Java到FileZilla FTP客户端：套接字写入错误

Question

这些天，另一个挑战使我震惊。 我正在尝试用Java创建FTP服务器，该服务器应该能够与FileZilla FTP客户端进行通信。 代码不是最好的，因为我尝试了很多事情来找出正在发生的事情。

这是FileZilla日志从德语翻译而来

Status: Connect to 127.0.0.1:21...
Status: Connected!Waiting for welcome message.
Response:    220 localhost connected
Error:  Establishing connection to server failed.

到目前为止，主要问题是建立实际连接。 套接字已连接，我可以向客户端发送至少一条消息，但是没有机会获得客户端输入，例如PASV，USER和PASS。

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;

import javax.swing.JButton;
import javax.swing.JFrame;

public class FTP_Server extends JFrame implements ActionListener, WindowListener {
    private static final long serialVersionUID = 1L;

    private Container cp;
    private JButton btncon;
    private ServerSocket listenSocket;
    private Socket connectionSocket;
    private DataOutputStream dos;
    private DataInputStream dis;
    private OutputStream os;
    private InputStream is;

    public FTP_Server() {
        super("FTP Server");

        this.setDefaultCloseOperation(EXIT_ON_CLOSE);

        cp = this.getContentPane();
        cp.setLayout(new BorderLayout());

        btncon = new JButton("Connect");
        btncon.addActionListener(this);

        cp.add(btncon, BorderLayout.CENTER);

        this.pack();
        this.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if(e.getSource().equals(btncon)){
            createConnection();
        }
    }

    public void createConnection() {
        System.out.println("Connecting...");
        try {
            listenSocket = new ServerSocket(21);
            listenSocket.setSoTimeout(0);
            connectionSocket = listenSocket.accept();
            connectionSocket.setSoLinger(true, 0);
            connectionSocket.setSoTimeout(0);
            connectionSocket.setKeepAlive(true);
            System.out.println("Connected!");

            os = connectionSocket.getOutputStream();
            dos = new DataOutputStream(os);

            is = connectionSocket.getInputStream();
            dis = new DataInputStream(is);

            while(connectionSocket.isConnected() == true) {
                dos.writeUTF("220 localhost connected\r\n");
                //Will cause socket write error soon!
                dos.flush();
                dos.writeUTF("331 Anonym no password needed\r\n");
                System.out.println(is.read());
            }
        } catch (SocketException exp) {
            try {
                listenSocket.close();
                System.out.println("Disconnected");
                exp.printStackTrace();
            } catch (IOException exp2) {
                exp2.printStackTrace();
            }
        } catch (IOException exp) {
            exp.printStackTrace();
        }
    }

    @Override
    public void windowOpened(WindowEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void windowClosing(WindowEvent e) {
        System.exit(0);
    }

    @Override
    public void windowClosed(WindowEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void windowIconified(WindowEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void windowDeiconified(WindowEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void windowActivated(WindowEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void windowDeactivated(WindowEvent e) {
        // TODO Auto-generated method stub

    }
}

对于错误消息/打印堆栈：

java.net.SocketException: Software caused connection abort: socket write error
    at java.net.SocketOutputStream.socketWrite0(Native Method)
    at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:109)
    at java.net.SocketOutputStream.write(SocketOutputStream.java:153)
    at java.io.DataOutputStream.write(DataOutputStream.java:107)
    at java.io.DataOutputStream.writeUTF(DataOutputStream.java:401)
    at java.io.DataOutputStream.writeUTF(DataOutputStream.java:323)
    at ftp.FTP_Server.createConnection(FTP_Server.java:82)
    at ftp.FTP_Server.actionPerformed(FTP_Server.java:58)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6505)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.java:2273)
    at java.awt.Window.dispatchEventImpl(Window.java:2719)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:682)
    at java.awt.EventQueue$3.run(EventQueue.java:680)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:696)
    at java.awt.EventQueue$4.run(EventQueue.java:694)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

Answer 1

这里有很多错误。

1. 不要搞混SO_LINGER。 这是没有必要的，只会造成进一步的不必要的痛苦。
2. writeUTF（）写入仅readUTF（）可以读取的格式。 这不是与非Java客户端通信的方法。
3. 您无需在单独的线程中处理已接受的套接字，因此一次只能处理一个客户端。
4. isConnected（）不是对连接状态的有效测试。 它告诉您是否连接了插座。 您这样做了，所以它将返回true。 当对等方断开连接时，这不会改变。 您需要使用各种读取的API中记录的常规方法测试EOS。
5. 当您在接受的套接字上获得IOException时，无需关闭侦听套接字。
6. 我不明白为什么FTP服务器需要GUI，但如果这样做，它必须在与AWT线程不同的线程上执行所有网络I / O，包括接受连接。
7. 您只需要告诉客户端他已经成功连接了一次，而不是无限次。

这足以进行下去。

Answer 2

我仍然无法处理消息传递。 我现在要做的是为每个连接的套接字以及现在的每个输出流创建一个新线程。

package ftp;

import java.io.DataOutputStream;
import java.io.IOException;

public class MultiIO implements Runnable{
    private DataOutputStream dos;

    public MultiIO(DataOutputStream stream) {
        dos = stream;
        System.out.println("Set OutputStream.");
    }

    @Override
    public void run() {
        try {
            dos.writeBytes("220");
            dos.flush();
            System.out.println("tried once");
        } catch (IOException e) {
            System.exit(-1);
        }
    }
}

现在的麻烦是FileZilla客户端不会收到220消息。

这是新的套接字处理类。 我有点从oracle页面复制了它。

package ftp;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;
import java.net.SocketException;

public class MultiConnection implements Runnable{
    private Socket cSocket;

    public MultiConnection(Socket client) {
        cSocket = client;
        System.out.println("Connected!");
    }

    @Override
    public void run() {
        OutputStream os = null;
        DataOutputStream dos = null;
        try {
            os = cSocket.getOutputStream();
            dos = new DataOutputStream(os);
        } catch (SocketException es) {
            es.printStackTrace();
        } catch (IOException e) {
            System.exit(-1);
        }

        MultiIO mio;
        mio = new MultiIO(dos);
        Thread thio = new Thread(mio);
        thio.start();
    }
}