NIO TimeClient

public class NIOTimeClient {
    //本地默认端口号
    private static final int LOCAL_PORT = 3738;
    //服务端默认端口号
    private static final int REMOTE_PORT = 8585;
    public static void main(String[] args) {
        new Thread(new TimeClientHandler("127.0.0.1", REMOTE_PORT)).start();
    }
    private static class TimeClientHandler implements Runnable {
        private String host;
        private int port;
        private Selector selector;
        private SocketChannel socketChannel;
        private volatile boolean stop = false;
        public TimeClientHandler(String host, int port) {
            this.host = host;
            this.port = port;
            try {
                selector = Selector.open();
                socketChannel = SocketChannel.open();
                //从本地3738端口连接
                socketChannel.bind(new InetSocketAddress(LOCAL_PORT));
                socketChannel.configureBlocking(false);
                System.out.println("TimeClient started at port " + LOCAL_PORT);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        @Override
        public void run() {
            try {
                doConnect();
            } catch (IOException e) {
                e.printStackTrace();
                System.exit(1);
            }
            while (!stop) {
                try {
                    //选择就绪通道
                    selector.select(1000);
                    Set<SelectionKey> selectionKeys = selector.selectedKeys();
                    Iterator<SelectionKey> it = selectionKeys.iterator();
                    SelectionKey selectionKey;
                    while (it.hasNext()) {
                        selectionKey = it.next();
                        it.remove();
                        try {
                            handleInput(selectionKey);
                        } catch (Exception e) {
                            if (null != selectionKey) {
                                selectionKey.cancel();
                                if (null != selectionKey.channel()) {
                                    selectionKey.channel().close();
                                }
                            }
                        }
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            //停止 关闭selector
            if(null != selector){
                try {
                    System.out.println("关闭selector");
                    //selector关闭之后 注册在其上面的channel都会关闭
                    selector.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        /**
         * 处理输入
         */
        private void handleInput(SelectionKey selectionKey) throws IOException {
            if(selectionKey.isValid()){
                //获取key对应的channel
                SocketChannel channel = (SocketChannel) selectionKey.channel();
                //首先判断connection
                if(selectionKey.isConnectable()){
                    if(channel.finishConnect()){
                        channel.register(selector,SelectionKey.OP_READ);
                        doWrite(channel);
                    }else {
                        System.exit(1);
                    }
                }
                //判断是否可读
                if(selectionKey.isReadable()){
                    ByteBuffer buffer = ByteBuffer.allocate(1025-1);
                    int read = channel.read(buffer);
                    if(read>0){
                        //回绕缓冲区 方便读取
                        buffer.flip();
                        byte[] elements = new byte[buffer.remaining()];
                        buffer.get(elements);
                        String content = new String(elements,StandardCharsets.UTF_8);
                        System.out.println("The time client received time : " + content);
                        stop = true;
                    }else if(read < 0){
                        selectionKey.cancel();
                        channel.close();
                    }else {
                        //读到0字节 忽略
                    }
                }
            }
        }
        private void doConnect() throws IOException {
            //如果直接连接成功 就将其注册到selector并监听读取就绪事件
            if (socketChannel.connect(new InetSocketAddress(host, port))) {
                socketChannel.register(selector, SelectionKey.OP_READ);
                doWrite(socketChannel);
            } else {
                //没有连接成功 就注册 注意这里是OP_CONNECT
                socketChannel.register(selector, SelectionKey.OP_CONNECT);
            }
        }
        private void doWrite(SocketChannel socketChannel) throws IOException {
            byte[] request = "QUERY TIME ORDER ".getBytes(StandardCharsets.UTF_8);
            ByteBuffer byteBuffer = ByteBuffer.allocate(request.length);
            byteBuffer.put(request);
            byteBuffer.flip();
            socketChannel.write(byteBuffer);
            if (!byteBuffer.hasRemaining()) {
                System.out.println("Send order to server successfully.");
            }
        }
    }
}