用nio写ftpclient（未完）

MyFTP.java

package org.example;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.function.Function;
import java.util.logging.Logger;

public class MyFTP {

    private static Selector selector;
    private static ScheduledExecutorService scheduledExecutor;
    private String hostname;
    //private int port;

    protected int _replyCode;
    protected ArrayList<String> _replyLines;
    protected boolean _newReplyString;
    protected String _replyString;
    protected String _controlEncoding;

    static {
        try {
            selector = Selector.open();
        } catch (IOException e) {
            Logger.getLogger(MyFTP.class.getName()).warning("failed to open selector");
        }
        //TODO set Thread Factory
        scheduledExecutor = Executors.newSingleThreadScheduledExecutor();
        //scheduledExecutor.schedule();
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("connecting...");
        MyFTP myFTP = new MyFTP();
        myFTP.connect("localhost", 21);
    }

    public void connect(String hostname, int port)
            throws SocketException, IOException, InterruptedException {
        this.hostname = hostname;

        //_connect(InetAddress.getByName(hostname), port, null, -1);
        SocketChannel ch = SocketChannel.open();
        ch.configureBlocking(false);
        SelectionKey sk = ch.register(selector, SelectionKey.OP_CONNECT|SelectionKey.OP_READ);
        sk.attach((Function<Void, Void>) nil -> {
            try {
                System.out.println("isConnectable" + sk.isConnectable());
                if (sk.isConnectable()) {
                    SocketChannel socketChannel = (SocketChannel) sk.channel();
                    //System.out.println("connected");
                    socketChannel.finishConnect();
                    doSelect();
                } else if (sk.isReadable()) {
                    System.out.println("isReadable:" + sk.isReadable());
                    ByteBuffer byteBuffer = ByteBuffer.allocate(256);
                    try {
                        SocketChannel ch2 = (SocketChannel) sk.channel();
                        int bytesWrite = ch.read(byteBuffer);
                        if (bytesWrite != -1) {
                            MyFTP.this._replyString = new String(byteBuffer.array(), 0, bytesWrite);
                            System.out.println(MyFTP.this._replyString);
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }


                //socketChannel.finishConnect();


                //ByteBuffer loginBuf = ByteBuffer.wrap("USER user".getBytes());
                //socketChannel.write(loginBuf);
                doSelect();

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

            return null;
        });

        ch.connect(new InetSocketAddress(hostname, port));
        doSelect();
        Thread.sleep(10*1000L);
    }


    private void doSelect() throws IOException {
        selector.select();
        Set<SelectionKey> sks = selector.selectedKeys();
        Iterator<SelectionKey> itr = sks.iterator();
        if (itr.hasNext()) {
            SelectionKey key = itr.next();

                Function<Void,?> fun = (Function<Void, ?>) key.attachment();
                fun.apply(null);

            itr.remove();
        }
    }
}

很多问题没有搞懂
1.模仿org.apache.commons.net.ftp.FTPClient暴露出来的api应该是阻塞式的，MyFTP应该如何去处理从异步到阻塞呢
2.nio的channel如何确定已经读完了返回了呢，需要阅读ftp协议解析control流和data流吗，end_of_file是一个。
3.如何处理与链接池的关系呢
给MyFTP打上标记，是空闲还是使用中来确定是否新建MyFTP实例，而Selector是所有MyFTP公用的，多路复用与多线程编程是不是有冲突呢
我觉得应该多点从Netty实现中获得参考。