异步非阻塞，服务器实现模式为一个有效请求一个线程，客户端的I/O请求都是由OS先完成了再通知服务器应用去启动线程进行处理，
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代码

1.server

public class Server {
    private static Charset charset = Charset.forName("utf-8");
    private static CharsetEncoder encoder = charset.newEncoder();

    public static void main(String[] args) throws Exception {
        AsynchronousChannelGroup group = AsynchronousChannelGroup.withThreadPool(Executors.newFixedThreadPool(4));
        AsynchronousServerSocketChannel server = AsynchronousServerSocketChannel.open(group).bind(new InetSocketAddress("0.0.0.0", 8013));
        server.accept(null, new CompletionHandler<AsynchronousSocketChannel, Void>() {
            @Override
            public void completed(AsynchronousSocketChannel result, Void attachment) {
                server.accept(null, this); // 接受下一个连接
                try {
                    String now = new Date().toString();
                    ByteBuffer buffer = encoder.encode(CharBuffer.wrap(now + "\r\n"));
                    //result.write(buffer, null, new CompletionHandler<Integer,Void>(){...}); //callback or
                    Future<Integer> f = result.write(buffer);
                    f.get();
                    System.out.println("sent to client: " + now);
                    result.close();
                } catch (IOException | InterruptedException | ExecutionException e) {
                    e.printStackTrace();
                }
            }
            @Override
            public void failed(Throwable exc, Void attachment) {
                exc.printStackTrace();
            }
        });
        group.awaitTermination(Long.MAX_VALUE, TimeUnit.SECONDS);
    }
}

2.client

public class Client {
    public static void main(String[] args) throws Exception {
        AsynchronousSocketChannel client = AsynchronousSocketChannel.open();
        Future<Void> future = client.connect(new InetSocketAddress("127.0.0.1", 8013));
        future.get();

        ByteBuffer buffer = ByteBuffer.allocate(100);
        client.read(buffer, null, new CompletionHandler<Integer, Void>() {
            @Override
            public void completed(Integer result, Void attachment) {
                System.out.println("client received: " + new String(buffer.array()));

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

            }
        });

        Thread.sleep(10000);
    }
}