java7 NIO2(8)The Asynchronous Channel API 异步通道API

异步channel API

主要引入三个异步类: AsynchronousFileChannel,AsynchronousSocketChannel, and AsynchronousServerSocketChannel.

AsynchronousFileChannel跟FileChannel区别：不保存全局的position和offset，可以制定访问位置，也支持并发访问文件不同。

AsynchronousServerSocketChannel AsynchronousSocketChannel：能够绑定到一个制定线程池的组中，这个线程池能够用future或者CompletionHandler来对执行结果进行处理，

AsynchronousChannelGroup：执行异步IO的java线程池的组类，

AsynchronousChannelGroup.java:

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

我们看使用示例

package com.mime;import java.io.IOException;import java.net.InetSocketAddress;import java.net.StandardSocketOptions;import java.nio.ByteBuffer;import java.nio.channels.AsynchronousChannelGroup;import java.nio.channels.AsynchronousFileChannel;import java.nio.channels.AsynchronousServerSocketChannel;import java.nio.channels.AsynchronousSocketChannel;import java.nio.channels.CompletionHandler;import java.nio.channels.FileLock;import java.nio.charset.Charset;import java.nio.file.Path;import java.nio.file.Paths;import java.nio.file.StandardOpenOption;import java.util.ArrayList;import java.util.List;import java.util.Set;import java.util.TreeSet;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;import java.util.concurrent.ThreadLocalRandom;public class NIO2AsynchronousFileChannel {public static void main(String[] args) {asyFile();asyFileChannel2();asyServerSocketChannel();}// 异步文件读写示例public static void asyFile() {ByteBuffer buffer = ByteBuffer.allocate(100);String encoding = System.getProperty("file.encoding");Path path = Paths.get("/tmp", "store.txt");try (AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ)) {Future<Integer> result = asynchronousFileChannel.read(buffer, 0);// 读超时控制// int count = result.get(100, TimeUnit.NANOSECONDS);while (!result.isDone()) {System.out.println("Do something else while reading ...");}System.out.println("Read done: " + result.isDone());System.out.println("Bytes read: " + result.get());// 使用CompletionHandler回调接口异步读取文件final Thread current = Thread.currentThread();asynchronousFileChannel.read(buffer, 0,"Read operation status ...",new CompletionHandler<Integer, Object>() {@Overridepublic void completed(Integer result, Object attachment) {System.out.println(attachment);System.out.print("Read bytes: " + result);current.interrupt();}@Overridepublic void failed(Throwable exc, Object attachment) {System.out.println(attachment);System.out.println("Error:" + exc);current.interrupt();}});} catch (Exception ex) {System.err.println(ex);}buffer.flip();System.out.print(Charset.forName(encoding).decode(buffer));buffer.clear();// 异步文件写示例ByteBuffer buffer1 = ByteBuffer.wrap("The win keeps Nadal at the top of the heap in men's".getBytes());Path path1 = Paths.get("/tmp", "store.txt");try (AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path1, StandardOpenOption.WRITE)) {Future<Integer> result = asynchronousFileChannel.write(buffer1, 100);while (!result.isDone()) {System.out.println("Do something else while writing ...");}System.out.println("Written done: " + result.isDone());System.out.println("Bytes written: " + result.get());// file lockFuture<FileLock> featureLock = asynchronousFileChannel.lock();System.out.println("Waiting for the file to be locked ...");FileLock lock = featureLock.get();if (lock.isValid()) {Future<Integer> featureWrite = asynchronousFileChannel.write(buffer, 0);System.out.println("Waiting for the bytes to be written ...");int written = featureWrite.get();// or, use shortcut// int written = asynchronousFileChannel.write(buffer,0).get();System.out.println("I’ve written " + written + " bytes into "+ path.getFileName() + " locked file!");lock.release();}// asynchronousFileChannel.lock("Lock operation status:", new// CompletionHandler<FileLock, Object>() ;} catch (Exception ex) {System.err.println(ex);}}// public static AsynchronousFileChannel open(Path file, Set<? extends// OpenOption> options,ExecutorService executor, FileAttribute<?>... attrs)// throws IOExceptionprivate static Set withOptions() {final Set options = new TreeSet<>();options.add(StandardOpenOption.READ);return options;}// 使用AsynchronousFileChannel.open(path, withOptions(),// taskExecutor))这个API对异步文件IO的处理public static void asyFileChannel2() {final int THREADS = 5;ExecutorService taskExecutor = Executors.newFixedThreadPool(THREADS);String encoding = System.getProperty("file.encoding");List<Future<ByteBuffer>> list = new ArrayList<>();int sheeps = 0;Path path = Paths.get("/tmp","store.txt");try (AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path, withOptions(), taskExecutor)) {for (int i = 0; i < 50; i++) {Callable<ByteBuffer> worker = new Callable<ByteBuffer>() {@Overridepublic ByteBuffer call() throws Exception {ByteBuffer buffer = ByteBuffer.allocateDirect(ThreadLocalRandom.current().nextInt(100, 200));asynchronousFileChannel.read(buffer, ThreadLocalRandom.current().nextInt(0, 100));return buffer;}};Future<ByteBuffer> future = taskExecutor.submit(worker);list.add(future);}// this will make the executor accept no new threads// and finish all existing threads in the queuetaskExecutor.shutdown();// wait until all threads are finishedwhile (!taskExecutor.isTerminated()) {// do something else while the buffers are preparedSystem.out.println("Counting sheep while filling up some buffers!So far I counted: "+ (sheeps += 1));}System.out.println("\nDone! Here are the buffers:\n");for (Future<ByteBuffer> future : list) {ByteBuffer buffer = future.get();System.out.println("\n\n" + buffer);System.out.println("______________________________________________________");buffer.flip();System.out.print(Charset.forName(encoding).decode(buffer));buffer.clear();}} catch (Exception ex) {System.err.println(ex);}}//异步server socket channel io处理示例public static void asyServerSocketChannel() {//使用threadGroup//AsynchronousChannelGroup threadGroup = null;//ExecutorService executorService = Executors//.newCachedThreadPool(Executors.defaultThreadFactory());//try {//threadGroup = AsynchronousChannelGroup.withCachedThreadPool(executorService, 1);//} catch (IOException ex) {//System.err.println(ex);//}//AsynchronousServerSocketChannel asynchronousServerSocketChannel =//AsynchronousServerSocketChannel.open(threadGroup);final int DEFAULT_PORT = 5555;final String IP = "127.0.0.1";ExecutorService taskExecutor = Executors.newCachedThreadPool(Executors.defaultThreadFactory());// create asynchronous server socket channel bound to the default grouptry (AsynchronousServerSocketChannel asynchronousServerSocketChannel = AsynchronousServerSocketChannel.open()) {if (asynchronousServerSocketChannel.isOpen()) {// set some optionsasynchronousServerSocketChannel.setOption(StandardSocketOptions.SO_RCVBUF, 4 * 1024);asynchronousServerSocketChannel.setOption(StandardSocketOptions.SO_REUSEADDR, true);// bind the server socket channel to local addressasynchronousServerSocketChannel.bind(new InetSocketAddress(IP,DEFAULT_PORT));// display a waiting message while ... waiting clientsSystem.out.println("Waiting for connections ...");while (true) {Future<AsynchronousSocketChannel> asynchronousSocketChannelFuture = asynchronousServerSocketChannel.accept();//使用CompletionHandler来处理IO事件//asynchronousServerSocketChannel.accept(null, new CompletionHandler<AsynchronousSocketChannel, Void>() //client使用CompletionHandler来处理IO事件//asynchronousSocketChannel.connect(new InetSocketAddress(IP, DEFAULT_PORT), null,new CompletionHandler<Void, Void>() try {final AsynchronousSocketChannel asynchronousSocketChannel = asynchronousSocketChannelFuture.get();Callable<String> worker = new Callable<String>() {@Overridepublic String call() throws Exception {String host = asynchronousSocketChannel.getRemoteAddress().toString();System.out.println("Incoming connection from: "+ host);final ByteBuffer buffer = ByteBuffer.allocateDirect(1024);// transmitting datawhile (asynchronousSocketChannel.read(buffer).get() != -1) {buffer.flip();}asynchronousSocketChannel.write(buffer).get();if (buffer.hasRemaining()) {buffer.compact();} else {buffer.clear();}asynchronousSocketChannel.close();System.out.println(host+ " was successfully served!");return host;}};taskExecutor.submit(worker);} catch (InterruptedException | ExecutionException ex) {System.err.println(ex);System.err.println("\n Server is shutting down ...");// this will make the executor accept no new threads// and finish all existing threads in the queuetaskExecutor.shutdown();// wait until all threads are finishedwhile (!taskExecutor.isTerminated()) {}break;}}} else {System.out.println("The asynchronous server-socket channel cannot be opened!");}} catch (IOException ex) {System.err.println(ex);}}}

输出：

Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Do something else while reading ...Read done: trueBytes read: 18hello,filechannelRead operation status ...Error:java.nio.channels.AsynchronousCloseExceptionDo something else while writing ...Do something else while writing ...Do something else while writing ...Written done: trueBytes written: 51Waiting for the file to be locked ...Waiting for the bytes to be written ...I’ve written 100 bytes into store.txt locked file!Counting sheep while filling up some buffers!So far I counted: 1Counting sheep while filling up some buffers!So far I counted: 2Counting sheep while filling up some buffers!So far I counted: 3Counting sheep while filling up some buffers!So far I counted: 4Counting sheep while filling up some buffers!So far I counted: 5Counting sheep while filling up some buffers!So far I counted: 6Counting sheep while filling up some buffers!So far I counted: 7Counting sheep while filling up some buffers!So far I counted: 8Counting sheep while filling up some buffers!So far I counted: 9Counting sheep while filling up some buffers!So far I counted: 10Counting sheep while filling up some buffers!So far I counted: 11Done! Here are the buffers:java.lang.InterruptedExceptionWaiting for connections ...