第一章 java nio三大组件与使用姿势

本案例来源于《netty权威指南》

一、三大组件

• Selector：多路复用器。轮询注册在其上的Channel，当发现某个或者多个Channel处于“就绪状态”后（accept接收连接事件、connect连接完成事件、read读事件、write写事件），从阻塞状态返回就绪的Channel的SelectionKey集合，之后进行IO操作。
• Channel：封装了socket。
  • ServerSocketChannel：封装了ServerSocket，用于accept客户端连接请求；
  • SocketChannel：一对SocketChannel组成一条虚电路，进行读写通信
• Buffer：用于存取数据，最主要的是ByteBuffer
  • position：下一个将被操作的字节位置
  • limit：在写模式下表示可以进行写的字节数，在读模式下表示可以进行读的字节数
  • capacity：Buffer的大小

二、服务端代码

1、服务端启动类

public class Server {
    public static void main(String[] args) throws IOException {
        new Thread(new ServerHandler(8080), "server-1").start();
    }
}

创建一个任务ServerHandler，然后创建一条线程，启动执行该任务。

2、逻辑处理类

public class ServerHandler implements Runnable {
    private Selector selector;
    private ServerSocketChannel ssChannel;

    public ServerHandler(int port) {
        try {
            //等价于 Selector selector = SelectorProvider.provider().openSelector();
            selector = Selector.open();
            //等价于 SelectorProvider.provider().openServerSocketChannel()
            ssChannel = ServerSocketChannel.open();
            ssChannel.configureBlocking(false);
            ssChannel.bind(new InetSocketAddress(port), 1024);
            ssChannel.register(selector, SelectionKey.OP_ACCEPT);
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    public void run() {
        for (; ; ) {
            try {
                selector.select();
                Iterator<SelectionKey> it = selector.selectedKeys().iterator();
                while (it.hasNext()) {
                    SelectionKey key = it.next();
                    it.remove();
                    handleInput(key);
                }
            } catch (Throwable t) {
                t.printStackTrace();
            }
        }

    }

    private void handleInput(SelectionKey key) throws IOException {
        if (key.isValid()) {
            // 处理新接入的请求消息
            if (key.isAcceptable()) {
                // Accept the new connection
                ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                SocketChannel sc = ssc.accept();
                sc.configureBlocking(false);
                // Add the new connection to the selector
                sc.register(selector, SelectionKey.OP_READ);
            }
            if (key.isReadable()) {
                // Read the data
                SocketChannel sc = (SocketChannel) key.channel();
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                int readBytes = sc.read(readBuffer);
                if (readBytes > 0) {
                    readBuffer.flip();
                    byte[] bytes = new byte[readBuffer.remaining()];
                    readBuffer.get(bytes);
                    String body = new String(bytes, "UTF-8");
                    System.out.println("The time server receive order : "
                            + body);
                    String currentTime = "QUERY TIME ORDER"
                            .equalsIgnoreCase(body) ? new java.util.Date(
                            System.currentTimeMillis()).toString()
                            : "BAD ORDER";
                    doWrite(sc, currentTime);
                } else if (readBytes < 0) {
                    // 对端链路关闭
                    key.cancel();
                    sc.close();
                } else
                    ; // 读到0字节，忽略
            }
        }
    }

    private void doWrite(SocketChannel channel, String response)
            throws IOException {
        if (response != null && response.trim().length() > 0) {
            byte[] bytes = response.getBytes();
            ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
            writeBuffer.put(bytes);
            writeBuffer.flip();
            channel.write(writeBuffer);
        }
    }
}

步骤：

1、创建一个Selector和ServerSocketChannel实例

2、配置ServerSocketChannel实例为非阻塞

3、ServerSocketChannel实例bind端口

4、将ServerSocketChannel实例注册到selector上，监听OP_ACCEPT事件

下面的任务在Server创建的新的线程中执行，不影响主线程执行其他逻辑

5、之后进入死循环

5.1、使用select.select()阻塞等待就绪事件（这里是等待OP_ACCEPT事件），一旦有有就绪事件到达，立即向下执行

5.2、使用selector.selectedKeys()获取已经就绪的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之后循环遍历

5.3、从迭代器删除该SelectionKey，防止下一次再被遍历到

5.4、如果SelectionKey==OP_ACCEPT，则通过ServerSocketChannel.accept()创建SocketChannel，该SocketChannel是后续真正的与客户端的SocketChannel进行通信的实体

5.5、配置新创建的SocketChannel实例为非阻塞，然后将该SocketChannel实例注册到selector实例上，监听OP_READ事件

5.6、等客户端发出请求数据时，此处监听到SelectionKey==OP_READ，则创建ByteBuffer实例，将SocketChannel中的数据读取到ByteBuffer中，然后再创建ByteBuffer将信息写回到SocketChannel（也就是说数据的读写一定要通过Buffer）

三、客户端代码

1、客户端启动类

public class Client {
    public static void main(String[] args) {
        new Thread(new ClientHandler("127.0.0.1", 8080), "client-1").start();
    }
}

创建一个任务ClientHandler，然后创建一条线程，启动执行该任务。

2、逻辑处理类

public class ClientHandler implements Runnable {
    private String host;
    private int port;

    private Selector selector;
    private SocketChannel socketChannel;

    public ClientHandler(String host, int port) {
        this.host = host;
        this.port = port;
        try {
            selector = Selector.open();
            socketChannel = SocketChannel.open();
            socketChannel.configureBlocking(false);
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    public void run() {
        try {
            doConnect();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
        while (true) {
            try {
                selector.select();
                Iterator<SelectionKey> it = selector.selectedKeys().iterator();
                while (it.hasNext()) {
                    SelectionKey key = it.next();
                    it.remove();
                    handleInput(key);
                }
            } catch (Exception e) {
                e.printStackTrace();
                System.exit(1);
            }
        }
    }

    private void handleInput(SelectionKey key) throws IOException {
        if (key.isValid()) {
            // 判断是否连接成功
            SocketChannel sc = (SocketChannel) key.channel();
            if (key.isConnectable()) {
                if (sc.finishConnect()) {
                    sc.register(selector, SelectionKey.OP_READ);
                    doWrite(sc);
                } else
                    System.exit(1);// 连接失败，进程退出
            } else if (key.isReadable()) {
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                int readBytes = sc.read(readBuffer);
                if (readBytes > 0) {
                    readBuffer.flip();
                    byte[] bytes = new byte[readBuffer.remaining()];
                    readBuffer.get(bytes);
                    String body = new String(bytes, "UTF-8");
                    System.out.println("Now is : " + body);
                } else if (readBytes < 0) {
                    // 对端链路关闭
                    key.cancel();
                    sc.close();
                } else
                    ; // 读到0字节，忽略
            }
        }

    }

    private void doConnect() throws IOException {
        // 如果直接连接成功，则注册到多路复用器上，发送请求消息，读应答
        if (socketChannel.connect(new InetSocketAddress(host, port))) {
            socketChannel.register(selector, SelectionKey.OP_READ);
            doWrite(socketChannel);
        } else
            socketChannel.register(selector, SelectionKey.OP_CONNECT);
    }

    private void doWrite(SocketChannel sc) throws IOException {
        byte[] req = "QUERY TIME ORDER".getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
        writeBuffer.put(req);
        writeBuffer.flip();
        sc.write(writeBuffer);
        if (!writeBuffer.hasRemaining())
            System.out.println("Send order 2 server succeed.");
    }
}

步骤：

1、创建一个Selector和SocketChannel实例

2、配置SocketChannel实例为非阻塞

下面的任务在Cilent创建的新的线程中执行，不影响主线程执行其他逻辑

3、SocketChannel.connect连接到server端，如果连接没有马上成功，将该SocketChannel实例注册到selector上，监听OP_CONNECT事件；如果连接成功，将该SocketChannel实例注册到selector上，监听OP_READ事件，之后写数据给server端

4、之后进入死循环

4.1、使用select.select()阻塞等待就绪事件，一旦有有就绪事件到达，立即向下执行

4.2、使用selector.selectedKeys()获取已经就绪的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之后循环遍历

4.3、从迭代器删除该SelectionKey，防止下一次再被遍历到

4.4、如果SelectionKey==OP_CONNECT，将该SocketChannel实例注册到selector上，监听OP_READ事件，之后写数据给server端；如果监听到SelectionKey==OP_READ，则创建ByteBuffer实例，将SocketChannel中的数据读取到ByteBuffer中