一、案例要求

例項要求:

1. 編寫一個 NIO 群聊系統， 實現伺服器端和客戶端之間的資料簡單通訊（非 阻塞）
2. 實現多人群聊
3. 伺服器端： 可以監測使用者上線， 離線，並實現訊息轉發功能
4. 客戶端： 通過channel 可以無阻塞傳送訊息給其它所有使用者，同時可以接受 其它使用者傳送的訊息(有伺服器轉發得到)
5. 目的： 進一步理解NIO非阻塞網路程式設計機制

實現效果：

思路步驟：

1. 先編寫伺服器端
   • 伺服器啟動並監聽 6667
   • 伺服器接收客戶端資訊，並實現轉發 [處理上線和離線]
2. 編寫客戶端
   • 連線伺服器
   • 傳送訊息
   • 接收伺服器訊息

二、伺服器端

public class GroupChatServer
 
 {

    //定義屬性
    private Selector selector;
    private ServerSocketChannel listenChannel;
    private static final int PORT = 6667;

    //構造器
    //初始化工作
    public GroupChatServer() {

        try {

            //得到選擇器
            selector = Selector.open();
            System.out.println("selector = " + selector);

            //獲取 ServerSocketChannel
 

            listenChannel = ServerSocketChannel.open();
            //繫結埠
            listenChannel.socket().bind(new InetSocketAddress(PORT));
            //設定非阻塞模式
            listenChannel.configureBlocking(false);
            //將該 listenChannel 註冊到selector
            listenChannel.register(selector, SelectionKey.OP_ACCEPT);

        } catch
 
 (IOException e) {
            e.printStackTrace();
        }
    }

    //伺服器監聽
    public void listen() {
        System.out.println("監聽執行緒: " + Thread.currentThread().getName());

        try {

            //迴圈處理
            while (true) {
                int count = selector.select();
                //有事件需要處理
                if (count > 0) {

                    //遍歷得到的 selectionKey 集合
                    Iterator<SelectionKey> keyIterator = selector.selectedKeys().iterator();
                    while (keyIterator.hasNext()) {

                        //取出 SelectionKey
                        SelectionKey key = keyIterator.next();

                        //監聽到accept
                        if (key.isAcceptable()) {
                            //建立一個SocketChannel
                            SocketChannel socketChannel = listenChannel.accept();
                            //設定非阻塞模式
                            socketChannel.configureBlocking(false);
                            //註冊到選擇器
                            socketChannel.register(selector, SelectionKey.OP_READ);

                            //提示
                            System.out.println(socketChannel.getRemoteAddress() + " 上線");

                        }

                        //通道傳送read事件，即通道是可讀的狀態
                        if (key.isReadable()) {
                            //處理讀（專門寫方法...）
                            read(key);
                        }

                        //當前的key 刪除，防止重複處理
                        keyIterator.remove();
                    }

                } else {
                    System.out.println("等待...");
                }
            }


        }catch (IOException e) {
            e.printStackTrace();
        }
    }

    //讀取客戶端資訊
    private void read(SelectionKey key) {
        //得到關聯的 Channel
        SocketChannel socketChannel = null;

        try {
            //得到 channel
            socketChannel = (SocketChannel) key.channel();
            //建立 buffer
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            //讀取資料
            int count = socketChannel.read(buffer);
            //根據 count 的值去做處理
            if (count > 0) {
                //把快取區的資料轉成字串
                String msg = new String(buffer.array());
                //輸出該訊息
                System.out.println("form 客戶端：" + msg);

                //轉發訊息：向其它的客戶端轉發訊息(去掉自己), 專門寫一個方法來處理
                sentInfoToOtherClients(msg, socketChannel);
            }
        }catch (IOException e) {
            try {
                System.out.println(socketChannel.getRemoteAddress() + " 離線了..");
                //取消註冊
                key.cancel();
                //關閉通道
                socketChannel.close();
            } catch (IOException e2) {
                e2.printStackTrace();
            }
        }
    }

    //轉發訊息給其它客戶(通道)
    private void sentInfoToOtherClients(String msg, SocketChannel self) throws IOException{
        System.out.println("伺服器轉發訊息中...");
        System.out.println("伺服器轉發資料給客戶端執行緒: " + Thread.currentThread().getName());

        //遍歷 所有註冊到selector 上的 SocketChannel,並排除 self
        for (SelectionKey key : selector.keys()) {

            //通過 key 獲取到對應的 channel
            Channel targetChannel = key.channel();

            //排除自己
            if (targetChannel instanceof SocketChannel && targetChannel != self) {
                //轉型
                SocketChannel dest = (SocketChannel) targetChannel;
                //將msg儲存到 buffer
                ByteBuffer buffer = ByteBuffer.wrap(msg.getBytes());
                //將 buffer 的資料寫入通道
                dest.write(buffer);
            }
        }
    }


    public static void main(String[] args) {
        //建立伺服器物件
        GroupChatServer groupChatServer = new GroupChatServer();
        groupChatServer.listen();
    }
}

三、客戶端

public class GroupChatClient {

    //定義相關的屬性
    // 伺服器的ip
    private static final String HOST = "127.0.0.1";
    //伺服器埠
    private static final Integer PORT = 6667;
    private Selector selector;
    private SocketChannel socketChannel;
    private String userName;

    //構造器，完成初始化工作
    public GroupChatClient() {
        try {
            //獲取選擇器
            selector = Selector.open();
            System.out.println("selector = " + selector);
            //連線伺服器
            socketChannel = SocketChannel.open(new InetSocketAddress(HOST, PORT));
            //設定非阻塞
            socketChannel.configureBlocking(false);
            //將 socketChannel 註冊到 selector
            socketChannel.register(selector, SelectionKey.OP_READ);
            //得到 userName
            userName = socketChannel.getLocalAddress().toString().substring(1);
            System.out.println(userName + " is ok...");

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //向伺服器傳送訊息
    public void sendInfo(String info) {
        info = userName + "說：" + info;

        try {
            socketChannel.write(ByteBuffer.wrap(info.getBytes()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //讀取從伺服器端回覆的訊息
    public void readInfo() {

        try {
            int readChannels = selector.select();
            //有可以用的通道
            if (readChannels > 0) {
                Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
                while (iterator.hasNext()) {

                    SelectionKey key = iterator.next();
                    if (key.isReadable()) {
                        //得到相關的通道
                        SocketChannel socketChannel = (SocketChannel) key.channel();
                        //得到一個 Buffer
                        ByteBuffer buffer = ByteBuffer.allocate(1024);
                        //讀取
                        socketChannel.read(buffer);
                        //把讀到的緩衝區的資料轉成字串
                        String msg = new String(buffer.array());
                        System.out.println(msg.trim());
                    }
                }

                //刪除當前的selectionKey, 防止重複操作
                iterator.remove();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    public static void main(String[] args) {
        //啟動客戶端
        GroupChatClient chatClient = new GroupChatClient();


        //啟動一個執行緒，每隔3秒，讀取從伺服器傳送的資料
        new Thread() {
            @Override
            public void run() {
                System.out.println("讀取資訊");
                chatClient.readInfo();
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();

        //傳送資料給伺服器
        Scanner scanner = new Scanner(System.in);

        while (scanner.hasNextLine()) {
            String s = scanner.nextLine();
            chatClient.sendInfo(s);
        }
    }
}