NIO2.0 AIO入门

左手的ㄟ右手 2021-11-16 13:10 293阅读 0赞

NIO 2.0引入了新的异步通道的概念，并提供了异步文件通道和异步套接字通道的实现。异步通道提供一下两种方式获取操作结果。

1.  通过java.util.concurrent.Future类来表示异步操作的结果；
2.  在执行异步操作的时候传入一个java.nio.channels。  
    CompletionHandler接口的实现类作为操作完成的回调

NIO 2.0的异步套接字通道是真正的异步非阻塞I/O，对应于UNIX网络编程中的事件驱动I/O(AIO)。它不需要通过多路复用器(Selector)对注册的通道进行轮询操作即可实现异步读写，从而简化了NIO的编程模型。

简单的说，NIO1.0 和NIO2.0 相比最大的区别是NIO1.0通过多路复用器轮询来获取读写事件，然后执行具体的操作，NIO2.0采用和Future和回调，使用上更加简洁。

下面是一个例子，客户端向服务端发一个时间查询消息，服务端返回查询的结果。  
eg  
服务端：

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 {
                //创建一个服务端通道
                asynchronousServerSocketChannel = AsynchronousServerSocketChannel.open();
                //绑定监听端口
                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);
            //接收客户端请求
            doAccept();
            try {
                latch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        public void doAccept() {
            //注册接收客户端请求，接收到请求会回调acceptCompletionHandler类
            asynchronousServerSocketChannel.accept(this, new AcceptCompletionHandler());
        }
    }

public class AcceptCompletionHandler implements CompletionHandler<AsynchronousSocketChannel, AsyncTimeServerHandler> {
        @Override
        public void completed(AsynchronousSocketChannel result, AsyncTimeServerHandler attachment) {
            //接收到客户端请求后，在注册接收请求，用于接收其他客户端的请求
            attachment.asynchronousServerSocketChannel.accept(attachment, this);
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            //监听该客户端连接上的读请求，如果接收到消息，会调用readCompletionHandler
            result.read(buffer, buffer, new ReadCompletionHandler(result));
        }
    
        @Override
        public void failed(Throwable exc, AsyncTimeServerHandler attachment) {
            //接收失败的回调
            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) {
            //读取客户端请求
            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";
                //回复客户端消息
                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();
                //向客户端回复消息
                channel.write(writeBuffer, writeBuffer,
                        new CompletionHandler<Integer, ByteBuffer>() {
                            @Override
                            public void completed(Integer result, ByteBuffer attachment) {
                                // 如果没有发送完成，继续发送
                                if(attachment.hasRemaining()){
                                    channel.write(attachment,attachment,this);
                                }
                            }
    
                            @Override
                            public void failed(Throwable exc, ByteBuffer attachment) {
                                try {
                                    channel.close();
                                } catch (IOException e) {
                                    e.printStackTrace();
                                }
                            }
                        });
            }
        }
    }

客户端:

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 {
                //创建一个连接通道
                client = AsynchronousSocketChannel.open();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    
        @Override
        public void run() {
            latch = new CountDownLatch(1);
            //异步连接服务端，连接成功回调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) {
            //连接成功发送消息
            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);
                                //发送完消息，监听读消息
                                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();
            }
        }
    }