常见IO模型（BIO、NIO、AIO）

1.网络模型

a.编程模型 TCP UDP
- TCP->可靠连接、使命必达、速度慢
- UDP->不可靠、速度快

1.常见的IO模型

blocking IO == Old IO（BIO）

案例：如果不开线程，那么就会阻塞。

public class Server {
    public static void main(String[] args) throws Exception {
        ServerSocket ss = new ServerSocket();
        ss.bind(new InetSocketAddress("localhost", 8888));
        new Thread(()->{
            try {
                Socket s = ss.accept();
                BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
                System.out.println(br.readLine());
                br.close();
                s.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
        ss.close();
    }
}

Non-Blocking IO（NIO）->Java的API还不如C

调用Linux底层的epoll()，使用一个Channel，用Selector进行接受

ServerSocket是阻塞式的、Channel是双向的。

模型1

public class Server {
    public static void main(String[] args) throws Exception {
        ServerSocketChannel ssc = ServerSocketChannel.open();
        ssc.socket().bind(new InetSocketAddress("localhost", 8888));
        ssc.configureBlocking(false);

        System.out.println("server started, listening on: " + ssc.getLocalAddress());
        Selector selector = Selector.open();// selector是个大管家，进行调用epoll
        ssc.register(selector, SelectionKey.OP_ACCEPT);// 监听在OP_ACCEPT（连接操作）操作下进行处理

        while (true) {
            selector.select();// 轮训，无事件发生就进行等待
            Set<SelectionKey> keys = selector.selectedKeys();
            Iterator<SelectionKey> it = keys.iterator();
            while (it.hasNext()) {
                SelectionKey key = it.next();
                it.remove();
                handle(key);
            }
        }
    }

    private static void handle(SelectionKey key) {
        if(key.isAcceptable()) {// 写
            try {
                ServerSocketChannel ssc = (ServerSocketChannel) key.channel();// 新的通道
                SocketChannel sc = ssc.accept();
                sc.configureBlocking(false);
                sc.register(key.selector(), SelectionKey.OP_READ);// 设置为读
            } catch (IOException e) {
                e.printStackTrace();
            }
        }else if (key.isReadable()) {// 读
            SocketChannel sc = null;
            try{
                sc = (SocketChannel) key.channel();
                ByteBuffer buffer = ByteBuffer.allocate(512);
                buffer.clear();
                int len = sc.read(buffer);
                if(len != -1) {
                    System.out.println(new String(buffer.array(), 0, len));
                }
                ByteBuffer bufferToWrite = ByteBuffer.wrap("HelloClient".getBytes());
                sc.write(bufferToWrite);
            }catch (IOException e) {
                e.printStackTrace();
            }finally {
                if(sc != null) {
                    try {
                        sc.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

模型2