图解IO模型——BIO，NIO，AIO
服务架构模式——TPC/PPC模式
服务架构模式——单Reactor模式
服务架构模式——多Reactor模式
服务架构模式——Proactor模式

Proactor模式基于AIO，应用程序向内核注册一个Proactor和Handler，将所有I/O操作都交给内核来处理，内核完成数据读写后回调Handler完成业务处理。

Proactor模式

内核和应用程序交互分为“向内核注册”和“请求处理”两个过程，如下图所示。

proactor.jpg

向内核注册Proactor和Handler

1. Proactor initiator创建Proactor
2. Proactor initiator创建Handler
3. Proactor通过内核提供的Asynchronous Operation processor把Proactor和Handle注册到内核

内核读取数据完成后回调handler

4. 当IO操作完成时，内核通知Proactor
5. Proactor根据不同的IO事件回调不同的Handler完成业务处理

Proactor代码实现

服务端初始化AsynchronousServerSocketChannel ，向内核注册连接事件由AIOAcceptHandler处理

public class AIOServer implements Runnable{
   ......
        @Override
    public void run() {
        //打开异步ServerSocketChannel，绑定端口
        try (AsynchronousServerSocketChannel serverSocketChannel = AsynchronousServerSocketChannel.open()){
            serverSocketChannel.bind(new InetSocketAddress(InetAddress.getLocalHost(), Constant.port));
            System.out.println("AIO server started at port " + Constant.port);
            
            //注册Accept事件由AIOAcceptHandler处理
            serverSocketChannel.accept(serverSocketChannel, new AIOAcceptHandler());
            serverStatus.await();
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }

}

AIOAcceptHandler继承CompletionHandler，当连接事件完成后内核会回调这个类 completed方法，连接失败时回调 failed方法。 在completed方法中，应用程序向内核注册“读事件”的处理类为ReadCompletionHanlder。

public class AIOAcceptHandler implements CompletionHandler<AsynchronousSocketChannel, AsynchronousServerSocketChannel> {
    @Override
    public void completed(AsynchronousSocketChannel channel, AsynchronousServerSocketChannel attachment) {
        //异步处理下一个连接
        attachment.accept(attachment, this);

        //处理本连接
        Buffers buffers = new Buffers();
        channel.read(buffers.getReadBuff(), buffers, new ReadCompletionHanlder(channel));
    }

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

ReadCompletionHanlder也继承CompletionHandler，当IO读操作完成时，内核回调这个类

public class ReadCompletionHanlder implements CompletionHandler<Integer, Buffers> {
   ......
    //数据读取完成时，回调此方法
    @Override
    public void completed(Integer result, Buffers buff) {
        //读取请求
        ByteBuffer readBuff = buff.getReadBuff();
        readBuff.flip();
        CharBuffer cBuff = utf8.decode(readBuff);
        String request = cBuff.toString();
        System.out.println("Received request: " + request);

        //构建响应
        ByteBuffer writeBuff = buff.getWriteBuff();
        writeBuff.put(("Hello " + request).getBytes());
        writeBuff.flip();
    }

    //数据读取失败时，回调此方法
    @Override
    public void failed(Throwable exc, Buffers attachment) {
        exc.printStackTrace();
    }
}