java - Java 到 FileZilla FTP 客户端：套接字写入错误

Question

这些天，另一个挑战让我头疼。我正在尝试用 Java 创建一个应该能够与 FileZilla FTP 客户端通信的 FTP 服务器。该代码不是最好的，因为我尝试了很多东西来找出发生了什么。

这里是从德语翻译的 FileZilla 日志

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

到目前为止的主要问题是建立真正的连接。套接字已连接，我可以将至少一条消息发送回客户端，但没有机会获取客户端输入，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)

score 0 · Accepted Answer

这里有很多错误。

不要乱用 SO_LINGER。这不是必需的，它只会导致更多不必要的痛苦。
writeUTF() 写入只有 readUTF() 可以读取的格式。这不是一种与非 Java 客户端进行通信的方式。
您不是在单独的线程中处理接受的套接字，因此您一次只能处理一个客户端。
isConnected() 不是对连接状态的有效测试。它会告诉您是否曾经连接过套接字。你做到了，所以它会返回true。当对等方断开连接时，这不会改变。您需要以通常的方式测试 EOS，并记录在各种读取 API 中。
当您在接受的套接字上获得 IOException 时，您不需要关闭侦听套接字。
我不明白为什么 FTP 服务器需要 GUI，但如果需要，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。
你只需要告诉客户端他已经连接成功一次，而不是无限次。

这已经足够了。

score 0 · Accepted Answer

我仍然遇到消息传递问题。我现在所做的是为每个连接的套接字以及每个现在的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);
        }
    }
}

现在的问题是 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();
    }
}

java - Java 到 FileZilla FTP 客户端：套接字写入错误

2 回答 2

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