- Buffer 
- Channel 
- Selector

- FileChannel （文件io） 
- DatagramChannel （udp數(shù)據(jù)報） 
- SocketChannel （tcp客戶端） 
- ServerSocketChannel （tcp服務(wù)端）

#基本數(shù)據(jù)類型的buffer 
- ByteBuffer 
- CharBuffer 
- DoubleBuffer 
- FloatBuffer 
- IntBuffer 
- LongBuffer 
- ShortBuffer
#文件內(nèi)存映射buffer 
- MappedByteBuffer
#直接內(nèi)存區(qū)buffer 
- DirectBuffer

- SelectionKey.OP_CONNECT 
- SelectionKey.OP_ACCEPT 
- SelectionKey.OP_READ 
- SelectionKey.OP_WRITE

//對selectionKey事件的處理
/**
 * description:
 *
 * @author wkGui
 */
interface ServerHandlerBs {
    void handleAccept(SelectionKey selectionKey) throws IOException;
    String handleRead(SelectionKey selectionKey) throws IOException;
}
/**
 * description:
 *
 * @author wkGui
 */
public class ServerHandlerImpl implements ServerHandlerBs {
    private int bufferSize = 1024;
    private String localCharset = "UTF-8";
    public ServerHandlerImpl() {
    }
    public ServerHandlerImpl(int bufferSize) {
        this(bufferSize, null);
    }
    public ServerHandlerImpl(String localCharset) {
        this(-1, localCharset);
    }
    public ServerHandlerImpl(int bufferSize, String localCharset) {
        this.bufferSize = bufferSize > 0 ? bufferSize : this.bufferSize;
        this.localCharset = localCharset == null ? this.localCharset : localCharset;
    }
    @Override
    public void handleAccept(SelectionKey selectionKey) throws IOException {
        //獲取channel
        SocketChannel socketChannel = ((ServerSocketChannel) selectionKey.channel()).accept();
        //非阻塞
        socketChannel.configureBlocking(false);
        //注冊selector
        socketChannel.register(selectionKey.selector(), SelectionKey.OP_READ, ByteBuffer.allocate(bufferSize));
        System.out.println("建立請求......");
    }
    @Override
    public String handleRead(SelectionKey selectionKey) throws IOException {
        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
        ByteBuffer buffer = (ByteBuffer) selectionKey.attachment();
        String receivedStr = "";
        if (socketChannel.read(buffer) == -1) {
            //沒讀到內(nèi)容關(guān)閉
            socketChannel.shutdownOutput();
            socketChannel.shutdownInput();
            socketChannel.close();
            System.out.println("連接斷開......");
        } else {
            //將channel改為讀取狀態(tài)
            buffer.flip();
            //按照編碼讀取數(shù)據(jù)
            receivedStr = Charset.forName(localCharset).newDecoder().decode(buffer).toString();
            buffer.clear();
            //返回數(shù)據(jù)給客戶端
            buffer = buffer.put(("received string : " + receivedStr).getBytes(localCharset));
            //讀取模式
            buffer.flip();
            socketChannel.write(buffer);
            //注冊selector 繼續(xù)讀取數(shù)據(jù)
            socketChannel.register(selectionKey.selector(), SelectionKey.OP_READ, ByteBuffer.allocate(bufferSize));
        }
        return receivedStr;
    }
}

//服務(wù)端server類
/**
 * description:
 *
 * @author wkGui
 */
public class NioSocketServer {
    private volatile byte flag = 1;
    public void setFlag(byte flag) {
        this.flag = flag;
    }
    public void start() {
        //創(chuàng)建serverSocketChannel，監(jiān)聽8888端口
        try (ServerSocketChannel serverSocketChannel = ServerSocketChannel.open()) {
            serverSocketChannel.socket().bind(new InetSocketAddress(8888));
            //設(shè)置為非阻塞模式
            serverSocketChannel.configureBlocking(false);
            //為serverChannel注冊selector
            Selector selector = Selector.open();
            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
            System.out.println("服務(wù)端開始工作：");
            //創(chuàng)建消息處理器
            ServerHandlerBs handler = new ServerHandlerImpl(1024);
            while (flag == 1) {
                selector.select();
                System.out.println("開始處理請求 ： ");
                //獲取selectionKeys并處理
                Iterator<SelectionKey> keyIterator = selector.selectedKeys().iterator();
                while (keyIterator.hasNext()) {
                    SelectionKey key = keyIterator.next();
                    try {
                        //連接請求
                        if (key.isAcceptable()) {
                            handler.handleAccept(key);
                        }
                        //讀請求
                        if (key.isReadable()) {
                            System.out.println(handler.handleRead(key));
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    //處理完后移除當(dāng)前使用的key
                    keyIterator.remove();
                }
                System.out.println("完成請求處理。");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
//server端啟動類
/**
 * description:
 *
 * @author wkGui
 */
public class ServerMain {
    public static void main(String[] args) {
        NioSocketServer server = new NioSocketServer();
        new Thread(() -> {
            try {
                Thread.sleep(10*60*1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                server.setFlag((byte) 0);
            }
        }).start();
        server.start();
    }
}

//客戶端client類
/**
 * description:
 *
 * @author wkGui
 */
public class NioSocketClient {
    public void start() {
        try (SocketChannel socketChannel = SocketChannel.open()) {
            //連接服務(wù)端socket
            SocketAddress socketAddress = new InetSocketAddress("localhost", 8888);
            socketChannel.connect(socketAddress);
            int sendCount = 0;
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            //這里最好使用selector處理   這里只是為了寫的簡單
            while (sendCount < 10) {
                buffer.clear();
                //向服務(wù)端發(fā)送消息
                buffer.put(("current time : " + System.currentTimeMillis()).getBytes());
                //讀取模式
                buffer.flip();
                socketChannel.write(buffer);
                buffer.clear();
                //從服務(wù)端讀取消息
                int readLenth = socketChannel.read(buffer);
                //讀取模式
                buffer.flip();
                byte[] bytes = new byte[readLenth];
                buffer.get(bytes);
                System.out.println(new String(bytes, "UTF-8"));
                buffer.clear();
                sendCount++;
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
//client啟動類
/**
 * description:
 *
 * @author wkGui
 */
public class ClientMain {
    public static void main(String[] args) {
        new NioSocketClient().start();
    }
}

selector.select(1000);
Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectionKeys.iterator();
while (it.hasNext()) {
    SelectionKey key = it.next();
    it.remove();
    if (key.isAcceptable()) {
        handleAccept(key);
    }
    if (key.isReadable()) {
        handleRead(key);
    }
}

public void handleAccept(SelectionKey key) {
    ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
    SocketChannel sc;
    try {
        sc = ssc.accept();
        sc.configureBlocking(false);
        sc.register(selector, SelectionKey.OP_READ);
        System.out.println(String.format("[server] -- client %s connected.", sc.getRemoteAddress().toString()));
    } catch (IOException e) {
        System.out.println(String.format("[server] -- error occur when accept: %s.", e.getMessage()));
        key.cancel();
    }
}

public void handleRead(SelectionKey key) {
    SocketChannel sc = (SocketChannel) key.channel();
    Client client = (Client) key.attachment();
    ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
    // 如果是第一次連接進(jìn)來，就需要創(chuàng)建一個客戶端對象，存儲起來
    if (client == null) {
        client = new Client(sc);
        clients.add(client);
        key.attach(client);
        byteBuffer.clear();
        // 如果連接還沒有建立，就是要HTTP建立連接
        try {
            sc.read(byteBuffer);
            byteBuffer.flip();
            String response = WebSocketHandler.getResponse(new String(byteBuffer.array()));
            byteBuffer.clear();
            byteBuffer.put(response.getBytes());
            byteBuffer.flip();
            while (byteBuffer.hasRemaining()) {
                sc.write(byteBuffer);
            }
        } catch (IOException e) {
            System.out.println(String.format("[server] -- error occur when read: %s.", e.getMessage()));
        }
        String message = "[系統(tǒng)消息] " + client.toString() + " 加入了群聊";
        broadcast(message.getBytes(), client);
    }
    byteBuffer.clear();
    int read = 0;
    try {
        read = sc.read(byteBuffer);
        if (read > 0) {
            byteBuffer.flip();
            int opcode = byteBuffer.get() & 0x0f;
            // 8表示客戶端關(guān)閉了連接
            if (opcode == 8) {
                System.out.println(String.format("[server] -- client %s connection close.", sc.getRemoteAddress()));
                clients.remove(client);
                String message = "[系統(tǒng)消息] " + client.toString() + " 退出了群聊";
                broadcast(message.getBytes(), client);
                sc.close();
                key.cancel();
                return;
            }
   // 只考慮了最簡單的payload長度情況。
            int len = byteBuffer.get();
            len &= 0x7f;
            byte[] mask = new byte[4];
            byteBuffer.get(mask);
            byte[] payload = new byte[len];
            byteBuffer.get(payload);
            for (int i = 0; i < payload.length; i++) {
                payload[i] ^= mask[i % 4];
            }
            System.out.println(String
                    .format("[server] -- client: [%s], send: [%s].", client.toString(), new String(payload)));
            String message = String.format("[%s]: %s", client.toString(), new String(payload));
            broadcast(message.getBytes(), client);
        } else if (read == -1) {
            System.out.println(String.format("[server] -- client %s connection close.", sc.getRemoteAddress()));
            clients.remove(client);
            String message = "[系統(tǒng)消息] " + client.toString() + " 退出了群聊";
            broadcast(message.getBytes(), client);
            sc.close();
            key.cancel();
        }
    } catch (IOException e) {
        System.out.println(String.format("[server] -- error occur when read: %s.", e.getMessage()));
    }
}

public class WebSocketHandler {
    private static String APPEND_STRING = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
    static class Header {
        private Map<String, String> properties = new HashMap<>();
        public String get(String key) {
            return properties.get(key);
        }
    }
    private WebSocketHandler() {}
    private static Header phrase(String request) {
        Header header = new Header();
        String[] pros = request.split("\r\n");
        for (String pro : pros) {
            if (pro.contains(":")) {
                int index = pro.indexOf(":");
                String key = pro.substring(0, index).trim();
                String value = pro.substring(index + 1).trim();
                header.properties.put(key, value);
            }
        }
        return header;
    }
    public static String getResponse(String request) {
        Header header = phrase(request);
        String acceptKey = header.get("Sec-WebSocket-Key") + APPEND_STRING;
        MessageDigest sha1;
        try {
            sha1 = MessageDigest.getInstance("sha1");
            sha1.update(acceptKey.getBytes());
            acceptKey = new String(Base64.getEncoder().encode(sha1.digest()));
        } catch (NoSuchAlgorithmException e) {
            System.out.println("fail to encode " + e.getMessage());
            return null;
        }
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("HTTP/1.1 101 Switching Protocols\r\n").append("Upgrade: websocket\r\n")
                     .append("Connection: Upgrade\r\n").append("Sec-WebSocket-Accept: " + acceptKey + "\r\n")
                     .append("\r\n");
        return stringBuilder.toString();
    }
}

/**
 * @author XinHui Chen
 * @date 2020/2/8 19:20
 */
public class Client {
    private SocketChannel socketChannel = null;
    private String id = null;
    public SocketChannel getSocketChannel() {
        return socketChannel;
    }
    public String getId() {
        return id;
    }
    Client(SocketChannel socketChannel) {
        this.socketChannel = socketChannel;
        this.id = UUID.randomUUID().toString();
    }
    @Override
    public String toString() {
        try {
            return id + " " + socketChannel.getRemoteAddress().toString();
        } catch (IOException e) {
            System.out.println(e.getMessage());
            return null;
        }
    }
}