分布式开发

概念

网络编程知识

1. DNS域名系统(属于应用层)：用于将域名解析成IP(单域名解析多IP可实现负载均衡)
2. IP网际互连协议：用于实现广域网中的数据传输(ip是根据网络拓扑分配的，解决我在哪的问题)
3. MAC：用于实现局域网中的数据传输(mac是由网卡制造商分配的，解决我是谁的问题)
4. ARP地址解析协议：映射Mac地址与IP地址的协议 - 核心①映射缓存 ②ARP请求广播(用于构建映射缓存)
5. TCP协议：三次握手和四次挥手
6. SSL安全套接字协议：加密 ①客户端hello ②服务端hello+证书+验证性加密数据 ③客户端验证 + 密钥交换 + 验证性加密数据 ④服务端验证
7. HTTP协议(应用层协议)：

Socket 和 IO多路复用

Socket编程 - BIO(同步阻塞IO)：每一个连接对应一个线程，执行Socket的读写操作均会阻塞线程
SocketChannel编程 - NIO(同步非阻塞IO)：轮询 - 每一个请求对应一个线程，线程会阻塞在selector.select()，当出现活跃请求时，需轮询查找活跃请求并处理,O(n) 同步IO(需等待IO完成)
AsynchronousSocketChannel编程 - AIO(异步非阻塞IO)：回调 - 每一个有效请求对应一个线程，当出现活跃请求时，直接调用请求对应的回调方法实现处理,O(1) 异步IO(Future实现)

select: 当事件发生，但不知道具体是哪个流，通过轮询查找，时间复杂度O(N)
poll: 作用等同于select，链表结构存储(无限大)，通过轮询查找, 时间复杂度O(N)
epoll: 事件驱动，callback方式，时间复杂度O(1) – 采用mmap共享内存实现内核-用户空间的数据传递

demo

BIO

核心组件：①ServerSocket建立服务器监听，②Socket代表一个连接
阻塞IO，socket调用读写方法时，会进入阻塞，直到数据到达

public class ServerSocketDemo {
    private static ExecutorService executors = Executors.newFixedThreadPool(4);

    public static void main(String[] args) {
        // 服务端开启Socket监听
        try (ServerSocket serverSocket = new ServerSocket(8080);){
            while(true){
                // 当请求到达时，新建线程处理对应socket
                Socket socket = serverSocket.accept();
                executors.execute(()->ServerSocketHandler.handler(socket));
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

public class ServerSocketHandler {
    public static void handler(Socket socket){
        // server中socket流的获取与client中流的获取顺序需相反(否则可能资源死等)
        try (InputStream is = socket.getInputStream();
             ObjectInputStream ois = new ObjectInputStream(is);

             OutputStream os = socket.getOutputStream();
             ObjectOutputStream oos = new ObjectOutputStream(os);)
        {
            // 读操作(在数据未到达之前将阻塞)
            User msg = (User) ois.readObject();
            System.out.println(Thread.currentThread().getName() + " - 读入：" + msg);

            // 写操作
            oos.writeObject(msg);
            oos.flush();
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

public class ClientSocketDemo {
    public static void main(String[] args) {
        // 客户端直接采用Socket建立连接
        try(Socket socket = new Socket("localhost",8080);){
            ClientSocketHandler.handler(socket);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

public class ClientSocketHandler {
    public static void handler(Socket socket){
        // server中socket流的获取与client中流的获取顺序需相反(否则可能资源死等)
        try (OutputStream os = socket.getOutputStream();
             ObjectOutputStream oos = new ObjectOutputStream(os);

             InputStream is = socket.getInputStream();
             ObjectInputStream ois = new ObjectInputStream(is);
        ){
            // 写操作 - 执行操作也需相反。。。
            oos.writeObject(new User("kiqi",18));
            oos.flush();

            // 读操作
            User msg = (User) ois.readObject();
            System.out.println("客户端 - 读入：" + msg);

            Thread.sleep(1000);
        } catch (IOException | ClassNotFoundException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

NIO

核心组件：①selector，用于判断是否存在活跃事件 ②ServerSocketChannel，用于连接事件通道 ③SocketChannel，用于读写事件通道 ④register(selector, SelectionKey.OP_ACCEPT);
非阻塞IO，将socketChannel与相应事件注册到selector，当出现活跃事件时，selector.select()将解除阻塞，通过轮询获取并处理已经到达的事件(只能做到存在活跃事件，不知道具体是哪一个)

public class ServerSocketChannelDemo {
    private static Selector selector;

    public static void main(String[] args) {
        try {
            // 开启selector功能(底层由操作系统提供支持 select,poll或epoll)
            selector = Selector.open();
            
            // ServerSocketChannel,开启服务端口监听
            ServerSocketChannel channel = ServerSocketChannel.open();
            channel.configureBlocking(false);
            channel.socket().bind(new InetSocketAddress(8080));

            // 将ServerSocketChannel与对应事件绑定到selector，当事件发生时，selector.select()将接触阻塞
            channel.register(selector, SelectionKey.OP_ACCEPT);
            while (true){
                // 阻塞，直到出现活跃事件
                selector.select();
                
                // 无法获知具体事件，需轮询判断
                Set<SelectionKey> selectionKeySet = selector.selectedKeys();
                Iterator<SelectionKey> iterator = selectionKeySet.iterator();
                while (iterator.hasNext()){
                    SelectionKey selectionKey = iterator.next();
                    iterator.remove();
                    // 链接事件
                    if(selectionKey.isAcceptable()){
                        handleAccept(selectionKey);
                    // 读事件
                    }else if(selectionKey.isReadable()){
                        handleRead(selectionKey);
                        ((SocketChannel)selectionKey.channel()).write(ByteBuffer.wrap("server_msg - 啥玩意啊，这么难用".getBytes()));
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void handleAccept(SelectionKey selectionKey) {
        // 处理连接事件，并将该连接通道的读事件注册到Selector
        ServerSocketChannel serverSocketChannel = (ServerSocketChannel) selectionKey.channel();
        try {
            SocketChannel channel = serverSocketChannel.accept();
            channel.configureBlocking(false);
            channel.register(selector,SelectionKey.OP_READ);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void handleRead(SelectionKey selectionKey) {
        // 处理读事件
        SocketChannel channel = (SocketChannel) selectionKey.channel();
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        try {
            channel.read(byteBuffer);
            System.out.println("Server - 嘛玩意啊，超级难用 - " + new String(byteBuffer.array()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

public class ClientSocketChannelDemo {
    private static Selector selector;

    public static void main(String[] args) {
        try {
            // 开启selector功能(底层由操作系统提供支持 select,poll或epoll)
            selector = Selector.open();

            // SocketChannel,建立连接通道
            SocketChannel channel = SocketChannel.open();
            channel.configureBlocking(false);
            channel.connect(new InetSocketAddress("localhost",8080));

            // 将连接事件注册到selector
            channel.register(selector, SelectionKey.OP_CONNECT);
            while (true) {
                // 阻塞，直到连接事件成功
                selector.select();
                Set<SelectionKey> selectionKeySet = selector.selectedKeys();
                Iterator<SelectionKey> iterator = selectionKeySet.iterator();
                while (iterator.hasNext()) {
                    SelectionKey selectionKey = iterator.next();
                    iterator.remove();
                    // 连接就绪，处理连接事件
                    if (selectionKey.isConnectable()) {
                        handleConnect(selectionKey);
                        ((SocketChannel)selectionKey.channel()).write(ByteBuffer.wrap("server_msg - 啥玩意啊，这么难用".getBytes()));
                    // 处理读事件
                    } else if (selectionKey.isReadable()) {
                        handleRead(selectionKey);
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void handleConnect(SelectionKey selectionKey) {
        SocketChannel channel = (SocketChannel) selectionKey.channel();
        try {
            // 未调用channel.finishConnect()的连接，处于连接中，还无法进行读写
            if(channel.isConnectionPending()){
                channel.finishConnect();
            }
            channel.configureBlocking(false);
            // 注册读事件
            channel.register(selector,SelectionKey.OP_READ);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void handleRead(SelectionKey selectionKey) {
        // 处理读事件
        SocketChannel channel = (SocketChannel) selectionKey.channel();
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        try {
            channel.read(byteBuffer);
            System.out.println("Client - 嘛玩意啊，超级难用 - " + new String(byteBuffer.array()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

AIO

核心组件：①AsynchronousServerSocketChannel，用于建立服务器监听。 ②channel.accept()，接受连接， ③AsynchronousSocketChannel，用于处理连接的读写事件
④Future，用于异步等待IO完成 ⑤CompletionHandler接口，当IO完成后，执行的回调接口方法
异步非阻塞式IO，①提供了回调式处理，当活跃事件发生时，直接回调接口方法O(1) ②Future<?>异步IO(内部建立了内核空间与用户空间的内存)。

// AsynchronousSocketChannel代表一个连接，通过连接完成读写事件处理
// 方式一：CompletionHandler接口回调
public class AysnServerSocketChannelDemo {
    public static void main(String[] args) throws InterruptedException {
        try {
            // 服务端建立端口监听
            AsynchronousServerSocketChannel channel = AsynchronousServerSocketChannel.open();
            channel.bind(new InetSocketAddress(8080));

            // 接受连接事件，当事件发生并且执行完IO后，会回调CompletionHandler接口
            channel.accept(null, new CompletionHandler<AsynchronousSocketChannel, Object>() {
                @Override
                public void completed(AsynchronousSocketChannel result, Object attachment) {
                    // 需再次开启接受连接事件
                    channel.accept(null, this);

                    // 处理已连接通道
                    handle(result);
                }

                // 失败时执行逻辑
                @Override
                public void failed(Throwable exc, Object attachment) {
                    exc.printStackTrace();
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
        Thread.sleep(100000);
    }
    
    public static void handle(AsynchronousSocketChannel channel) {
        try {
            final ByteBuffer buffer = ByteBuffer.allocate(1024);
            final long timeout = 10L;
            // 读事件，完成IO后回调CompletionHandler接口方法
            channel.read(buffer, timeout, TimeUnit.SECONDS, null, new CompletionHandler<Integer, Object>() {
                @Override
                public void completed(Integer result, Object attachment) {
                    System.out.println("read:" + result);
                    if (result == -1) {
                        try {
                            channel.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                        return;
                    }
                    buffer.flip();
                    System.out.println("received message:" + Charset.forName("UTF-8").decode(buffer));
                    buffer.clear();
                    channel.read(buffer, timeout, TimeUnit.SECONDS, null, this);
                }
                @Override
                public void failed(Throwable exc, Object attachment) {
                    exc.printStackTrace();
                }
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

// 方式二：Future<?>.get()异步方法等待结果
public class AsynClientSocketChannelDemo {

    private static AsynchronousSocketChannel client;

    public static void main(String[] args) throws InterruptedException {
        try {
            // 创建连接通道并建立连接
            client = AsynchronousSocketChannel.open();
            Future<?> future = client.connect(new InetSocketAddress("localhost",8080));
            // get()方法，等待连接完成
            future.get();
            
            // 执行读写时间
            client.write(ByteBuffer.wrap("？？？".getBytes()));
        } catch (IOException | InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        Thread.sleep(100000);
    }
}