AIO及基础实现

AIO：异步非阻塞IO，当系统中有IO操作后，会产生一个单独的线程，由它将所有需要处理的事情交由本地操作系统来完成，操作系统处理完成后，再将结果返回即可。

以常用的烧水问题来举例，服务器让A去烧水，A在水壶上装了一个开关，这个开关当水烧开时会通知A水已经烧好，再由A来处理，这个开关主要就是通过回调函数来实现。

在AIO中，主要通过使用CompletionHandler来完成，CompletionHandler是用于消除异步I / O操作结果的处理程序。

CompletionHandler有两个接口方法completed与failed

```
void completed(V result,
               A attachment)
```
操作完成后调用。

参数

result - I / O操作的结果。

attachment - 启动时附加到I / O操作的对象。

```
void failed(Throwable exc,
            A attachment)
```
当操作失败时调用。

参数

exc - 表示I / O操作失败的原因的例外

attachment - 启动时附加到I / O操作的对象。

以下是学习过程中找的AIO相关实现代码，在此做个记录：

服务端：

package com.learn.aio.server;

import com.study.info.HostInfo;

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

class EchoHandler implements CompletionHandler<Integer, ByteBuffer> {

    private AsynchronousSocketChannel clientChannel;
    private boolean exit;

    public EchoHandler(AsynchronousSocketChannel clientChannel) {
        this.clientChannel = clientChannel;
    }

    @Override
    public void completed(Integer result, ByteBuffer byteBuffer) {
        byteBuffer.flip();  // 读取之前先重置
        String read = new String(byteBuffer.array(), 0, byteBuffer.remaining()).trim();
        String outMsg = "【Echo】" + read;    // 回应的信息
        if ("byebye".equalsIgnoreCase(read)) {
            outMsg = "服务已断开，拜拜";
            this.exit = true;
        }
        this.echoWrite(outMsg);
    }

    private void echoWrite(String content){
        ByteBuffer buffer = ByteBuffer.allocate(100);
        buffer.put(content.getBytes());
        buffer.flip();
        this.clientChannel.write(buffer,buffer,new CompletionHandler<Integer,ByteBuffer>(){

            @Override
            public void completed(Integer result, ByteBuffer buf) {
                if (buf.hasRemaining()){
                    EchoHandler.this.clientChannel.write(buffer, buffer, this);
                }else {
                    if(EchoHandler.this.exit == false){
                        ByteBuffer readBuffer = ByteBuffer.allocate(100);
                        EchoHandler.this.clientChannel.read(readBuffer, readBuffer, new EchoHandler(EchoHandler.this.clientChannel));
                    }
                }
            }

            @Override
            public void failed(Throwable exc, ByteBuffer buf) {
                try {
                    EchoHandler.this.clientChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
    }

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

// 连接接收的回调处理
class AcceptHandler implements CompletionHandler<AsynchronousSocketChannel, AIOServerThread> {

    @Override
    public void completed(AsynchronousSocketChannel channel, AIOServerThread aioServerThread) {
        aioServerThread.getServerChannel().accept(aioServerThread, this);   // 接收连接
        ByteBuffer byteBuffer = ByteBuffer.allocate(100);
        channel.read(byteBuffer, byteBuffer, new EchoHandler(channel));
    }

    @Override
    public void failed(Throwable exc, AIOServerThread aioServerThread) {
        System.out.println("客户端连接创建失败....");
        aioServerThread.getLatch().countDown();
    }
}

//设置服务器处理线程
class AIOServerThread implements Runnable {

    private AsynchronousServerSocketChannel serverChannel = null;   //服务器通道
    private CountDownLatch latch = null;    //同步处理操作层

    public AIOServerThread() throws Exception {
        this.latch = new CountDownLatch(1);
        this.serverChannel = AsynchronousServerSocketChannel.open();    //打开服务器通道
        this.serverChannel.bind(new InetSocketAddress(HostInfo.PORT));
        System.out.println("服务已启动，监听端口为：" + HostInfo.PORT);
    }

    public AsynchronousServerSocketChannel getServerChannel() {
        return serverChannel;
    }

    public CountDownLatch getLatch() {
        return latch;
    }

    @Override
    public void run() {
        this.serverChannel.accept(this, new AcceptHandler());
        try {
            this.wait();    // 线程等待
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class AIOEchoServer {
    public static void main(String[] args) throws Exception{
        new Thread(new AIOServerThread()).start();
    }
}

客户端：

package com.learn.aio.client;

import com.study.info.HostInfo;
import com.study.util.InputUtil;

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

class ClientReadHandler implements CompletionHandler<Integer, ByteBuffer>{
    private AsynchronousSocketChannel clientChannel;
    private CountDownLatch latch;

    public ClientReadHandler(AsynchronousSocketChannel clientChannel, CountDownLatch latch) {
        this.clientChannel = clientChannel;
        this.latch = latch;
    }

    @Override
    public void completed(Integer result, ByteBuffer buffer) {
        buffer.flip();
        String readMsg = new String(buffer.array(), 0, buffer.remaining());
        System.out.println(readMsg);
    }

    @Override
    public void failed(Throwable exc, ByteBuffer attachment) {
        try {
            this.clientChannel.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        this.latch.countDown();
    }
}
class ClientWriteHandler implements CompletionHandler<Integer, ByteBuffer>{
    private AsynchronousSocketChannel clientChannel;
    private CountDownLatch latch;

    public ClientWriteHandler(AsynchronousSocketChannel clientChannel, CountDownLatch latch) {
        this.clientChannel = clientChannel;
        this.latch = latch;
    }

    @Override
    public void completed(Integer result, ByteBuffer buffer) {
        if(buffer.hasRemaining()){
            this.clientChannel.write(buffer, buffer, this);
        }else {
            ByteBuffer readBuffer = ByteBuffer.allocate(100);
            this.clientChannel.read(readBuffer, readBuffer, new ClientReadHandler(this.clientChannel, this.latch));
        }
    }

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

class AIOClientThread implements Runnable {

    private AsynchronousSocketChannel clientChannel;
    private CountDownLatch latch;

    public AIOClientThread() throws Exception{
        this.clientChannel = AsynchronousSocketChannel.open();
        this.clientChannel.connect(new InetSocketAddress(HostInfo.HOST_NAME, HostInfo.PORT));
        this.latch = new CountDownLatch(1);
    }

    @Override
    public void run() {
        try {
            this.latch.wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public boolean sendMessage(String msg){
        ByteBuffer byteBuffer = ByteBuffer.allocate(100);
        byteBuffer.put(msg.getBytes());
        byteBuffer.flip();
        this.clientChannel.write(byteBuffer, byteBuffer, new ClientWriteHandler(this.clientChannel, this.latch));
        if("byebye".equalsIgnoreCase(msg)){
            return false;
        }
        return  true;
    }
}

public class AIOEchoClient {
    public static void main(String[] args) throws Exception{
        AIOClientThread clientThread = new AIOClientThread();
        new Thread(clientThread).start();
        while (clientThread.sendMessage(InputUtil.getString("请输入要发送的内容："))){

        }
    }
}

其他：

package com.study.util;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputUtil {
    private static final BufferedReader KEYBOARD_INPUT = new BufferedReader(new InputStreamReader(System.in));

    private InputUtil(){
    }

    public static String getString(String prompt){
        boolean flag = true;    //数据接受标记
        String str = null;
        while (flag){
            System.out.println(prompt);
            try {
                str = KEYBOARD_INPUT.readLine();    // 读取一行数据
                if(str == null || "".equals(str)){
                    System.out.println("数据输入错误，不允许为空！");
                }else {
                    flag = false;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return str;
    }
}

package com.study.info;

public interface HostInfo {
    public static final String HOST_NAME = "localhost";
    public static final int PORT = 9999;
}

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