java AIO示例

按照《Unix网络编程》的划分，IO模型可以分为：阻塞IO、非阻塞IO、IO复用、信号驱动IO和异步IO，按照POSIX标准来划分只分为两类：同步IO和异步IO。如何区分呢？首先一个IO操作其实分成了两个步骤：发起IO请求和实际的IO操作，同步IO和异步IO的区别就在于第二个步骤是否阻塞，如果实际的IO读写阻塞请求进程，那么就是同步IO，因此阻塞IO、非阻塞IO、IO服用、信号驱动IO都是同步IO，如果不阻塞，而是操作系统帮你做完IO操作再将结果返回给你，那么就是异步IO。阻塞IO和非阻塞IO的区别在于第一步，发起IO请求是否会被阻塞，如果阻塞直到完成那么就是传统的阻塞IO，如果不阻塞，那么就是非阻塞IO。

   Java nio 2.0的主要改进就是引入了异步IO（包括文件和网络），这里主要介绍下异步网络IO API的使用以及框架的设计，以TCP服务端为例。首先看下为了支持AIO引入的新的类和接口：

 java.nio.channels.AsynchronousChannel
       标记一个channel支持异步IO操作。

 java.nio.channels.AsynchronousServerSocketChannel
       ServerSocket的aio版本，创建TCP服务端，绑定地址，监听端口等。

 java.nio.channels.AsynchronousSocketChannel
       面向流的异步socket channel，表示一个连接。

 java.nio.channels.AsynchronousChannelGroup
       异步channel的分组管理，目的是为了资源共享。一个AsynchronousChannelGroup绑定一个线程池，这个线程池执行两个任务：处理IO事件和派发CompletionHandler。AsynchronousServerSocketChannel创建的时候可以传入一个 AsynchronousChannelGroup，那么通过AsynchronousServerSocketChannel创建的 AsynchronousSocketChannel将同属于一个组，共享资源。

 java.nio.channels.CompletionHandler

       异步IO操作结果的回调接口，用于定义在IO操作完成后所作的回调工作。AIO的API允许两种方式来处理异步操作的结果：返回的Future模式或者注册CompletionHandler，我更推荐用CompletionHandler的方式，这些handler的调用是由 AsynchronousChannelGroup的线程池派发的。显然，线程池的大小是性能的关键因素。AsynchronousChannelGroup允许绑定不同的线程池，通过三个静态方法来创建：

public static AsynchronousChannelGroup withFixedThreadPool(int nThreads,                                                                 ThreadFactory threadFactory)          throws IOException     public static AsynchronousChannelGroup withCachedThreadPool(ExecutorService executor,                                                                  int initialSize)     public static AsynchronousChannelGroup withThreadPool(ExecutorService executor)          throws IOException  

需要根据具体应用相应调整，从框架角度出发，需要暴露这样的配置选项给用户。

     在介绍完了aio引入的TCP的主要接口和类之后，我们来设想下一个aio框架应该怎么设计。参考非阻塞nio框架的设计，一般都是采用Reactor模式，Reacot负责事件的注册、select、事件的派发；相应地，异步IO有个Proactor模式，Proactor负责 CompletionHandler的派发，查看一个典型的IO写操作的流程来看两者的区别：

     Reactor:  send(msg) -> 消息队列是否为空，如果为空  -> 向Reactor注册OP_WRITE，然后返回 -> Reactor select -> 触发Writable，通知用户线程去处理 ->先注销Writable(很多人遇到的cpu 100%的问题就在于没有注销）,处理Writeable，如果没有完全写入，继续注册OP_WRITE。注意到，写入的工作还是用户线程在处理。
     Proactor: send(msg) -> 消息队列是否为空，如果为空,发起read异步调用，并注册CompletionHandler，然后返回。 -> 操作系统负责将你的消息写入，并返回结果（写入的字节数）给Proactor -> Proactor派发CompletionHandler。可见，写入的工作是操作系统在处理，无需用户线程参与。事实上在aio的API 中,AsynchronousChannelGroup就扮演了Proactor的角色。

    CompletionHandler有三个方法，分别对应于处理成功、失败、被取消（通过返回的Future)情况下的回调处理：

public interface CompletionHandler<V,A> {          void completed(V result, A attachment);         void failed(Throwable exc, A attachment);               void cancelled(A attachment);   }  

其中的泛型参数V表示IO调用的结果，而A是发起调用时传入的attchment。

 第一步，创建一个AsynchronousServerSocketChannel，创建之前先创建一个 AsynchronousChannelGroup，上文提到AsynchronousServerSocketChannel可以绑定一个 AsynchronousChannelGroup，那么通过这个AsynchronousServerSocketChannel建立的连接都将同属于一个AsynchronousChannelGroup并共享资源：

this.asynchronousChannelGroup = AsynchronousChannelGroup                       .withCachedThreadPool(Executors.newCachedThreadPool(),                               this.threadPoolSize);  

然后初始化一个AsynchronousServerSocketChannel，通过open方法：

this.serverSocketChannel = AsynchronousServerSocketChannel                   .open(this.asynchronousChannelGroup);  

通过nio 2.0引入的SocketOption类设置一些TCP选项：

this.serverSocketChannel                       .setOption(                               StandardSocketOption.SO_REUSEADDR,true);   this.serverSocketChannel                       .setOption(                               StandardSocketOption.SO_RCVBUF,16*1024);  

    绑定本地地址：

this.serverSocketChannel                       .bind(new InetSocketAddress("localhost",8080), 100);  

完整示例

package com.longshine.nio.aio;import java.io.IOException;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.channels.AsynchronousServerSocketChannel;import java.nio.channels.AsynchronousSocketChannel;import java.util.concurrent.ExecutionException;import java.util.concurrent.Future;public class Server {AsynchronousServerSocketChannel server;public void init(){try {server = AsynchronousServerSocketChannel.open();server.bind(new InetSocketAddress(8000));System.out.println("服务器启动");Future future = server.accept();AsynchronousSocketChannel client = (AsynchronousSocketChannel)future.get();System.out.println("有客户连接");ByteBuffer buffer = ByteBuffer.allocate(1000);client.read(buffer).get();byte []arr = readBuffer(buffer);System.out.println(new String(arr));} catch (IOException e) {e.printStackTrace();}catch(Exception e){e.printStackTrace();}}public static byte[] readBuffer(ByteBuffer buffer){buffer.flip();int len = buffer.limit() - buffer.position();byte[] ret = new byte[len];System.arraycopy(buffer.array(), 0, ret, 0, len);return ret;}public static void main(String[] args) throws Exception{new Thread(){public void run(){new Server().init();}}.start();Thread.sleep(2000);new Thread(){public void run(){new Client().init();}}.start();}}class Client{public void init(){try {AsynchronousSocketChannel channel = AsynchronousSocketChannel.open();channel.connect(new InetSocketAddress("127.0.0.1",8000)).get();System.out.println("连接服务器成功");ByteBuffer buffer = ByteBuffer.allocate(1000);buffer.put("aaaaaaaaaaaaaa".getBytes());buffer.flip();channel.write(buffer).get();System.out.println("写数据成功");} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}catch (IOException e) {e.printStackTrace();}}}

CompletedHandler示例

package com.longshine.nio.aio;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.ExecutionException;public class Server2 {public void init(){try{final AsynchronousServerSocketChannel channel = AsynchronousServerSocketChannel.open();channel.bind(new InetSocketAddress(8000));System.out.println("服务器启动");channel.accept(null, new CompletionHandler<AsynchronousSocketChannel,Object>(){public void completed(AsynchronousSocketChannel result, Object attachment) {try{System.out.println("客户连接");new Thread(new ClientHandler(result)).start();}catch(Exception e){}finally{channel.accept(null, this);}}public void failed(Throwable exc, Object attachment) {System.out.println("失败");}});while(true){System.out.println("我在做自己的事情");Thread.sleep(1000);}}catch(Exception e){}}public static void main(String[] args) throws Exception{new Thread(){public void run(){new Server2().init();}}.start();for(int i = 0; i< 10; i++){new Thread(){public void run(){new Client2().init();}}.start();Thread.sleep(1000);}}public static byte[] readBuffer(ByteBuffer buffer){buffer.flip();int len = buffer.limit() - buffer.position();byte[] ret = new byte[len];System.arraycopy(buffer.array(), 0, ret, 0, len);return ret;}}class Client2{public void init(){try {AsynchronousSocketChannel channel = AsynchronousSocketChannel.open();channel.connect(new InetSocketAddress("127.0.0.1",8000)).get();System.out.println("连接服务器成功");ByteBuffer buffer = ByteBuffer.allocate(1000);channel.read(buffer).get();System.out.println("服务器说:"+new String(Server2.readBuffer(buffer)));} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}catch (IOException e) {e.printStackTrace();}}}

package com.longshine.nio.aio;import java.nio.ByteBuffer;import java.nio.channels.AsynchronousSocketChannel;import java.util.concurrent.ExecutionException;public class ClientHandler implements Runnable{private AsynchronousSocketChannel channel;public ClientHandler(AsynchronousSocketChannel channel){this.channel = channel;}public void run(){ByteBuffer buffer = ByteBuffer.allocate(1000);buffer.put("hello".getBytes());buffer.flip();try {channel.write(buffer).get();} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}}}