IO模型

IO模型

IO模型就是说用什么样的通道进行数据的发送和接收,Java共支持3种网络编程IO模式:BIO,NIO,AIO

BIO (Blocking IO)

同步阻塞IO模型,一个客户端对应一个服务端

bio.png

服务端:

@Slf4j
public class BIOServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        while (true) {
            log.info("服务端已启动,等待连接");
            // 阻塞
            Socket socket = serverSocket.accept();
            log.info("客户端已连接");

            // 单线程处理链接
            // handler(socket);

            // 多线程处理链接
            new Thread(new Runnable() {
                @SneakyThrows
                @Override
                public void run() {
                    log.info("local-thread-{}", Thread.currentThread().getName());
                    handler(socket);
                }
            }).start();
        }
    }

    private static void handler(Socket socket) throws IOException {
        byte[] bytes = new byte[1024];
        log.info("获取客户端发送数据");
        // 接收数据,阻塞方法,没有数据可读时就阻塞
        int read = socket.getInputStream().read(bytes);
        if (read != -1) {
            log.info("接收客户数据: {}", new String(bytes, 0, read));
        }

        // 响应客户端
        OutputStream outputStream = socket.getOutputStream();
        outputStream.write("server is connecting".getBytes());
        outputStream.flush();
    }
}

客户端:

@Slf4j
public class BIOClient {
    private static final String HOST = "localhost";
    private static final int PORT = 8080;

    public static void main(String[] args) throws IOException {
        Socket socket = new Socket(HOST, PORT);
        // 发送数据
        OutputStream os = socket.getOutputStream();
        os.write("request server connect".getBytes());
        os.flush();

        // 接收数据
        byte[] bytes = new byte[1024];
        InputStream is = socket.getInputStream();
        int read = is.read(bytes);
        if (read != -1) {
            log.info("接收到来自服务端的数据: {}", new String(bytes, 0, read));
        }

        socket.close();
    }
}

缺点

  • 1、IO代码里read操作是阻塞操作,如果连接不做数据读写操作会导致线程阻塞,浪费资源
  • 2、如果线程很多,会导致服务器线程太多,压力太大,比如C10K问题

应用场景

BIO 方式适用于连接数目比较小且固定的架构,这种方式对服务器资源要求比较高,但程序简单易理解。

NIO (NON Blocking IO)

同步非阻塞IO模型,服务器实现模式为一个线程可以处理多个请求(连接),客户端发送的连接请求都会注册到多路复用器selector上,
多路复用器轮询到连接有IO请求就进行处理,JDK1.4开始引入。

NIO.png

普通模型:

@Slf4j
public class NIOServer {
    static List<SocketChannel> channelList = Lists.newArrayList();

    public static void main(String[] args) throws IOException {
        // 创建 NIO 通道
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        // 绑定服务端口地址
        serverSocketChannel.socket().bind(new InetSocketAddress(8080));
        // 设置通道为非阻塞模式
        serverSocketChannel.configureBlocking(false);
        log.info("服务端已启动,等待连接");

        while (true) {
            // 非阻塞模式 accept() 方法不会阻塞。阻塞模式则会阻塞,即 socketChannel.configureBlocking(ture)
            // NIO的非阻塞是由操作系统内部实现的,底层调用了linux内核的accept函数
            SocketChannel socketChannel = serverSocketChannel.accept();
            if (!ObjectUtils.isEmpty(socketChannel)) {
                log.info("客户端已连接: {}", socketChannel.getRemoteAddress());
                socketChannel.configureBlocking(false);
                // 连接成功放到 channelList 中
                channelList.add(socketChannel);
            }

            // 读取 channel
            Iterator<SocketChannel> iterator = channelList.iterator();
            while (iterator.hasNext()) {
                SocketChannel channel = iterator.next();
                ByteBuffer byteBuffer = ByteBuffer.allocate(128);

                // 非阻塞模式 read() 方法不会阻塞。阻塞模式则会阻塞
                int read = channel.read(byteBuffer);
                if (read > 0) {
                    log.info("接收客户 {}, 数据: {}", channel.getRemoteAddress(), new String(byteBuffer.array()));
                } else if (read < 0) {
                    //
                    iterator.remove();
                    log.info("客户端已断开连接");
                }
            }
        }
    }
}

如上,如果有很多连接,每一个连接都需要通过iterator遍历获取数据,如果该连接无数据发送,则会产生很多无用的遍历。

多路复用器模型:

@Slf4j
public class NIOSelectorServer {

    public static void main(String[] args) throws IOException {
        // 创建 NIO 通道
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        // 绑定服务端口地址
        serverSocketChannel.socket().bind(new InetSocketAddress(8080));
        // 设置通道为非阻塞模式
        serverSocketChannel.configureBlocking(false);
        // 打开 Selector 处理 Channel,即创建 epoll
        Selector selector = Selector.open();
        // Channel 注册到 selector 上,并 selector 对客户端 accept 操作监听
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        log.info("服务端已启动,等待连接");

        while (true) {
            // 阻塞等待需要处理的事件发生
            selector.select();
            // 获取 selector 中注册的全部事件中的 selectedKeys 实例
            Set<SelectionKey> selectionKeys = selector.selectedKeys();

            Iterator<SelectionKey> keyIterator = selectionKeys.iterator();
            // 遍历对 selectionKeys 事件进行处理
            while (keyIterator.hasNext()) {
                SelectionKey selectionKey = keyIterator.next();
                // 是 OP_ACCEPT 事件,则进行后续的获取数据和事件注册
                if (selectionKey.isAcceptable()) {
                    ServerSocketChannel serverSocket = (ServerSocketChannel) selectionKey.channel();
                    SocketChannel socketChannel = serverSocket.accept();
                    socketChannel.configureBlocking(false);
                    // 注册 OP_READ 事件,需要给客户端发送数据,则注册 OP_WRITE 即可
                    socketChannel.register(selector, SelectionKey.OP_READ);
                    log.info("客户端已连接: {}", socketChannel.getRemoteAddress());

                    // 是 OP_READ 事件,则获取客户端发送的数据
                } else if (selectionKey.isReadable()) {
                    SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
                    ByteBuffer byteBuffer = ByteBuffer.allocate(128);
                    int read = socketChannel.read(byteBuffer);
                    if (read > 0) {
                        log.info("接收客户 {}, 数据: {}", socketChannel.getRemoteAddress(), new String(byteBuffer.array()));
                    } else if (read < 0) {
                        socketChannel.close();
                        log.info("客户端已断开连接");
                    }
                }
                // selectionKeys 没有对应事件即移除,防止下次 seletor 重复处理
                keyIterator.remove();
            }
        }
    }
}

NIO 有三大核心组件: Channel(通道), Buffer(缓冲区),Selector(多路复用器)

1、channel 类似于流,每个 channel 对应一个 buffer 缓冲区,buffer 底层就是个数组

2、channel 会注册到 selector 上,由 selector 根据 channel 读写事件的发生将其交由某个空闲的线程处理

3、NIO 的 Bufferchannel 都是既可以读也可以写

应用场景

NIO方式适用于连接数目多且连接比较短(轻操作) 的架构, 比如聊天服务器, 弹幕系统, 服务器间通讯,编程比较复杂

AIO (NIO 2.0)

异步非阻塞, 由操作系统完成后回调通知服务端程序启动线程去处理, 一般适用于连接数较多且连接时间较长的应用

异步模型:

@Slf4j
public class AIOServer {
    public static void main(String[] args) throws IOException, InterruptedException {
        AsynchronousServerSocketChannel assc = AsynchronousServerSocketChannel.open().bind(new InetSocketAddress(8080));
        assc.accept(null, new CompletionHandler<AsynchronousSocketChannel, Object>() {
            @SneakyThrows
            @Override
            public void completed(AsynchronousSocketChannel socketChannel, Object attachment) {
                log.info("connet -- {}", Thread.currentThread().getName());
                // 在此接收客户端连接,否则后面的客户端连接不上服务端
                assc.accept(attachment, this);
                log.info("客户端:{}", socketChannel.getRemoteAddress());
                ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
                socketChannel.read(byteBuffer, byteBuffer, new CompletionHandler<Integer, ByteBuffer>() {
                    @Override
                    public void completed(Integer result, ByteBuffer attachment) {
                        log.info("read -- {}", Thread.currentThread().getName());
                        byteBuffer.flip();
                        log.info("客户端请求数据:{}", new String(byteBuffer.array(), 0, result));
                        socketChannel.write(ByteBuffer.wrap("This is response data".getBytes()));
                    }

                    @Override
                    public void failed(Throwable exc, ByteBuffer attachment) {
                        log.error("read error: {}", exc.getMessage());
                        exc.printStackTrace();
                    }
                });
            }

            @Override
            public void failed(Throwable exc, Object attachment) {
                log.error("connect error: {}", exc.getMessage());
                exc.printStackTrace();
            }
        });

        log.info("main -- {}", Thread.currentThread().getName());
        Thread.sleep(Integer.MAX_VALUE);
    }
}

应用场景

AIO方式适用于连接数目多且连接比较长(重操作)的架构,JDK7 开始支持

对比

1614160645531.jpg

资料

【公众号】网络 IO 演变发展过程和模型介绍

【B站视频】IO多路复用底层原理全解


收录时间: 2021/02/24

推荐阅读更多精彩内容