Java粗浅认识-I/O（四）

AIO

什么是AIO，既是异步IO，这里的异步对照io第一篇里面异步IO流程图，在请求数据和回传数据两个阶段都是交给操作系统内核态异步处理，无需用户态阻塞等待，Java1.7中新增处理异步IO的类，AsynchronousFileChannel、AsynchronousServerSocketChannel、AsynchronousSocketChannel、AsynchronousChannelGroup（线程池管理），这里需要注意一点，异步IO只在Windows上真正实现。

1.AIO，文件读取

    private static void readFile() throws IOException, InterruptedException, ExecutionException {
        Path path = Paths.get(\"C:\\\\Users\\\\baopz\\\\Desktop\\\\图片\\\\test\\\\1.txt\");
        AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
        //16k
        ByteBuffer buffer = ByteBuffer.allocateDirect(1 << 14);
        Future<Integer> future = asynchronousFileChannel.read(buffer, 0);
        System.out.println(future.get());
        asynchronousFileChannel.close();
    }

2.AIO，带CompletionHandler处理

这里使用了CompletionHandler的回调处理机制，在任务处理完毕后，Handler会自行根据传入的数据以及实现的逻辑进行结果处理，包括异常处理。

   public static void readFileWithCompletedHandler() throws IOException, InterruptedException {
        Path path = Paths.get(\"C:\\\\Users\\\\baopz\\\\Desktop\\\\图片\\\\test\\\\1.gif\");
        AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
        //16k
        ByteBuffer buffer = ByteBuffer.allocateDirect(1 << 14);
        asynchronousFileChannel.read(buffer, 0, null, new CompletionHandler<Integer,  >() {
            @Override
            public void completed(Integer result,   attachment) {
                System.out.println(\"读取文件已经完成,读取长度\" + result);
            }

            @Override
            public void failed(Throwable exc,   attachment) {
                System.out.println(\"读取文件错误\");
            }
        });
        asynchronousFileChannel.close();
    }

3.AIO，文件拷贝

  /**
     * 异步文件拷贝
     * @throws IOException
     */
    public static void copyFile() throws IOException {
        Path path = Paths.get(\"C:\\\\Users\\\\baopz\\\\Desktop\\\\图片\\\\test\\\\1.gif\");
        Path target = Paths.get(\"C:\\\\Users\\\\baopz\\\\Desktop\\\\图片\\\\test\\\\2.gif\");
        if (Files.notExists(target)) {
            Files.createFile(target);
        }
        ExecutorService executorService = Executors.newCachedThreadPool();
        AsynchronousFileChannel readChannel = AsynchronousFileChannel.open(path, Collections.singleton(StandardOpenOption.READ),executorService );
        AsynchronousFileChannel writeChannel = AsynchronousFileChannel.open(target, StandardOpenOption.WRITE);
        //16k
        final ByteBuffer buffer = ByteBuffer.allocateDirect(1 << 14);
        readChannel.read(buffer, 0, writeChannel, new CompletionHandler<Integer, AsynchronousFileChannel>() {
            @Override
            public void completed(Integer result, AsynchronousFileChannel attachment) {
                buffer.flip();
                Future<Integer> future = attachment.write(buffer, 0);
                try {
                    System.out.println(future.get());
                    attachment.close();
                } catch (IOException | InterruptedException | ExecutionException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void failed(Throwable exc, AsynchronousFileChannel attachment) {
                System.out.println(\"异常情况\" + exc.toString());
                try {
                    attachment.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
        if(readChannel.isOpen()) {
            readChannel.close();
        }
        executorService.shutdown();
    }

4.AIO文件网络通信拷贝

1.server端

private static void server() throws IOException, InterruptedException, ExecutionException {
        AsynchronousChannelGroup group = AsynchronousChannelGroup.withCachedThreadPool(Executors.newCachedThreadPool(), 5);
        AsynchronousServerSocketChannel serverSocketChannel = AsynchronousServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(8888));
        System.out.println(\"绑定成功。\");
        Future<AsynchronousSocketChannel> future = serverSocketChannel.accept();
        //阻塞接收连接
        AsynchronousSocketChannel asynchronousSocketChannel =  future.get();

        //16k
        ByteBuffer byteBuffer = ByteBuffer.allocateDirect(1 << 14);
        asynchronousSocketChannel.read(byteBuffer);
        Path path = Paths.get(\"C:\\\\Users\\\\baopz\\\\Desktop\\\\图片\\\\test\\\\4.gif\");
        if (Files.notExists(path)) {
            try {
                Files.createFile(path);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            ExecutorService executorService1 = Executors.newCachedThreadPool();
            AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path, Collections.singleton(StandardOpenOption.WRITE), executorService1);
            byteBuffer.flip();
            while (!asynchronousFileChannel.write(byteBuffer, 0).isDone()) {
                TimeUnit.MILLISECONDS.sleep(500);
            }
            asynchronousFileChannel.close();
            executorService1.shutdown();
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }

        serverSocketChannel.close();
        if (!group.isShutdown()) {
            group.shutdown();
        }
    }

2.客户端

private static void client() throws IOException, InterruptedException, ExecutionException {
        AsynchronousSocketChannel asynchronousSocketChannel = AsynchronousSocketChannel.open();
        Future<Void> voidFuture = asynchronousSocketChannel.connect(new InetSocketAddress(\"127.0.0.1\", 8888));
        //阻塞等待连接
        voidFuture.get();
        System.out.println(\"连接成功\");
        Path path = Paths.get(\"C:\\\\Users\\\\baopz\\\\Desktop\\\\图片\\\\test\\\\1.gif\");
        //16k
        final ByteBuffer buffer = ByteBuffer.allocateDirect(1 << 14);
        AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
        Future<Integer> integerFuture = asynchronousFileChannel.read(buffer, 0);
        int result = integerFuture.get();
        System.out.println(result);
        buffer.flip();
        Future<Integer> integerFuture1 = asynchronousSocketChannel.write(buffer);
        try {
            System.out.println(\"写出去数据：\" + integerFuture1.get());
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        asynchronousSocketChannel.close();
    }

总结，到这里Java I/O相关操作，介绍完毕，从Java 1.0开始的InputStrem和OutputStream，在Java 4中出现的Buffer、Channel、Selector，在Java 7出现的Path、Files、FilesSystems、AsynchronousFileChannel、AsynchronousServerSocketChannel等等都介绍完毕了，下一篇，记录Java中网络通信