NIO2.0

最新推荐文章于 2025-01-24 19:17:37 发布

zero__007

最新推荐文章于 2025-01-24 19:17:37 发布

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分类专栏： # 【NIO】

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本文介绍Java NIO2.0中新增的异步文件I/O操作及与UNIX网络编程事件驱动I/O对应的AIO。通过示例代码展示了如何使用AsynchronousServerSocketChannel和AsynchronousSocketChannel实现服务器和客户端的异步通信。

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JDK1.7升级了NIO类库，升级后的NIO类库被称为NIO2.0，引人注目的是，Java正式提供了异步文件I/O操作，同时提供了与UNIX网络编程事件驱动I/O对应的AIO。
NIO2.0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。异步通道提供两种方式获取操作结果。

通过java.util.concurrent.Future类来表示异步操作的结果；
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。

NIO2.0的异步套接字通道是真正的异步非阻塞I/O，它对应UXIN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。

示例：
AIOServer.java

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousChannel;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.CountDownLatch;

public class AIOServer implements  Runnable{
    private CountDownLatch latch;
    private AsynchronousServerSocketChannel asySSC;
    
    public AIOServer(){
        try {
            asySSC = AsynchronousServerSocketChannel.open();
            asySSC.bind(new InetSocketAddress(9100));
            System.out.println("Server is start...");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        new Thread(new AIOServer()).start();
    }

    @Override
    public void run() {
        latch = new CountDownLatch(1);
        asySSC.accept(this, new AcceptCompletionHandler());
        System.out.println("Server accept()");
        try {
            System.out.println("Server latch.await()");
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    
    private class AcceptCompletionHandler implements CompletionHandler<AsynchronousSocketChannel, AIOServer>{
        @Override
        public void completed(AsynchronousSocketChannel result, AIOServer attachment) {
            System.out.println("AcceptCompletionHandler completed()");
           //既然已经接收到了客户端，为什么还要再次调用accept()?
            //原因：调用accept()方法后，如果有新的客户端连接接入，系统将回调传入的CompletionHandler实例的completed()方法，
            //表示新的客户端连接接入，AsynchronousServerSocketChannel可以接受成千上万个客户端
            attachment.asySSC.accept(attachment,this);
            
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            //read是异步的，
            //ByteBuffer dst: 接收缓冲区，用于从异步Channel中读取数据包
            //A attachment：异步Channe携带的附件，通知回调的时候作为入参使用
            //CompletionHandler<Integer,? super A> handler：接收通知回调的业务handler
            result.read(buffer,buffer,new ReadCompletionHandler(result));
        }

        @Override
        public void failed(Throwable exc, AIOServer attachment) {
            System.out.println("AcceptCompletionHandler failed()");
            exc.printStackTrace();
            attachment.latch.countDown();
        }
    }
    
    //主要用于读取半包消息和发送应答
    private class ReadCompletionHandler implements CompletionHandler<Integer, ByteBuffer>{
       private AsynchronousSocketChannel channel;
        public ReadCompletionHandler(AsynchronousSocketChannel channel){
            if (this.channel == null){
                this.channel = channel;
            }
        }
        
        @Override
        public void completed(Integer result, ByteBuffer attachment) {
            System.out.println("ReadCompletionHandler completed()");
            attachment.flip();
            byte[] body = new byte[attachment.remaining()];
            attachment.get(body);
            String req = new String(body, StandardCharsets.UTF_8);
            System.out.println("Server receive :" + req);
            doWrite("Server ack.");
        }

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

        private void doWrite(String msg) {
            byte[] bytes = msg.getBytes();
            ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
            writeBuffer.put(bytes);//将字节数组复制到缓冲区
            writeBuffer.flip();
          
            //异步write
            channel.write(writeBuffer, writeBuffer, new CompletionHandler<Integer, ByteBuffer>() {
                @Override
                public void completed(Integer result, ByteBuffer attachment) {
                    //如果没有完成发送，继续发送
                    if(attachment.hasRemaining()){
                        channel.write(attachment,attachment,this);
                    }
                }

                @Override
                public void failed(Throwable exc, ByteBuffer attachment) {
                    try {
                        channel.close();//关闭链路，释放资源
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            });
        }          
    }
}

AIOClient.java

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.CountDownLatch;

public class AIOClient implements CompletionHandler<Void, AIOClient>, Runnable {
    private AsynchronousSocketChannel clientChannel;
    private CountDownLatch latch;

    public AIOClient() {
        try {
            clientChannel = AsynchronousSocketChannel.open();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        new Thread(new AIOClient()).start();
    }

    @Override
    public void run() {
        latch = new CountDownLatch(1);

        //SocketAddress remote：服务器信息
        //A attachment: AsynchronousSocketChannel的附件，通知回调的时候作为入参使用
        //CompletionHandler<Void,? super A> handler: 异步操作回调通知接口
        clientChannel.connect(new InetSocketAddress("127.0.0.1", 9100), this, this);
        try {
            latch.await();//防止异步操作没有执行完成线程就退出
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        try {
            clientChannel.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void completed(Void result, AIOClient attachment) {
        System.out.println("Client completed()");
        byte[] req = "Client ...".getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
        writeBuffer.put(req);
        writeBuffer.flip();
        clientChannel.write(writeBuffer, writeBuffer, new CompletionHandler<Integer, ByteBuffer>() {
            @Override
            public void completed(Integer result, ByteBuffer attachment) {
                if (attachment.hasRemaining()) {
                    clientChannel.write(writeBuffer, writeBuffer, this);
                } else {
                    ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                    clientChannel.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 = new String(bytes, StandardCharsets.UTF_8);
                            System.out.println("Client receive : " + body);
                            latch.countDown();
                        }

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

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

    @Override
    public void failed(Throwable exc, AIOClient attachment) {
        System.out.println("Client failed()");
        try {
            clientChannel.close();
            latch.countDown();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

运行结果：
Server：

Server is start...
Server accept()
Server latch.await()
AcceptCompletionHandler completed()
ReadCompletionHandler completed()
Server receive :Client ...

Client：

Client completed()
Client receive : Server ack.