NIO 使用的简单例子

1.FileChannel
fileChannel 是阻塞的,不可以运行在非阻塞模式,因此不能被注册到 Selector 上
简单例子如下:

File f = new File("abcd");        File f2 = new File("abcd2");        try (RandomAccessFile accessFile = new RandomAccessFile(f, "r");            RandomAccessFile accessFile2 = new RandomAccessFile(f2, "rw");            FileChannel fileChannel = accessFile.getChannel();            FileChannel fileChannel2 = accessFile2.getChannel();)        {            fileChannel2.position(fileChannel2.size());            ByteBuffer buffer = ByteBuffer.allocate(128);            while (fileChannel.read(buffer) > 0)            {                buffer.flip();                while (buffer.hasRemaining())                {                    fileChannel2.write(buffer);                }                buffer.clear();                System.out.println("------");            }        }

RandomAccessFile中获取FileChannel,通过ByteBuffer可以从FileChannel中读取数据也可以向FileChannel写入数据,注意写数据时需要使用 while 循环,因为不能保证 ByteBuffer 一次性将数据全部写入.fileChannel.force(true)方法强制将内存数据同步到磁盘(boolean 参数表示是否将文件元数据写入(权限信息等)).注意ByteBuffer读写之间需要调用方法flip,切换读写模式

2.使用 Selector
只有非阻塞的 channel 才能注册到 selector 上,因此必须使用非阻塞 channel,此处使用 socketChannel 与 socketServerChannel 来做示范,示例代码如下:

客户端代码:

public class SocketNio{    private static Charset charset = Charset.forName("UTF-8");    private static int IO_LENGTH = 20;    private static int BUFFER_SIZE = 128;    private static int PORT = 8090;    public static void main(String[] args)        throws IOException    {        SocketChannel channel = SocketChannel.open();        channel.connect(new InetSocketAddress(PORT));        ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);        @SuppressWarnings("resource")        Scanner input = new Scanner(System.in);        while (true)        {            String s = input.nextLine();            buffer.clear();            for (int i = 0; i < Math.ceil(s.length() / (double)IO_LENGTH); i++)            {                buffer.put(charset.encode(i * IO_LENGTH + IO_LENGTH > s.length() ? s.substring(i * IO_LENGTH)                    : s.substring(i * IO_LENGTH, i * IO_LENGTH + IO_LENGTH)));                buffer.flip();                while (buffer.hasRemaining())                {                    channel.write(buffer);                }                buffer.clear();            }        }    }}

客户端仅仅实现了一个发送数据的功能

服务端代码如下:

public class SocketServerNIO{    private static Charset charset = Charset.forName("UTF-8");    private static int PORT = 8090;    private static int BUFFER_SIZE = 128;    public static void main(String[] args)        throws IOException    {        ServerSocketChannel channel = ServerSocketChannel.open();        channel.bind(new InetSocketAddress(PORT));        channel.configureBlocking(false);        final Selector selector = Selector.open();        channel.register(selector, SelectionKey.OP_ACCEPT);        while (selector.select() > 0)        {            Set<SelectionKey> selectedKeys = selector.selectedKeys();            Iterator<SelectionKey> keyIterator = selectedKeys.iterator();            while (keyIterator.hasNext())            {                SelectionKey key = keyIterator.next();                if (key.isAcceptable())                {                    SocketChannel sc = ((ServerSocketChannel)key.channel()).accept();                    sc.configureBlocking(false);                    sc.register(selector, SelectionKey.OP_READ);                    // 将sk对应的Channel设置成准备接受其他请求                    key.interestOps(SelectionKey.OP_ACCEPT);                }                if (key.isReadable())                {                    // 获取该SelectionKey对应的Channel                    SocketChannel sc = (SocketChannel)key.channel();                    ByteBuffer buff = ByteBuffer.allocate(BUFFER_SIZE);                    String content = "";                    try                    {                        while (sc.read(buff) > 0)                        {                            buff.flip();                            content += charset.decode(buff);                            buff.clear();                        }                        System.out.println("读取的数据：" + content);                        key.interestOps(SelectionKey.OP_READ);                    }                    // 如果捕获到带sk对应的Channel出现了异常，即表明该Channel对应的Client出现了问题，                    // 所以从Selector中取消sk的注册                    catch (IOException e)                    {                        keyIterator.remove();                        key.cancel();                        if (key.channel() != null)                            key.channel().close();                    }                }                keyIterator.remove();            }        }    }}

服务端将 socketServerChannel 与每一个客户端连接的 socketChannel 均加入到 selector 监听,每当检测到有数据写入时,服务端就将写入数据打印出来,注意每个被注册的 channel 均被设置为非阻塞模式