使用NIO实现多人聊天

前言

基于NIO实现多人模拟聊天窗口，首先要了解，NIO组件，ServerSocketChannel、SocketChannel、Selector、SelectorKey。了解了他们各自作用以及关系，多人聊天系统很容易理解实现，这里不在介绍，自行了解

服务器端

1. 初始化服务端ServeSocketChannel 连接，绑定端口，并注册到Selector
2. 通过Selectors 监听注册通道事件，根据事件进行用户上线、下线、消息读取、转发处理

public class ChatServer {

    private ServerSocketChannel serverSocketChannel;
    private static final int PORT = 9527;
    private Selector selector;

    /**
     * 初始化
     *
     * @throws Exception
     */
    public void initServer() throws Exception {
        selector = Selector.open();
        serverSocketChannel.socket().bind(new InetSocketAddress(PORT));
        serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.register(selector, SelectionKey.OP_READ);
        serverSocketChannel.configureBlocking(false);

    }

    /**
     * 接受/转发客户端消息
     */
    public void receiveClientInfo() throws Exception {

        while (true) {
            int select = selector.select();
            if (select > 0) {
                Set<SelectionKey> selectionKeys = selector.selectedKeys();
                Iterator<SelectionKey> iterators = selectionKeys.iterator();

                while (iterators.hasNext()) {
                    //获取监听 key对象
                    SelectionKey key = iterators.next();
                    //有客户端连接
                    if (key.isAcceptable()) {
                        //获取socketChannel 客户端连接
                        SocketChannel socketChannel = serverSocketChannel.accept();
                        //设置非阻塞
                        socketChannel.configureBlocking(false);
                        //socketChannel 注册到selector 上
                        socketChannel.register(selector, SelectionKey.OP_ACCEPT);
                        //用户上线提醒
                        System.out.println("有用户上线：" + socketChannel.getRemoteAddress());
                    }

                    SocketChannel socketChannel = null;
                    try {
                        //读操作
                        if (key.isReadable()) {
                           socketChannel = (SocketChannel) key.channel();
                            //将数据从通道读取到缓冲区
                            ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
                            int read = socketChannel.read(byteBuffer);
                            if (read > 0) {
                                String msg = new String(byteBuffer.array());
                                System.out.println("读取到数据:" + msg);
                                //转发消息给其它用户
                                tranceMessage2OtherClient(msg, socketChannel);
                            }
                        }
                    }catch (IOException e){
                        System.out.println("用户下线:"+socketChannel.getRemoteAddress());
                        key.cancel();
                        socketChannel.close();
                    }
                    //删除处理过的key
                    iterators.remove();
                }
            }
        }
    }

    /**
     * 转发消息到其他客户端
     *
     * @param msg
     * @param selfChannel
     */
    private void tranceMessage2OtherClient(String msg, SocketChannel selfChannel) throws Exception {

        Set<SelectionKey> keys = selector.keys();
        for (SelectionKey key : keys) {
            Channel channel = key.channel();
            //发送者不接受消息
            if (channel instanceof SocketChannel && !channel.equals(selfChannel)) {
                SocketChannel targetChannel = (SocketChannel) channel;
                //消息写入到目标通道
                int write = targetChannel.write(ByteBuffer.wrap(msg.getBytes()));
            }
        }
    }
}

客户端

1. 客户端初始化，并注册到selecotrs 上
2. 发送消息到服务器
3. 通过Selectors 监听通道读事件，读取消息

public class ChatClient {

    private SocketChannel socketChannel;
    private String host = "127.0.0.1";
    private static final int PORT = 9527;
    private Selector selector;
    private String localFlag;

    /**
     * 初始客户端连接
     *
     * @throws Exception
     */
    public void initClient() throws Exception {
        socketChannel = SocketChannel.open(new InetSocketAddress(host, PORT));
        socketChannel.configureBlocking(false);
        selector = Selector.open();
        socketChannel.register(selector, SelectionKey.OP_READ);
        localFlag = socketChannel.getLocalAddress().toString().substring(1);
        System.out.println("客户端初始化完成..." + localFlag);
    }

    /**
     * 发送消息
     *
     * @param msg
     */
    public void sendMsg(String msg) {
        msg += localFlag + "->" + msg;

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

    /**
     * 接受消息
     */
    public void receiveMsg() {

        try {
            int channels = selector.select();

            if (channels > 0) {
                Set<SelectionKey> selectionKeys = selector.selectedKeys();
                Iterator<SelectionKey> iterator = selectionKeys.iterator();
                while (iterator.hasNext()) {
                    SelectionKey selectionKey = iterator.next();
                    if (selectionKey.isReadable()) {
                        SocketChannel channel = (SocketChannel) selectionKey.channel();
                        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
                        channel.read(byteBuffer);
                        String readMsg = new String(byteBuffer.array());
                        System.out.println("读取消息:" + readMsg);
                    }
                }
                iterator.remove();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

总结

NIO 多人聊天实现，主要依靠NIO Seletors 实现，Selectors 接受服务于客户端注册，并监听每个通道的事件，一旦有事件发生，即可进行处理。注册的事件即(Channel) 都会生成相应SelectKey, 通过 SelectKey可以发现获取，有事件发生的通道。