NIO Socket非阻塞模式

NIO主要原理和适用

NIO 有一个主要的类Selector,这个类似一个观察者，只要我们把需要探知的socketchannel告诉Selector,我们接着做别的事情，当有 事件发生时，他会通知我们，传回一组SelectionKey,我们读取这些Key,就会获得我们刚刚注册过的socketchannel,然后，我们从 这个Channel中读取数据，放心，包准能够读到，接着我们可以处理这些数据。

Selector内部原理实际是在做一个对所注册的channel的轮询访问，不断的轮询(目前就这一个算法)，一旦轮询到一个channel有所注册的事情发生，比如数据来了，他就会站起来报告，交出一把钥匙，让我们通过这把钥匙来读取这个channel的内容。

jdk供的无阻塞I/O（NIO）有效解决了多线程服务器存在的线程开销问题，但在使用上略显得复杂一些。在NIO中使用多线程，主要目的已不是为了应对 每个客户端请求而分配独立的服务线程，而是通过多线程充分使用用多个CPU的处理能力和处理中的等待时间，达到提高服务能力的目的。

这段时间在研究NIO，写篇博客来记住学过的东西。还是从最简单的Hello World开始，client多线程请求server端，server接收client的名字，并返回Hello! ＋名字的字符格式给client。当然实际应用并不这么简单，实际可能是访问文件或者数据库获取信息返回给client。非阻塞的NIO有何神秘之处？

代 码：

1）server端代码

public class HelloWorldServer {

    static int BLOCK = 1024;
    static String name = "";
    protected Selector selector;
    protected ByteBuffer clientBuffer = ByteBuffer.allocate(BLOCK);
    protected CharsetDecoder decoder;
    static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder();

    public HelloWorldServer(int port) throws IOException {
        selector = this.getSelector(port);
        Charset charset = Charset.forName("GB2312");
        decoder = charset.newDecoder();
    }

    // 获取Selector
    protected Selector getSelector(int port) throws IOException {
        ServerSocketChannel server = ServerSocketChannel.open();
        Selector sel = Selector.open();
        server.socket().bind(new InetSocketAddress(port));
        server.configureBlocking(false);
        server.register(sel, SelectionKey.OP_ACCEPT);
        return sel;
    }

    // 监听端口
    public void listen() {
        try {
            for (;;) {
                selector.select();
                Iterator iter = selector.selectedKeys().iterator();
                while (iter.hasNext()) {
                    SelectionKey key = (SelectionKey) iter.next();
                    iter.remove();
                    process(key);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 处理事件
    protected void process(SelectionKey key) throws IOException {
        if (key.isAcceptable()) { // 接收请求
            ServerSocketChannel server = (ServerSocketChannel) key.channel();
            SocketChannel channel = server.accept();
            //设置非阻塞模式
            channel.configureBlocking(false);
            channel.register(selector, SelectionKey.OP_READ);
        } else if (key.isReadable()) { // 读信息
            SocketChannel channel = (SocketChannel) key.channel();
            int count = channel.read(clientBuffer);
            if (count > 0) {
                clientBuffer.flip();
                CharBuffer charBuffer = decoder.decode(clientBuffer);
                name = charBuffer.toString();
                // System.out.println(name);
                SelectionKey sKey = channel.register(selector,
                        SelectionKey.OP_WRITE);
                sKey.attach(name);
            } else {
                channel.close();
            }

            clientBuffer.clear();
        } else if (key.isWritable()) { // 写事件
            SocketChannel channel = (SocketChannel) key.channel();
            String name = (String) key.attachment();

            ByteBuffer block = encoder.encode(CharBuffer
                    .wrap("Hello !" + name));


            channel.write(block);

            //channel.close();

        }
    }

    public static void main(String[] args) {
        int port = 8888;
        try {
            HelloWorldServer server = new HelloWorldServer(port);
            System.out.println("listening on " + port);

            server.listen();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

2）client端代码

public class HelloWorldClient {

    static int SIZE = 10;
    static InetSocketAddress ip = new InetSocketAddress("localhost", 8888);
    static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder();

    static class Message implements Runnable {
        protected String name;
        String msg = "";

        public Message(String index) {
            this.name = index;
        }

        public void run() {
            try {
                long start = System.currentTimeMillis();
                //打开Socket通道
                SocketChannel client = SocketChannel.open();
                //设置为非阻塞模式
                client.configureBlocking(false);
                //打开选择器
                Selector selector = Selector.open();
                //注册连接服务端socket动作
                client.register(selector, SelectionKey.OP_CONNECT);
                //连接
                client.connect(ip);
                //分配内存
                ByteBuffer buffer = ByteBuffer.allocate(8 * 1024);
                int total = 0;

                _FOR: for (;;) {
                    selector.select();
                    Iterator iter = selector.selectedKeys().iterator();

                    while (iter.hasNext()) {
                        SelectionKey key = (SelectionKey) iter.next();
                        iter.remove();
                        if (key.isConnectable()) {
                            SocketChannel channel = (SocketChannel) key
                                    .channel();
                            if (channel.isConnectionPending())
                                channel.finishConnect();
                            channel
                                    .write(encoder
                                            .encode(CharBuffer.wrap(name)));

                            channel.register(selector, SelectionKey.OP_READ);
                        } else if (key.isReadable()) {
                            SocketChannel channel = (SocketChannel) key
                                    .channel();
                            int count = channel.read(buffer);
                            if (count > 0) {
                                total += count;
                                buffer.flip();

                                while (buffer.remaining() > 0) {
                                    byte b = buffer.get();
                                    msg += (char) b;

                                }

                                buffer.clear();
                            } else {
                                client.close();
                                break _FOR;
                            }
                        }
                    }
                }
                double last = (System.currentTimeMillis() - start) * 1.0 / 1000;
                System.out.println(msg + "used time :" + last + "s.");
                msg = "";
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) throws IOException {

        String names[] = new String[SIZE];

        for (int index = 0; index < SIZE; index++) {
            names[index] = "jeff[" + index + "]";
            new Thread(new Message(names[index])).start();
        }

    }
}