Netty: NIO Selector选择器（C/S demo详细注释与源码）

public static void main(String[] args) throws Exception {  
//创建服务端通道，用 open 获取
        ServerSocketChannel ServerChannel = ServerSocketChannel.open();
        //设置 ip 和端口号
        SocketAddress address = new InetSocketAddress("127.0.0.1", 4321);
        //绑定到 服务通道 的 socket
        ServerChannel.socket().bind(address);

        //等待客户端连接
        SocketChannel socketChannel = ServerChannel.accept();

        //    处理数据 通过 buffer 来
        ByteBuffer writebuffer = ByteBuffer.allocate(128);
        writebuffer.put("hello client i am server".getBytes());
        writebuffer.flip();
        socketChannel.write(writebuffer);

        //    读取客户端的数据
        ByteBuffer readbuffer = ByteBuffer.allocate(128);
        StringBuffer stringBuffer = new StringBuffer();
        socketChannel.read(readbuffer);
        readbuffer.flip();
        while (readbuffer.hasRemaining()) {
            stringBuffer.append((char) readbuffer.get());
        }
        System.out.println("client data :" + stringBuffer.toString());

        socketChannel.close();
        ServerChannel.close();
}

  public static void main(String[] args) throws Exception {
        //开启一个 socket 通道
        SocketChannel socketChannel = SocketChannel.open();
        //设置 ip 和端口号
        SocketAddress address = new InetSocketAddress("127.0.0.1", 4321);
        //连接 这个 address
        socketChannel.connect(address);

        //    先写后读
        //    处理数据 通过 buffer 来
        ByteBuffer writebuffer = ByteBuffer.allocate(128);
        writebuffer.put("hello server i am client ".getBytes());
        writebuffer.flip();
        socketChannel.write(writebuffer);

        //    读取客户端的数据
        ByteBuffer readbuffer = ByteBuffer.allocate(128);
        StringBuffer stringBuffer = new StringBuffer();
        socketChannel.read(readbuffer);
        readbuffer.flip();
        while (readbuffer.hasRemaining()) {
            stringBuffer.append((char) readbuffer.get());
        }
        System.out.println("server data :" + stringBuffer.toString());
        socketChannel.close();
    }

public static void main(String[] args) throws Exception {
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        //设置 ip 和端口号
        SocketAddress address = new InetSocketAddress("127.0.0.1", 4321);
        //绑定到 服务通道 的 socket
        serverSocketChannel.socket().bind(address);

        //     将这个 channel 设置成非阻塞的
        serverSocketChannel.configureBlocking(false);
        //    打开一个选择器
        Selector selector = Selector.open();
        //    将通道注册到选择其中  声明选择器监听事件
        //    通常来说，我们监听的是 连接事件
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        /*
         * 通过选择器来管理通道
         * 需要感知， 被监听的通道 有没有事件触发
         * 当 select 方法 返回值 >0 的时候就代表 当前有多少个操作要处理
         * 所以我们需要一直轮询 它是否有时间要处理
         * */
        while (true) {
            int ready = selector.select();
            if (ready == 0) {
                continue;
            }
            //    通过 Selected keys 获取到操作集合
            Set<SelectionKey> set = selector.selectedKeys();
            Iterator<SelectionKey> iterator = set.iterator();
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                //    为了 避免重复操作 我们处理一个就移出一个
                iterator.remove();
                //我们通过 key 中的方法 来判断要处理什么操作
                /*
                 * isAcceptable() : 连接
                 * isConnectable() : 就绪
                 * isReadable() : 读取
                 * isWritable() : 写入
                 * */
                if (key.isAcceptable()) {
                    //处理 accpt 事件
                    //获得客户端连接 并且注册 写事件
                    SocketChannel socketChannel = serverSocketChannel.accept();
                    socketChannel.configureBlocking(false);
                    //   处理完 连接状态之后 后续将写操作加入到选择其中
                    socketChannel.register(selector, SelectionKey.OP_WRITE);
                } else if (key.isWritable()) {
                    //    我们处理完连接之后，可以用key来获得对应的事件通道
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    //处理 write 事件
                    ByteBuffer writebuffer = ByteBuffer.allocate(128);
                    writebuffer.put("hello client i am server from 4321".getBytes());
                    writebuffer.flip();
                    socketChannel.write(writebuffer);
                    //我们可以通过 key 来注册接下来发生在这个通道的事件
                    key.interestOps(SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    //处理 read 事件
                    SocketChannel socketChannel = (SocketChannel) key.channel();

                    //    读取客户端的数据
                    ByteBuffer readbuffer = ByteBuffer.allocate(128);
                    //读取数据
                    int read = socketChannel.read(readbuffer);
                    //read = -1 代表着已经读完了
                    if (read == -1) {
                        key.cancel();
                    }
                    //刷新 buffer
                    readbuffer.flip();
                    //用string buffer 来拼接读取的数据
                    StringBuffer stringBuffer = new StringBuffer();
                    while (readbuffer.hasRemaining()) {
                        stringBuffer.append((char) readbuffer.get());
                    }
                    System.out.println("client data :" + stringBuffer.toString());


                } else if (key.isConnectable()) {

                }
            }

        }

    }